[solr] branch main updated: SOLR-15898 Upgrade-notes and major-changes for 9.0 (#769)

[ja...@apache.org]

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The following commit(s) were added to refs/heads/main by this push:
     new 989f22c0355 SOLR-15898 Upgrade-notes and major-changes for 9.0 (#769)
989f22c0355 is described below

commit 989f22c03551e18c36c45d949b585b755ab10798
Author: Jan Høydahl <ja...@users.noreply.github.com>
AuthorDate: Sun Apr 10 00:42:54 2022 +0200

    SOLR-15898 Upgrade-notes and major-changes for 9.0 (#769)
    
    * Add "Major changes in earlier 8.x versions" to major-changes-in-solr-9.adoc
    * Start re-organizing major-changes-in-solr-9.adoc with sub headings
    * Edited the Upgrade Prerequisites section, Added "master/slave" warning
    * Edited the "Rolling Upgrades" section.
---
 .../authentication-and-authorization-plugins.adoc  |   1 +
 .../pages/major-changes-in-solr-9.adoc             | 924 ++++++++++++++++++++-
 .../upgrade-notes/pages/solr-upgrade-notes.adoc    | 829 +-----------------
 3 files changed, 898 insertions(+), 856 deletions(-)

diff --git a/solr/solr-ref-guide/modules/deployment-guide/pages/authentication-and-authorization-plugins.adoc b/solr/solr-ref-guide/modules/deployment-guide/pages/authentication-and-authorization-plugins.adoc
index c0940e39bbf..2d2d75bb2af 100644
--- a/solr/solr-ref-guide/modules/deployment-guide/pages/authentication-and-authorization-plugins.adoc
+++ b/solr/solr-ref-guide/modules/deployment-guide/pages/authentication-and-authorization-plugins.adoc
@@ -207,6 +207,7 @@ Solr has a built-in `PKIAuthenticationPlugin` (described below) that is always a
 Each Authentication plugin may also decide to secure inter-node requests on its own.
 They may do this through the so-called `HttpClientBuilder` mechanism, or they may alternatively choose on a per-request basis whether to delegate to PKI or not by overriding a `interceptInternodeRequest()` method from the base class, where any HTTP headers can be set.
 
+[#pkiauthenticationplugin]
 === PKIAuthenticationPlugin
 
 The `PKIAuthenticationPlugin` provides a built-in authentication mechanism where each Solr node is a super user and is fully trusted by other Solr nodes through the use of Public Key Infrastructure (PKI).
diff --git a/solr/solr-ref-guide/modules/upgrade-notes/pages/major-changes-in-solr-9.adoc b/solr/solr-ref-guide/modules/upgrade-notes/pages/major-changes-in-solr-9.adoc
index 22181ca9543..69a955aa231 100644
--- a/solr/solr-ref-guide/modules/upgrade-notes/pages/major-changes-in-solr-9.adoc
+++ b/solr/solr-ref-guide/modules/upgrade-notes/pages/major-changes-in-solr-9.adoc
@@ -26,71 +26,51 @@ Before starting an upgrade to Solr 9, please take the time to review all informa
 
 You should also consider all changes that have been made to Solr in any version you have not upgraded to already. For example, if you are currently using Solr 8.1, you should review changes made in all subsequent 8.x releases in addition to changes for 9.0.
 
-A thorough review of the list in Major Changes in Earlier 8.x Versions as well as the {solr-javadocs}/changes//Changes.html[CHANGES.txt] in your Solr instance will help you plan your migration to Solr 9.
+A thorough review of the list in xref:major-changes-in-earlier-8-x-versions[Major Changes in Earlier 8.x Versions] as well as the {solr-javadocs}/changes/Changes.html[CHANGES.txt] in your Solr instance will help you plan your migration to Solr 9.
 
 === Upgrade Prerequisites
 
-* LUCENE-8738: Move to Java 11 as minimum Java version.
+*Solr 9 requires Java 11 as minimum Java version, and is also tested with Java 17.*
 
-* Upgrade all collections in `stateFormat=1` to `stateFormat=2` *before* upgrading to Solr 9, as Solr 9 does not support the older format and no longer supports migrating collections from the older format to the current format (previously known as stateFormat=2).
-Upgrade is to be done using Collection API MIGRATESTATEFORMAT action using a previous version of Solr.
-See for example https://solr.apache.org/guide/8_8/cluster-node-management.html#migratestateforma[Solr 8.8 Ref Guide].
-// Can't link directly to .adoc file, need to link to 8.something ref guide as MIGRATESTATEFORMAT no longer exists in 9.0.
+If using Solr's Java client (*SolrJ*) with `CloudSolrClient` to connect to your SolrCloud cluster, make sure to upgrade SolrJ in all your client applications to version 8.10 or higher (8.x), before upgrading your SolrCloud cluster to version 9.0. Otherwise, SolrJ will not be able to connect to the cluster once it has upgraded to Solr 9. Once you have upgraded all Solr clusters that the client is connecting to, you can upgrade the SolrJ client to 9.x.
 
-* SOLR-12823: Remove `/clusterstate.json` support, i.e., support for collections created with `stateFormat=1` as well as support for Collection API MIGRATESTATEFORMAT action.
-Also removes support for cluster property `legacyCloud` (as if always false now).
+If you have an old collection that was initially created with a Solr version prior to 5.0, that collection Solr may keep that collection's state in the `/clusterstate.json` file at the root of Zookeeper. Solr 9 does no longer support this file. You must upgrade such collections to the new per-collection `state.json` format *before* upgrading to Solr 9. This is done by calling the https://solr.apache.org/guide/8_11/cluster-node-management.html#migratestateformat[Collection API MIGRATESTAT [...]
 
-* If you're using a SolrJ CloudClient to connect to your Solr cluster, you must be using SolrJ version 8.10 or higher (8.x) when upgrading your SolrCloud from 8.x to 9.x.
-Otherwise, SolrJ will not be able to connect to the cluster once it has upgraded to Solr 9.
-Once you have upgraded all Solr clusters that the client is connecting to, you can upgrade the SolrJ client to 9.x.
+If you are using Solr in standalone mode with the xref:query-guide:query-elevation-component.adoc[] with it's elevation file in the data directory, you'll have to move it to the xref:configuration-guide:config-sets.adoc[Configset] folder instead.
 
-* If you're using Solr in standalone mode with the xref:query-guide:query-elevation-component.adoc[] with it's elevation file in the data directory, you'll have to move it to the xref:configuration-guide:config-sets.adoc[Configset] instead.
-The only reason QEC supported the data directory was to support loading its changes on a commit instead of a more expensive core reload.
-That feature now works from the configset dir too.
-SolrCloud doesn't support that but may sometime.
+Some metrics have changed names due to the removal of "master" and "slave" terminology in 8.x. If you rely on metrics, alerts and monitors on Solr KPIs that mention "master" or "slave", you will need to prepare for those metrics now appearing with "leader" and "follower" in their names instead.
 
 === Rolling Upgrades
 
-WARNING: Rolling upgrades from Solr 8 to Solr 9 require upgrading from Solr 8.7 or newer.
+If you are planning to upgrade your cluster using a rolling upgrade model (upgrade each node in succession, as opposed to standing up a brand new 9.x cluster), please read the following carefully.
+
+Rolling upgrades from Solr 8 to Solr 9 require upgrading from Solr 8.7 or newer. If you run an 8.x. version prior to 8.7 we recommend that you first upgrade to 8.11.
+
+*PKI Authentication*
+
+Internode communication secured by PKI Authentication has changed formats. For detailed information, see
+xref:deployment-guide:authentication-and-authorization-plugins.adoc#pkiauthenticationplugin[PKI Authentication Plugin].
 
-* SOLR-14702: All references to "master" and "slave" were replaced in the code with "leader" and "follower".
-This includes API calls for the replication handler and metrics.
-Some metrics also changed, alerts and monitors on Solr KPIs that mention "master" or "slave" will also now be "leader" and "follower"
+A rolling upgrade from Solr 8 to Solr 9 requires the following multiple restart sequence:
 
-* SOLR-15965: Internode communication secured by PKI Authentication has changed formats. For detailed information, see
-  xref:deployment-guide:authentication-and-authorization-plugins.adoc#pkiauthenticationplugin[PKI Authentication Plugin].
-  A rolling upgrade from Solr 8 to Solr 9 requires the following multiple restart sequence:
 1. Upgrade to Solr 9 and set system properties: `solr.pki.sendVersion=v1` and `solr.pki.acceptVersions=v1,v2`. This will allow Solr 9 nodes to send messages to Solr 8 nodes while the upgrade is in progress.
 2. Restart with `solr.pki.sendVersion=v2` (default, can be unset) and `solr.pki.acceptVersions=v1,v2`. This will force all nodes to send the new header.
 3. (Optional) Restart with system property `solr.pki.acceptVersions=v2` (default, can be unset) to prevent outdated nodes from connecting to your cluster.
 
 === Reindexing After Upgrade
 
-In Solr 8, it's possible to add docValues to a schema without re-indexing via `UninvertDocValuesMergePolicy`, an advanced/expert utility.
-Due to changes in Lucene 9, that isn't possible any more; the component was removed.
-If re-indexing is too onerous, use this mechanism in Solr 8.
-
-=== Solr Binary Release `dist/` Directory
-
-The `dist/` directory in the Solr binary release has been removed as of Solr 9.0.
+It is always strongly recommended that you fully reindex your documents after a major version upgrade. For details, see the xref:indexing-guide:reindexing.adoc[] section, which covers several strategies for how to reindex.
 
-* The `solr-core` and `solr-solrj` jars can be found under `server/solr-webapp/webapp/WEB-INF/lib/`.
-* The Solr module jars can be found in `modules/<module-name>/lib`, packaged individually for each module.
-* The `solrj-deps` (SolrJ Dependencies) are no longer separated out from the other Server jars.
-Please refer to the SolrJ Maven artifact to see the exact dependencies you need to include from `server/solr-webapp/webapp/WEB-INF/lib/` and `server/lib/ext/` if you are loading in SolrJ manually.
-If you plan on using SolrJ as a JDBC driver, please refer to the xref:query-guide:sql-query.adoc#generic-clients[JDBC documentation]
+In Solr 8, it's possible to add docValues to a schema without re-indexing via `UninvertDocValuesMergePolicy`, an advanced/expert utility.
+Due to changes in Lucene 9, that isn't possible anymore; the component was removed.
 
-== Solr 9.0 Raw Notes
+== Solr 9.0 Raw Notes (NOT YET EDITED)
 
 _(raw; not yet edited)_
 
 
-* SOLR-13671: Allow 'var' keyword in Java sources
 
-* SOLR-12055 introduces async logging by default. There's a small window where log messages may be lost in the event of some hard crash.
-Switch back to synchronous logging if this is unacceptable, see comments in the log4j2 configuration files (log4j2.xml by default).
 
-* SOLR-13323: The unused package org.apache.solr.internal.csv.writer and associated classes/tests that were easily confused with but not used by org.apache.solr.response.CSVWriter (or any other code) have been removed
 
 * SOLR-13854, SOLR-13858: SolrMetricProducer / SolrInfoBean APIs have changed and third-party components that implement these APIs need to be updated.
 
@@ -146,6 +126,32 @@ named "internal".  The sample Grafana dashboard now filters to include or exclud
 
 == New Features & Enhancements
 
+// Fill these sub headings
+
+=== Docker
+
+=== Security
+
+=== Scalability
+
+=== Modules
+
+* HDFS
+* Hadoop-auth
+* GCS-repository
+* JWT-auth
+* Scripting
+* SQL
+
+
+=== Gradle build
+
+=== Other
+
+* SOLR-13671: Allow 'var' keyword in Java sources
+
+// TBD
+
 * Replica placement plugins
 
 * Rate limiting and task management
@@ -156,6 +162,22 @@ named "internal".  The sample Grafana dashboard now filters to include or exclud
 
 == Configuration and Default Parameter Changes
 
+// TODO: Move into sub headings
+
+=== Schema Changes in 9.0
+
+=== Indexing Changes in 9.0
+
+=== Query Changes in 9.0
+
+=== Authentication & Security Changes in 9.0
+
+=== UI Changes in 9.0
+
+=== Dependency Updates in 9.0
+
+// RAW notes below
+
 * SOLR-7530: TermsComponent's JSON response format was changed so that "terms" property carries per field arrays by default regardless of distrib, terms.list, terms.ttf parameters.
 This affects JSON based response format but not others
 
@@ -203,6 +225,9 @@ values serialized in this way will need to be updated accordingly.
 * SOLR-12901: Highlighting: hl.method=unified is the new default.  Use hl.method=original
   to switch back if needed.
 
+* SOLR-12055 introduces async logging by default. There's a small window where log messages may be lost in the event of some hard crash.
+Switch back to synchronous logging if this is unacceptable, see comments in the log4j2 configuration files (log4j2.xml by default).
+
 === solr.xml maxBooleanClauses now enforced recursively
 
 Lucene 9.0 has additional safety checks over previous versions that impact how the `solr.xml` global xref:configuration-guide:configuring-solr-xml#global-maxbooleanclauses[`maxBooleanClauses`] option is enforced.
@@ -306,6 +331,9 @@ This includes:
 * SOLR-14783: Data Import Handler (DIH) has been removed from Solr.
 The community package is available at: https://github.com/rohitbemax/dataimporthandler
 
+* SOLR-12823: Remove `/clusterstate.json` support, i.e., support for collections created with `stateFormat=1` as well as support for Collection API MIGRATESTATEFORMAT action.
+Also removes support for cluster property `legacyCloud` (as if always false now).
+
 * SOLR-14792: VelocityResponseWriter has been removed from Solr.
 This encompasses all previous included `/browse` and `wt=velocity` examples.
 This feature has been migrated to an installable package at https://github.com/erikhatcher/solr-velocity
@@ -347,4 +375,820 @@ where they really belong: /admin/threads, /admin/properties, /admin/logging
 
 * Atomic/partial updates to nested documents now _require_ the `\_root_` field to clearly show the document isn't a root document.  Solr 8 would fallback on the `\_route_` param but no longer.
 
-* SolrJ: The project is migrating away from the Apache HttpClient dependency in favor of Jetty's client (supporting HTTP/2), to occur over the 9x releases.  We deprecated HttpSolrClient and friends in favor of Http2SolrClient and equivalents.  For SolrCloud, the former CloudSolrClient was renamed CloudLegacySolrClient (deprecated), and instead BaseCloudSolrClient was renamed to CloudSolrClient and given a Builder for the Jetty based HTTP/2 client.
\ No newline at end of file
+* SolrJ: The project is migrating away from the Apache HttpClient dependency in favor of Jetty's client (supporting HTTP/2), to occur over the 9x releases.  We deprecated HttpSolrClient and friends in favor of Http2SolrClient and equivalents.  For SolrCloud, the former CloudSolrClient was renamed CloudLegacySolrClient (deprecated), and instead BaseCloudSolrClient was renamed to CloudSolrClient and given a Builder for the Jetty based HTTP/2 client.
+
+* SOLR-13323: The unused package org.apache.solr.internal.csv.writer and associated classes/tests that were easily confused with but not used by org.apache.solr.response.CSVWriter (or any other code) have been removed
+
+=== Solr Binary Release `dist/` Directory
+
+The `dist/` directory in the Solr binary release has been removed as of Solr 9.0.
+
+* The `solr-core` and `solr-solrj` jars can be found under `server/solr-webapp/webapp/WEB-INF/lib/`.
+* The Solr module jars can be found in `modules/<module-name>/lib`, packaged individually for each module.
+* The `solrj-deps` (SolrJ Dependencies) are no longer separated out from the other Server jars.
+Please refer to the SolrJ Maven artifact to see the exact dependencies you need to include from `server/solr-webapp/webapp/WEB-INF/lib/` and `server/lib/ext/` if you are loading in SolrJ manually.
+If you plan on using SolrJ as a JDBC driver, please refer to the xref:query-guide:sql-query.adoc#generic-clients[JDBC documentation]
+
+[#major-changes-in-earlier-8-x-versions]
+== Major Changes in Earlier 8.x Versions
+
+The following is a list of major changes released between Solr 8.1 and 8.11.
+
+Please be sure to review this list so you understand what may have changed between the version of Solr you are currently running and Solr 9.0.
+
+=== Solr 8.11
+
+See the https://cwiki.apache.org/confluence/display/SOLR/Release+Notes+8.11[8.11 Release Notes^]
+for an overview of the main new features of Solr 8.11.
+
+When upgrading to 8.11.x users should be aware of the following major changes from 8.10.
+
+*Support for Multiple Authentication Schemes*
+
+Two new authentication and authorization plugins provide support for configuring multiple authentication schemes.
+
+The `MultiAuthPlugin` allows combining two or more authentication approaches, such as JWT and Basic authentication.
+
+The `MultiAuthRuleBasedAuthorizationPlugin` is used when the `MultiAuthPlugin` is also in use, and combines the various roles defined for all plugins to determine the proper role assignment for the user account.
+
+For information on configuring these plugins, see the following sections:
+
+* xref:deployment-guide:basic-authentication-plugin.adoc#combining-basic-authentication-with-other-schemes[Combining Basic Authentication with Other Schemes]
+* xref:deployment-guide:rule-based-authorization-plugin.adoc#multiple-authorization-plugins[Multiple Authorization Plugins]
+
+
+*ZooKeeper chroot*
+
+It's now possible to create the ZooKeeper chroot at startup if it does not already exist.
+See the section xref:deployment-guide:zookeeper-ensemble.adoc#using-the-z-parameter-with-binsolr[Using the -z Parameter with bin/solr] for an example.
+
+*Other Changes*
+
+A few other minor changes are worth noting:
+
+* The `config-read` pre-defined permission now correctly governs access for various configuration-related APIs.
+See also xref:deployment-guide:rule-based-authorization-plugin.adoc#predefined-permissions[Predefined Permissions].
+* The S3BackupRepository supports configuring the AWS Profile, if necessary. See also xref:deployment-guide:backup-restore.adoc#s3backuprepository[S3BackupRepository].
+* Additionally, backups will now properly succeed after SPLITSHARD operations, and will correctly handle incremental backup purges.
+* SolrJ now supports uploading configsets.
+
+
+
+=== Solr 8.10
+
+See the https://cwiki.apache.org/confluence/display/SOLR/ReleaseNote8_10[8.10 Release Notes^]
+for an overview of the main new features of Solr 8.10.
+
+When upgrading to 8.10.x users should be aware of the following major changes from 8.9.
+
+*Schema Designer UI*
+
+A new screen has been added to the Admin UI that allows you to interactively design a Solr schema using your documents.
+
+The designer screen provides a safe environment for you to:
+
+* Upload or paste sample documents to identify fields.
+* Get a "first" guess at what Solr thinks the field types in the fields should be.
+* Edit fields, field types, dynamic fields, and supporting files.
+* See how a field's analysis will impact your text.
+* Test how schema changes will impact query-time behavior.
+* Save your changes to a configset to use with a new collection.
+
+See the section xref:indexing-guide:schema-designer.adoc[] for full details.
+
+*Backups in S3*
+
+Following the redesign of backups in Solr 8.8 that allowed storage of incremental backups in Google Cloud environments, Solr 8.10 provides support for storing backups in Amazon S3 buckets.
+
+See the section xref:deployment-guide:backup-restore.adoc#s3backuprepository[S3BackupRepository] for how to configure.
+
+*Security Admin UI*
+
+Solr's Admin UI also got a new screen to support management of users, roles, and permissions.
+
+The new UI works when authentication and/or authorization has been enabled with `bin/solr auth` or by manually installing a `security.json` file.
+Before this, it provides a warning that your Solr instance is unsecured.
+
+See the section xref:deployment-guide:security-ui.adoc[] for details.
+
+*Solr SQL Improvements*
+
+A number of improvements have been made in Solr's SQL functionality:
+
+* Support added for `LIKE`, `IS NOT NULL`, `IS NULL`, and wildcards (for simplistic `LIKE` functionality).
+* Two new aggregation functions, `COUNT(DISTINCT field)` and `APPROX_COUNT_DISTINCT(field)`, have been added.
+* Queries using an `ORDER BY` clause can support `OFFSET` and `FETCH` operations.
+* Multi-valued fields can now be returned.
+* User permissions have been simplified so access to query endpoints `/sql`, `/select`, and `/export` is sufficient for full access for all SQL queries.
+
+*shards.preference*
+
+A new option for the `shards.preference` parameter allows selection of nodes based on whether or not the replica is a leader.
+Now adding `shards.preference=replica.leader:false` will limit queries only to replicas which are not currently their shard's leader.
+
+See the section xref:deployment-guide:solrcloud-distributed-requests.adoc#shards-preference-parameter[shards.preference Parameter] for details and examples.
+
+*Metrics & Prometheus Exporter*
+
+A new `expr` option in the Metrics API allows for more advanced filtering of metrics based on regular expressions.
+See the section xref:deployment-guide:metrics-reporting.adoc#metrics-api[Metrics API] for examples.
+
+The Prometheus Exporter's default `solr-exporter.config` has been improved to use the new `expr` option in the Metrics API to get a smaller set of metrics.
+The default metrics exported still include most metrics, but the configuration will be easier to trim as needed.
+This should help provide performance improvements in busy clusters being monitored by Prometheus.
+
+*ZooKeeper Credentials*
+
+ZooKeeper credentials can now be stored in a file whose location is defined with a system property instead of being passed in plain-text.
+See xref:deployment-guide:zookeeper-access-control.adoc#out-of-the-box-credential-implementations[Out of the Box Credential Implementations] for how to set this up.
+
+=== Solr 8.9
+
+See the https://cwiki.apache.org/confluence/display/SOLR/ReleaseNote89[8.9 Release Notes^]
+for an overview of the main new features of Solr 8.9.
+
+When upgrading to 8.9.x users should be aware of the following major changes from 8.8.
+
+*Backup and Restore*
+
+Solr 8.9 introduces extensive changes to Solr's backup and restore support.
+
+A new backup format has been introduced in Solr 8.9 which replaces the previous snapshot-based backup.
+This new format enables ‘incremental’ backups.
+Repeated backups to a given location will take advantage of the data stored by their predecessors and will only operate on files that have changed since the previous backup.
+This is supported by default, simply by storing each backup file in the same location.
+
+The old and new formats are not compatible, although backups in the old format, a full snapshot of all files, can still be used to restore to Solr for the time-being.
+The old format is officially deprecated, and support for it is likely to be removed in Solr 9.0.
+
+For the time-being the old format can be created by defining a parameter `incremental=false`.
+Again, though, this support is likely to be removed in Solr 9.0.
+
+More documentation on backups is available at xref:deployment-guide:backup-restore.adoc[].
+
+New Collections API commands for backups:
+
+* LISTBACKUP: Lists information about each backup stored at the specified repository location.
+See xref:deployment-guide:collection-management.adoc#listbackup[List Backups] for more details.
+* DELETEBACKUP: Deletes specified backups from the repository.
+See xref:deployment-guide:collection-management.adoc#deletebackup[Delete Backups] for more details.
+
+A new option for backup repository is also available in 8.9, which is to use Google Cloud Storage (GCS).
+This is a module (located in `modules/gcs-repository`).
+See xref:deployment-guide:backup-restore.adoc#gcsbackuprepository[GCSBackupRepository] for configuration details.
+The Solr community is working to add support for S3 buckets in the near future.
+
+*Nested Docs*
+
+Child Doc Transformer's `childFilter` parameter no longer applies query syntax
+escaping because it's inconsistent with the rest of Solr and was limiting.
+This refers to `[child childFilter='field:value']`.
+There was no escaping here prior to 8.0 either.
+
+*Collapse and Expand*
+
+* BlockCollapse: If documents have been (or could be) indexed in a way where documents with the same collapse key have been indexed contiguously in the index, a new "block collapse" provides a significant speed improvement over traditional collapse.
++
+See xref:query-guide:collapse-and-expand-results.adoc#block-collapsing[Block Collapsing] for details.
+
+* Expand Null Groups: A new parameter `expand.nullGroup` allows an expanded group to be returned containing document with no value in the expanded field.
+See xref:query-guide:collapse-and-expand-results.adoc#expand-component[Expand Component] for details.
+
+*In-Place Updates*
+
+A new request parameter `update.partial.requireInPlace=true` allows telling Solr to "fail fast" if all of the necessary conditions are not satisfied to allow an in-place update to succeed.
+See also xref:indexing-guide:partial-document-updates.adoc#in-place-updates[In-Place Updates].
+
+*Metrics History*
+
+The Metrics History feature, which allowed long-term storage and aggregation of Solr's metrics, has been deprecated and will be removed in 9.0.
+
+*Embedded Solr Server*
+
+When using EmbeddedSolrServer, it will no longer close CoreContainer instances that were passed to it.
+
+=== Solr 8.8
+
+When upgrading to 8.8.x users should be aware of the following major changes from 8.7.
+
+*Nested Documents*
+
+* When doing atomic/partial updates to a child document:
+** Supply the `\_root_` field (the ID of the root document) so that Solr understands you are manipulating a child document and not a root document.
+In its absence, Solr looks at the `\_route_` parameter but this may change in the future because it's not an ideal substitute.
+If neither are present, Solr assumes you are updating a root document.
+If this assumption is false, Solr will do a cheap check that usually detects the problem and will
+throw an exception to alert you of the need to specify the Root ID.
+This backwards incompatible change was done to increase performance and robustness.
+** This feature no longer requires `stored=true` or `docValues=true` on the `\_root_` field.
+You might have it for other purposes though (e.g., for `uniqueBlock(...)`).
+** This feature no longer requires the `\_nest_path_` field, although you probably ought to
+continue to define it as it's useful for other things.
+
+*Removed Modules*
+
+* The search results clustering module (Carrot2) has been removed from 8.x Solr due to lack of Java 1.8 compatibility in the dependency that provides online clustering of search results.
+The module will be re-introduced in Solr 9.0.
+
+*Learning to Rank*
+
+* Interleaving support has been added to Learning to Rank (LTR).
+Currently only the Team Draft Interleaving algorithm is supported.
+For examples using this feature, see the section xref:query-guide:learning-to-rank.adoc#running-a-rerank-query-interleaving-two-models[Running a Rerank Query Interleaving Two Models].
+
+*Metrics*
+
+* Two metrics have been added for SolrCloud's Overseer:
+** `solr_metrics_overseer_stateUpdateQueueSize`
+** `solr_metrics_overseer_collectionWorkQueueSize`
+
+*Prometheus Exporter*
+
+* The `./bin` scripts included with the Prometheus Exporter now allow use of custom java options with environment variables.
+See the section xref:deployment-guide:monitoring-with-prometheus-and-grafana.adoc#environment-variable-options[Environment Variable Options] for more details.
+* The default Grafana dashboards now include panels for query performance monitoring.
+The default Prometheus Exporter configuration includes metrics like queries-per-second (QPS) and 95th percentiles (P95) to populate the new panels.
+* The default Prometheus Exporter configuration also includes the two new metrics mentioned in the Metrics above.
+
+*Solr Home*
+
+* The internal logic for identifying 'Solr Home' (`solr.solr.home`) has been refactored to make testing less error prone.
+Plugin developers using `SolrPaths.locateSolrHome()` or 'new `SolrResourceLoader`' should check deprecation warnings as existing some existing functionality will be removed in 9.0.
+https://issues.apache.org/jira/browse/SOLR-14934[SOLR-14934] has more technical details about this change for those concerned.
+
+*base_url removed from stored state*
+
+As of Solr 8.8.0, the `base_url` property was removed from the stored state for replicas (SOLR-12182).
+If you're able to upgrade SolrJ to 8.8.x
+for all of your client applications, then you can set `-Dsolr.storeBaseUrl=false` (introduced in Solr 8.8.1) to better align the stored state
+in ZooKeeper with future versions of Solr.
+However, if you are not able to upgrade SolrJ to 8.8.x for all client applications,
+then leave the default `-Dsolr.storeBaseUrl=true` so that Solr will continue to store the `base_url` in ZooKeeper.
+
+You may also see some NPE in collection state updates during a rolling upgrade to 8.8.0 from a previous version of Solr.
+After upgrading all nodes in your cluster
+to 8.8.0, collections should fully recover.
+Trigger another rolling restart if there are any replicas that do not recover after the upgrade to re-elect leaders.
+
+=== Solr 8.7
+
+See the https://cwiki.apache.org/confluence/display/SOLR/ReleaseNote87[8.7 Release Notes^]
+for an overview of the main new features of Solr 8.7.
+
+When upgrading to 8.7.x users should be aware of the following major changes from 8.6.
+
+*Autoscaling*
+
+* If upgrading from **8.6.0**, please see the <<Solr 8.6.1,8.6.1 Upgrade notes>> below for information on performance degradations introduced in 8.6.0 that require some intervention to resolve.
+If you are already on 8.6.1 or higher, you can ignore these instructions.
+
+*Deprecations*
+
+* The autoscaling framework is now formally deprecated and will be removed in Solr 9.0.
+The Solr community is working on pluggable API to replace this functionality, with the goal for it to be ready by the time 9.0 is released.
+Deprecations include: autoscaling policy, triggers, `withCollection` support, simulation framework, autoscaling suggestions tab in the UI, `autoAddReplicas` and `UTILIZENODE` command.
+
+* Similarly, rule-based replica placement strategy has been deprecated and will be replaced
+in Solr 9.0 by APIs for replica placement and cluster events, with plugin-based implementations.
+
+* Support for detecting spinning disks has been removed in LUCENE-9576.
+Corresponding
+`spins` metrics in Solr still exist but now they always return `false` and will be removed in Solr 9.0.
+
+*User-Managed Cluster Terminology Updated*
+
+* Solr has replaced the terms "master" and "slave" in the codebase and all documentation with "leader" and "follower".
++
+This functionality has only changed in terms of parameter names changed, and we do not expect any back-compatibility issues on upgrade to 8.7 or even 9.0 later.
++
+However, users should update their `solrconfig.xml` files after completing the upgrade on all nodes of a cluster.
+Comparing your configuration to the updated configuration examples in xref:deployment-guide:user-managed-index-replication.adoc[] will show examples of what needs to change, but here are the main changes:
++
+. On the replication leader, in the definition of the `/replication` request handler:
+.. Replace "master" with "leader".
+.. Replace "slave" with "follower" if the former term is used in the name of any follower `solrconfig.xml` file definitions.
+This file can be named anything, so you can change it to whatever you'd like to call it if you'd like.
+.. Replace "slave" with "follower" if the former term is used in a replication repeater configuration.
+. On the replication follower, in the definition of the `/replication` request handler:
+.. Replace "masterUrl" with "leaderUrl".
+.. Replace "slave" with "follower" if the former term is used in a repeater configuration.
+
+*JSON Facets*
+
+* Performance enhancements for the `relatedness()` statistics function are included with 8.7.
+These yield the highest benefits with high-cardinality fields and can be disabled if working with lower cardinality fields with a new `sweep_collection` parameter.
+See the section xref:query-guide:json-facet-api.adoc#relatedness-options[relatedness() Options] for details.
+
+*solr.in.sh / solr.in.cmd*
+
+* Solr has relied on the `SOLR_STOP_WAIT` parameter defined in `solr.in.sh` or `solr.in.cmd` to determine how long to wait on _startup_.
+A new parameter `SOLR_START_WAIT` allows defining how long Solr should wait for start up to complete.
++
+If the time set by this parameter is exceeded, Solr will exit the startup process and return the last few lines of the `solr.log` file to the terminal.
++
+By default, this parameter is set to the same value as `SOLR_STOP_WAIT`.
+
+* The default ZooKeeper client timeout (`ZK_CLIENT_TIMEOUT`) is now 30 seconds (`30000` milliseconds) instead of 15.
+
+*Configsets*
+
+* It's now possible to overwrite an existing configset when uploading changes by supplying the `overwrite=true` parameter to the xref:configuration-guide:configsets-api.adoc#configsets-upload[Configset API].
++
+A related parameter is `cleanup=true`, which allows deleting any files from the old configset that are left behind after the overwrite.
++
+The default for both of these parameters is `false`.
+
+* When deleting a collection that has an automatically created configset (i.e., the configset was copied from the `_default` collection when the collection was created), the configset will also be deleted if it is not in use by any other collection.
+
+*Logging*
+
+* A request ID (`rid`) is now logged for all distributed search requests (in SolrCloud) which can be used to correlate query events across the system.
+A parameter `disableRequestId=true` can be added to disable this if desired.
+
+=== Solr 8.6.1
+
+See the https://cwiki.apache.org/confluence/display/SOLR/ReleaseNote861[8.6.1 Release Notes^]
+for an overview of the fixes included in Solr 8.6.1.
+
+When upgrading to 8.6.1 users should be aware of the following major changes from 8.6.0.
+
+*Autoscaling*
+
+* As mentioned in the 8.6 upgrade notes, a default autoscaling policy was provided starting in 8.6.0.
+This default autoscaling policy resulted in increasingly slow collection creation calls in large clusters (50+ collections).
++
+In 8.6.1 the default autoscaling policy has been removed, and clusters will not use autoscaling unless a policy has explicitly been created.
+If your cluster is running 8.6.0 and *not using an explicit autoscaling policy*, upgrade to 8.6.1 and remove the default cluster policy and preferences via the following command.
++
+Replace `localhost:8983` with your Solr endpoint.
++
+[source,text]
+curl -X POST -H 'Content-type:application/json'  -d '{set-cluster-policy : [], set-cluster-preferences : []}' http://localhost:8983/api/cluster/autoscaling
++
+This information is only relevant for users upgrading from 8.6.0.
+If upgrading from an earlier version to 8.6.1+, this warning can be ignored.
+
+=== Solr 8.6
+
+See the https://cwiki.apache.org/confluence/display/SOLR/ReleaseNote86[8.6 Release Notes^]
+for an overview of the main new features of Solr 8.6.
+
+When upgrading to 8.6.x users should be aware of the following major changes from 8.5.
+
+*Support for Block-Max WAND*
+
+Lucene added support for Block-Max WAND in 8.0, and 8.6 makes this available for Solr also.
+
+This can provide significant performance enhancements by not calculating the score for results which are not likely to appear in the top set of results.
+
+It is enabled when using a new query parameter `minExactCount`.
+This parameter tells Solr to accurately count the number of hits accurately until at least this value.
+Once this value is reached, Solr can skip over documents that don't have a score high enough to be in the top set of documents, which has the potential for greatly speeding up searches.
+
+It's important to note that when using this parameter, the hit count of searches may not be accurate.
+It is guaranteed that the hit count is accurate up to the value of `minExactCount`, but any returned hit count higher than that may be an approximation.
+
+A new boolean attribute `numFoundExact` is included in all responses to indicate if the hit count in the response is expected to be exact or not.
+
+More information about this new feature is available in the section xref:query-guide:common-query-parameters.adoc#minexactcount-parameter[minExactCount Parameter].
+
+*Autoscaling*
+
+* **NOTE: The default autoscaling policy has been removed as of 8.6.1**
++
+Solr now includes a default autoscaling policy.
+This policy can be overridden with your custom rules or by specifying an empty policy to replace the default.
+
+* The ComputePlan action now supports a collection selector to identify collections based on collection properties to determine which collections should be operated on.
+
+*Security*
+
+* Prior to Solr 8.6 Solr APIs which take a file system location, such as core creation, backup, restore, and others, did not validate the path and Solr would allow any absolute or relative path.
+Starting in 8.6 only paths that are relative to `SOLR_HOME`, `SOLR_DATA_HOME` and `coreRootDir` are allowed by default.
++
+If you need to create a core or store a backup outside the default paths, you will need to tell Solr which paths to allow.
+A new element in `solr.xml` called `allowPaths` takes a comma-separated list of allowed paths.
++
+When using the `solr.xml` file that ships with 8.6, you can configure the list of paths to allow through the system property `solr.allowPaths`.
+Please see `bin/solr.in.sh` or `bin\solr.in.cmd` for example usage.
+Using the value `*` will allow any path as in earlier versions.
++
+For more on this, see the section xref:configuration-guide:configuring-solr-xml.adoc#the-solr-element[Solr.xml Parameters].
++
+Windows SMB shares on the UNC format, such as `\\myhost\myshare\mypath` are now always disallowed.
+Please use drive letter mounts instead, i.e., `S:\mypath`.
+
+* A new authorization plugin `ExternalRoleRuleBasedAuthorizationPlugin` is now available.
+This plugin allows an authentication plugin (such as JWT) to supply a user's roles instead of maintaining a user-to-role mapping inside Solr.
+
+* When authentication is enabled, the Admin UI Dashboard (main screen) now includes a panel that shows the authentication and authorization plugins in use, the logged in username, and the roles assigned to this user.
+A new link will also appear in the left-hand navigation to allow a user to log out.
+
+*Streaming Expressions*
+
+* The `/export` handler now supports streaming expressions to allow limiting the output of the export to only matching documents.
++
+For more information about how to use this, see the section xref:query-guide:exporting-result-sets.adoc#specifying-the-local-streaming-expression[Specifying the Local Streaming Expression].
+
+* The `stats`, `facet`, and `timeseries` expressions now support percentiles and standard deviation aggregations.
+
+*Highlighting*
+
+For the Unified Highlighter: The setting `hl.fragsizeIsMinimum` now defaults to `false` because `true` was found to be a significant performance regression when highlighting lots of text.
+This will yield longer highlights on average compared to Solr 8.5 but relatively unchanged compared to previous releases.
+Furthermore, if your application highlights lots of text, you may want to experiment with lowering `hl.fragAlignRatio` to trade ideal fragment alignment for better performance.
+
+*Deprecations*
+
+A primary focus of the community is improving Solr's stability and supportability.
+With the addition of the package manager system in 8.4, we now have the ability to move some features into plugins maintained by third-parties with the expertise to properly develop and support them.
+Our goal is to make running Solr easier and less prone to outages and other headaches.
+In this spirit, the following features have been deprecated and are slated to be removed in Solr 9.0.
+
+* Cross Data Center Replication (CDCR), in its current form, is deprecated and is scheduled to be removed in 9.0.
+This feature is unlikely to be replaced by an identical plugin.
+However, the community is working on figuring out a replacement feature for disaster recovery and failover.
+
+* The Data Import Handler (DIH) is deprecated and is scheduled to be removed in 9.0.
+Work to replace DIH with a community-supported plugin is underway and may be available soon.
+
+* Support to store indexes and backups in HDFS is deprecated and is scheduled to be removed in 9.0.
+A community-supported version of this may be available as a plugin in the future.
+For more details, please see https://issues.apache.org/jira/browse/SOLR-14021[SOLR-14021^].
+
+Users interested in maintaining a feature as a plugin are encouraged to join the https://solr.apache.org/community.html#mailing-lists-chat[developer mailing list^] to find out more about how to help.
+
+=== Solr 8.5
+
+See the https://cwiki.apache.org/confluence/display/SOLR/ReleaseNote85[8.5 Release Notes^]
+for an overview of the main new features of Solr 8.5.
+
+When upgrading to 8.5.x users should be aware of the following major changes from 8.4.
+
+__Note: an index incompatibility warning was retroactively added below to 8.4 for users choosing a non-default postings format (e.g., "FST50").__
+
+*Considerations for a SolrCloud Upgrade*
+
+Solr 8.5 introduces a change in the format used for the elements in the Overseer queues and maps (see https://issues.apache.org/jira/browse/SOLR-14095[SOLR-14095] for technical discussion of the change).
+This queue is used internally by the Overseer to reliably handle
+operations, to communicate operation results between the Overseer and the coordinator node, and by the REQUESTSTATUS API for displaying information about async Collection operations.
+
+This change won’t require you to change any client-side code you should see no differences on the client side.
+However, it does require some care when upgrading an existing SolrCloud cluster depending on your upgrade strategy.
+
+If you are upgrading Solr with an atomic restart strategy:
+
+* If you don’t use async or REQUESTSTATUS operations, you should be able to restart and not see any issues.
+* If you do use Collection API operations:
+. Pause Collection API operations.
+. Cleanup queues (See the section xref:configuration-guide:collections-api.adoc#deletestatus[DELETESTATUS] for examples)
+if you use async operations.
+. Upgrade and restart the nodes.
+. Resume all normal operations.
+
+If you are upgrading Solr with a rolling restart strategy:
+
+* If you don’t use Collection API operations, you should be able to do a rolling restart and not see
+any issues.
+* If you do use Collection API operations, but you can pause their use during the restart the easiest
+way is to:
+. Pause Collection API operations.
+. Upgrade and restart all nodes.
+. Cleanup queues (See the section xref:configuration-guide:collections-api.adoc#deletestatus[DELETESTATUS] for examples)
+if you use async operations.
+. Resume all normal operations.
+
+If you use Collection API operations and can’t pause them during the upgrade:
+
+. Start 8.5 nodes with the system property: `-Dsolr.useUnsafeOverseerResponse=deserialization`.
+Ensure the
+Overseer node is upgraded last.
+. Once all nodes are in 8.5 and once you don’t need to read old status anymore, restart again removing the
+system property.
+
+If you prefer to keep the old (but insecure) serialization strategy, you can start your nodes using the system
+property: `-Dsolr.useUnsafeOverseerResponse=true`.
+Keep in mind that this will be removed in future version of Solr.
+
+*Security Manager*
+
+Solr now has the ability to run with a Java security manager enabled.
+To enable this, set the property `SOLR_SECURITY_MANAGER_ENABLED=true` in `solr.in.sh` or `solr.in.cmd`.
+Note that if you are using HDFS to store indexes, you cannot enable the security manager.
+
+In Solr 9.0, this will be the default.
+
+// See SOLR-14147: See also the section xref:deployment-guide:securing-solr.adoc#enable-security-manager[Enable Security Manager].
+
+*Block/Allow Specific IPs*
+
+Solr has two new parameters to allow you to restrict access to Solr using IP addresses.
+Use `SOLR_IP_WHITELIST` to configure a whitelist, and `SOLR_IP_BLACKLIST` to configure a blacklist.
+These properties are defined in `solr.in.sh` or `solr.in.cmd`.
+
+See also the section xref:deployment-guide:securing-solr.adoc#ip-access-control[Enable IP Access Control].
+
+*BlockJoin Facet Deprecation*
+
+The BlockJoinFacetComponent is marked for deprecation and will be removed in 9.0.
+Users are encouraged to migrate to `uniqueBlock()` in JSON Facet API.
+More information about this is available in the section xref:query-guide:json-faceting-domain-changes.adoc#block-join-domain-changes[Block Join Domain Changes].
+
+*Caching with the Boolean Query Parser*
+
+By default, the xref:query-guide:other-parsers.adoc#boolean-query-parser[Boolean Query Parser] caches queries in Solr's filterCache.
+It's now possible to disable this with the local param `cache=false`.
+
+*Indexing Log Files*
+
+Solr now includes a command line tool, `bin/postlogs` which will index Solr's log files into a collection.
+This provides an easy way to use Solr or visualization tools (such as Zeppelin) to troubleshoot problems with the system.
+
+See the documentation for more details at xref:query-guide:logs.adoc[].
+
+*Highlighting*
+
+Solr's Unified Highlighter now has two parameters to help control passage sizing, `hl.fragAlignRatio` and `hl.fragsizeIsMinimum`.
+See the section xref:query-guide:highlighting.adoc#unified-highlighter[Unified Highlighter] for details about these new parameters.
+Regardless of the settings, the passages may be sized differently than before.
+_Warning: These default settings were found to be a significant performance regression for apps that highlight lots of text with the default sentence break iterator.
+See the 8.6 upgrade notes for advise you can apply in 8.5._
+
+*Shared Library System Parameter*
+
+Solr's `solr.xml` file has long had support for a `sharedLib` parameter, which allows you to define a common location for .jar files that may need to be in the path for all cores.
+
+This property can now be defined in `solr.in.sh` or `solr.in.cmd` as a system property (`-Dsolr.sharedLib=/path/to/lib`) added to `SOLR_OPTS` (see `solr.in.sh` or `solr.in.cmd` for details).
+
+=== Solr 8.4
+
+See the https://cwiki.apache.org/confluence/display/SOLR/ReleaseNote84[8.4 Release Notes^]
+for an overview of the main new features of Solr 8.4.
+
+When upgrading to 8.4.x users should be aware of the following major changes from 8.3.
+
+*Reminder:*  If you set the `postingsFormat` or `docValuesFormat` in the schema in order to use a non-default option, you risk preventing yourself from upgrading your Lucene/Solr software at future versions.
+Multiple non-default postings formats changed in 8.4, thus rendering the index data from a previous index.
+This includes "FST50" which was recommended by the Solr TaggerHandler for performance reasons.
+There is now improved documentation to navigate this trade-off choice.
+
+*Package Management System*
+
+Version 8.4 introduces a package management system to Solr.
+The goals of the
+system are to allow hot (live) deployment of plugins, provide packaging
+guidelines for plugins, and standardize Solr's approach by following familiar
+concepts used in other package management systems.
+
+The system is designed to eventually replace use of the `<lib ../>` directive,
+the Blob Store, and other methods of deploying plugins and custom components
+to Solr.
+
+The system is currently considered experimental, so use with caution.
+It must
+be enabled with a system parameter passed at start up before it can be used.
+For details, please see the section xref:configuration-guide:package-manager.adoc[].
+
+With this feature Solr's Blob Store functionality is now deprecated and will likely be removed in 9.0.
+
+*Security*
+
+The follow mix of changes were all made with the intention of making Solr more secure out of the box.
+
+* The `solrconfig.xml` file in Solr's `_default` configset has been trimmed of
+the following previously pre-configured items:
++
+** All `<lib .../>` directives.
+This means that Solr Cell (aka Tika), Learning
+to Rank, Clustering (with Carrot2), language identification, and Velocity (for
+the `/browse` sample search interface) are no longer enabled out of the box.
+** The `/browse`, `/tvrh`, and `/update/extract` request handlers.
+** The Term Vector Component.
+** The XSLT and Velocity response writers.
++
+All of these items can be added to your Solr implementation by manually editing
+`solrconfig.xml` to add them back in, or use the xref:configuration-guide:config-api.adoc[].
++
+The `sample_techproducts_configs` and the examples found in `./example` are unchanged.
+
+* Configsets that have been uploaded with an unsecured Configset API (i.e., when authentication is not enabled) are considered "Untrusted Configsets".
++
+In order to bolster Solr's out-of-the-box security, these untrusted configsets
+are no longer allowed to use the `<lib .../>` directive to implement modules
+or custom Jars.
++
+When upgrading to 8.4, if you are using untrusted configsets that contain `<lib ../>`
+directives, their corresponding collections will not load (they will cease to
+work).
+You have a few options in this case:
+
+** You can secure your Solr instance with xref:deployment-guide:authentication-and-authorization-plugins.adoc[authentication] and re-upload the configset (using the `bin/solr zk upconfig ...` xref:deployment-guide:solr-control-script-reference.adoc[Solr CLI] command);
+** You can put your custom Jars in Solr's classpath instead of `lib` directories;
+** You can try the new package management system to manage your custom Jars.
++
+See the section xref:configuration-guide:configsets-api.adoc#configsets-upload[Upload a Configset] for more details about trusted vs. untrusted configsets.
+
+* Our default Jetty configuration has been updated to now set a
+Content-Security-Policy (CSP) by default.
+See `./server/etc/jetty.xml` for
+details about how it is configured.
++
+As a result of this change, any custom HTML served by Solr's HTTP server that contains inline Javascript will no longer execute in modern browsers.
+The options for you are:
+
+** Change your JavaScript code to not run inline any longer;
+** Edit `jetty.xml` to remove CSP (creating weaker security protection);
+** Remove/alter the headers with a reverse proxy.
+
+* Solr's Blob Store and runtime libs functionality are now deprecated and are planned to be removed from Solr in version 9.0.
+It has been replaced with the new package management system.
+
+* The Velocity response writer is also now deprecated and is planned to be removed from Solr in version 9.0.
+
+*Using Collapse with Group Disallowed*
+
+Using the xref:query-guide:collapse-and-expand-results.adoc[CollapsingQueryParser] with xref:query-guide:result-grouping.adoc[] has never been supported as it causes inconsistent behavior and NullPointerException errors.
+We have now explicitly disallowed this combination to prevent these errors.
+If you are using these together, you will need to modify your queries.
+
+*SolrJ*
+
+* SolrJ now supports the `shards.preference` parameter for single-shard
+scenarios to ensure multi-shard and single-shard request routing works in the same way.
++
+See xref:deployment-guide:solrj.adoc#cloud-request-routing[Cloud Request Routing] and xref:deployment-guide:solrcloud-distributed-requests.adoc#shards-preference-parameter[shards.preference Parameter] for details.
+
+* `QueryResponse.getExplainMap()` type has changed from `Map<String, String>` to `Map<String, Object>` in order to support structured explanations.
++
+This change is expected to be mostly back-compatible.
+Compiled third-party
+components will work the same due to type erasure, but source code changes may
+be required.
+
+* Replica routing code has been moved to SolrJ, making those classes available
+to clients if necessary.
+
+*Streaming Expressions*
+
+* A new DBSCAN clustering streaming evaluator has been added.
+
+* The `precision` stream evaluator can now operate on matrices.
+
+* The `random` streaming expression can now create the x-axis.
+
+*JSON Facets*
+
+* Two new aggregations have been added: `missing` and `countvals`.
+
+* Several aggregations now support multi-valued fields: `min`, `max`, `avg`, `sum`, `sumsq`, `stddev`, `variance`, and `percentile`.
+
+*Caches*
+
+* After the addition of `CaffeineCache` in 8.3, legacy SolrCache
+implementations are deprecated and likely to be removed in 9.0.
++
+Users are encouraged to transition their cache configurations to use
+`org.apache.solr.search.CaffeineCache` as soon as feasible.
+
+=== Solr 8.3
+
+See the https://cwiki.apache.org/confluence/display/SOLR/ReleaseNote83[8.3 Release Notes^] for an overview of the main new features of Solr 8.3.
+
+When upgrading to 8.3.x users should be aware of the following major changes from 8.2.
+
+*JWT Authentication*
+
+JWT Authentication now supports multiple identity providers.
+To allow this, the parameter `jwkUrl` has been deprecated and replaced with `jwksUrl`.
+Implementations using `jwkUrl` will continue to work as normal, but users
+should plan to transition their configurations to use `jwksUrl` instead as
+soon as feasible.
+
+*Caches*
+
+* Solr has a new cache implementation, `CaffeineCache`, which is now recommended over other caches.
+This cache is expected to generally provide most users lower memory footprint, higher hit ratio, and better multi-threaded performance.
++
+Since caching has a direct impact on the performance of your Solr
+implementation, before switching to any new cache implementation in
+production, take care to test for your environment and traffic patterns so
+you fully understand the ramifications of the change.
+
+* A new parameter, `maxIdleTime`, allows automatic eviction of cache items that have not been used in the defined amount of time.
+This allows the cache to release some memory and should aid those who want or need to fine-tune their caches.
+
+See the section xref:configuration-guide:caches-warming.adoc[] for more details about these and other cache options and parameters.
+
+=== Solr 8.2
+
+See the https://cwiki.apache.org/confluence/display/SOLR/ReleaseNote82[8.2 Release Notes^] for an overview of the main new features of Solr 8.2.
+
+When upgrading to 8.2.x, users should be aware of the following major changes from v8.1.
+
+*ZooKeeper 3.5.5*
+
+Solr 8.2 updates the version of ZooKeeper included with Solr to v3.5.5.
+
+It is recommended that external ensembles set up to work with Solr also be updated to ZooKeeper 3.5.5.
+
+This ZooKeeper release includes many new security features.
+In order for Solr's Admin UI to work with 3.5.5, the `zoo.cfg` file must allow access to ZooKeeper's "four-letter commands".
+At a minimum, `ruok`, `conf`, and `mntr` must be enabled, but other commands can optionally be enabled if you choose.
+See the section xref:deployment-guide:zookeeper-ensemble.adoc#configuration-for-a-zookeeper-ensemble[Configuration for a ZooKeeper Ensemble] for details.
+
+[WARNING]
+Until 8.3, https://issues.apache.org/jira/browse/SOLR-13672[SOLR-13672] causes the ZK Status screen in the Admin UI to not be able to report status.
+This only impacts the UI, ZooKeeper still operates correctly.
+
+*Routed Aliases*
+
+* Routed aliases now use collection properties to identify collections that belong to the alias; prior to 8.2, these aliases used core properties.
++
+This is backward-compatible and aliases created with prior versions will
+continue to work.
+However, new collections will no longer add the
+`routedAliasName` property to the `core.properties` file so any external code
+depending on this location will need to be updated.
+
+// TODO: aliases.adoc still says this is per-core?
+
+* Time-routed aliases now include a `TRA` infix in the collection name, in the pattern `<alias>_TRA_<timestamp>`. +
+Collections created with older versions will continue to work.
+
+*Distributed Tracing Support*
+
+This release adds support for tracing requests in Solr.
+Please review the section xref:deployment-guide:distributed-tracing.adoc[] for details on how to configure this feature.
+
+=== Solr 8.1
+
+See the https://cwiki.apache.org/confluence/display/SOLR/ReleaseNote810[8.1 Release Notes^] for an overview of the main new features of Solr 8.1.
+
+When upgrading to 8.1.x, users should be aware of the following major changes from v8.0.
+
+*Global maxBooleanClauses Parameter*
+
+* The behavior of the `maxBooleanClauses` parameter has changed to reduce the risk of exponential query expansion when dealing with pathological query strings.
++
+A default upper limit of 1024 clauses is now enforced at the node level.
+This was the default prior to 7.0, and it can be overridden with a new global parameter in `solr.xml`.
+This limit will be enforced for all queries whether explicitly defined by the user (or client), or created by Solr and Lucene internals.
++
+An identical parameter is available in `solrconfig.xml` for limiting the size of queries explicitly defined by the user (or client), but this per-collection limit will still be restricted by the global limit set in `solr.xml`.
++
+If your use case demands that you a lot of OR or AND clauses in your queries, upon upgrade to 8.1 you may need to adjust the global `maxBooleanClauses` parameter since between 7.0 and 8.1 the limit was effectively unbounded.
++
+For more information about the new parameter, see the section xref:configuration-guide:configuring-solr-xml.adoc#global-maxbooleanclauses[maxBooleanClauses].
+
+*Security*
+
+* JSON Web Tokens (JWT) are now supported for authentication.
+These allow Solr to assert a user is already authenticated via an external identity provider, such as an OpenID Connect-enabled IdP.
+For more information, see the section xref:deployment-guide:jwt-authentication-plugin.adoc[].
+
+* A new security plugin for audit logging has been added.
+A default class `SolrLogAuditLoggerPlugin` is available and configurable in `security.json`.
+The base class is also extendable for adding custom audit plugins if needed.
+See the section xref:deployment-guide:audit-logging.adoc[] for more information.
+
+*Collections API*
+
+* The output of the REQUESTSTATUS command in the Collections API will now include internal asynchronous requests (if any) in the "success" or "failed" keys.
+
+* The CREATE command will now return the appropriate status code (4xx, 5xx, etc.) when the command has failed.
+Previously, it always returned `0`, even in failure.
+
+* The MODIFYCOLLECTION command now accepts an attribute to set a collection as read-only.
+This can be used to block a collection from receiving any updates while still allowing queries to be served.
+See the section xref:deployment-guide:collection-management.adoc#modifycollection[MODIFYCOLLECTION] for details on how to use it.
+
+* A new command RENAME allows renaming a collection by setting up a one-to-one alias using the new name.
+For more information, see the section xref:deployment-guide:collection-management.adoc#rename[RENAME].
+
+* A new command REINDEXCOLLECTION allows indexing existing stored fields from a source collection into a new collection.
+For more information, please see the section xref:deployment-guide:collection-management.adoc#reindexcollection[REINDEXCOLLECTION].
+
+*Logging*
+
+* The default Log4j2 logging mode has been changed from synchronous to asynchronous.
+This will improve logging throughput and reduce system contention at the cost of a _slight_ chance that some logging messages may be missed in the event of abnormal Solr termination.
++
+If even this slight risk is unacceptable, the Log4j configuration file found in `server/resources/log4j2.xml` has the synchronous logging configuration in a commented section and can be edited to re-enable synchronous logging.
+
+*Metrics*
+
+* The SolrGangliaReporter has been removed from Solr.
+The metrics library used by Solr, Dropwizard Metrics, was updated to version 4, and Ganglia support was removed from it due to a dependency on the LGPL license.
+
+*Browse UI (Velocity)*
+
+* Velocity and Velocity Tools were both upgraded as part of this release.
+Velocity upgraded from 1.7 to 2.0.
+Please see https://velocity.apache.org/engine/2.0/upgrading.html about upgrading.
+Velocity Tools upgraded from 2.0 to 3.0.
+For more details, please see https://velocity.apache.org/tools/3.0/upgrading.html for details about the upgrade.
+
+*Default Garbage Collector (GC)*
+
+* Solr's default GC has been changed from CMS to G1.
+If you prefer to use CMS or any other GC method, you can modify the `GC_TUNE` section of `solr.in.sh` (*nix) or `solr.in.cmd` (Windows).
diff --git a/solr/solr-ref-guide/modules/upgrade-notes/pages/solr-upgrade-notes.adoc b/solr/solr-ref-guide/modules/upgrade-notes/pages/solr-upgrade-notes.adoc
index 617cd14a0e7..2b71cee817b 100644
--- a/solr/solr-ref-guide/modules/upgrade-notes/pages/solr-upgrade-notes.adoc
+++ b/solr/solr-ref-guide/modules/upgrade-notes/pages/solr-upgrade-notes.adoc
@@ -31,830 +31,27 @@ When planning your Solr upgrade, consider the customizations you have made to
 your system and review the {solr-javadocs}/changes/Changes.html[`CHANGES.txt`]
 file found in your Solr package.
 That file includes all the changes and updates
-that may effect your existing implementation.
+that may affect your existing implementation.
 
 Detailed steps for upgrading a Solr cluster are in the section xref:deployment-guide:upgrading-a-solr-cluster.adoc[].
 
-== Upgrading to 9.x Releases (NOT RELEASED)
+== Upgrading to 9.0 from 8.x Releases
 
-// DEVS: please put 9.0 Upgrade Notes in `major-changes-in-solr-9.adoc`!.
-
-== Upgrading to 8.x Releases
-
-If you are upgrading from 7.x, see the section <<Upgrading from 7.x Releases>> below.
-
-=== Solr 8.11
-
-See the https://cwiki.apache.org/confluence/display/SOLR/Release+Notes+8.11[8.11 Release Notes^]
-for an overview of the main new features of Solr 8.11.
-
-When upgrading to 8.11.x users should be aware of the following major changes from 8.10.
-
-*Support for Multiple Authentication Schemes*
-
-Two new authentication and authorization plugins provide support for configuring multiple authentication schemes.
-
-The `MultiAuthPlugin` allows combining two or more authentication approaches, such as JWT and Basic authentication.
-
-The `MultiAuthRuleBasedAuthorizationPlugin` is used when the `MultiAuthPlugin` is also in use, and combines the various roles defined for all plugins to determine the proper role assignment for the user account.
-
-For information on configuring these plugins, see the following sections:
-
-* xref:deployment-guide:basic-authentication-plugin.adoc#combining-basic-authentication-with-other-schemes[Combining Basic Authentication with Other Schemes]
-* xref:deployment-guide:rule-based-authorization-plugin.adoc#multiple-authorization-plugins[Multiple Authorization Plugins]
-
-
-*ZooKeeper chroot*
-
-It's now possible to create the ZooKeeper chroot at startup if it does not already exist.
-See the section xref:deployment-guide:zookeeper-ensemble.adoc#using-the-z-parameter-with-binsolr[Using the -z Parameter with bin/solr] for an example.
-
-*Other Changes*
-
-A few other minor changes are worth noting:
-
-* The `config-read` pre-defined permission now correctly governs access for various configuration-related APIs.
-See also xref:deployment-guide:rule-based-authorization-plugin.adoc#predefined-permissions[Predefined Permissions].
-* The S3BackupRepository supports configuring the AWS Profile, if necessary. See also xref:deployment-guide:backup-restore.adoc#s3backuprepository[S3BackupRepository].
-* Additionally, backups will now properly succeed after SPLITSHARD operations, and will correctly handle incremental backup purges.
-* SolrJ now supports uploading configsets.
-
-
-
-=== Solr 8.10
-
-See the https://cwiki.apache.org/confluence/display/SOLR/ReleaseNote8_10[8.10 Release Notes^]
-for an overview of the main new features of Solr 8.10.
-
-When upgrading to 8.10.x users should be aware of the following major changes from 8.9.
-
-*Schema Designer UI*
-
-A new screen has been added to the Admin UI that allows you to interactively design a Solr schema using your documents.
-
-The designer screen provides a safe environment for you to:
-
-* Upload or paste sample documents to identify fields.
-* Get a "first" guess at what Solr thinks the field types in the fields should be.
-* Edit fields, field types, dynamic fields, and supporting files.
-* See how a field's analysis will impact your text.
-* Test how schema changes will impact query-time behavior.
-* Save your changes to a configset to use with a new collection.
-
-See the section xref:indexing-guide:schema-designer.adoc[] for full details.
-
-*Backups in S3*
-
-Following the redesign of backups in Solr 8.8 that allowed storage of incremental backups in Google Cloud environments, Solr 8.10 provides support for storing backups in Amazon S3 buckets.
-
-See the section xref:deployment-guide:backup-restore.adoc#s3backuprepository[S3BackupRepository] for how to configure.
-
-*Security Admin UI*
-
-Solr's Admin UI also got a new screen to support management of users, roles, and permissions.
-
-The new UI works when authentication and/or authorization has been enabled with `bin/solr auth` or by manually installing a `security.json` file.
-Before this, it provides a warning that your Solr instance is unsecured.
-
-See the section xref:deployment-guide:security-ui.adoc[] for details.
-
-*Solr SQL Improvements*
-
-A number of improvements have been made in Solr's SQL functionality:
-
-* Support added for `LIKE`, `IS NOT NULL`, `IS NULL`, and wildcards (for simplistic `LIKE` functionality).
-* Two new aggregation functions, `COUNT(DISTINCT field)` and `APPROX_COUNT_DISTINCT(field)`, have been added.
-* Queries using an `ORDER BY` clause can support `OFFSET` and `FETCH` operations.
-* Multi-valued fields can now be returned.
-* User permissions have been simplified so access to query endpoints `/sql`, `/select`, and `/export` is sufficient for full access for all SQL queries.
-
-*shards.preference*
-
-A new option for the `shards.preference` parameter allows selection of nodes based on whether or not the replica is a leader.
-Now adding `shards.preference=replica.leader:false` will limit queries only to replicas which are not currently their shard's leader.
-
-See the section xref:deployment-guide:solrcloud-distributed-requests.adoc#shards-preference-parameter[shards.preference Parameter] for details and examples.
-
-*Metrics & Prometheus Exporter*
-
-A new `expr` option in the Metrics API allows for more advanced filtering of metrics based on regular expressions.
-See the section xref:deployment-guide:metrics-reporting.adoc#metrics-api[Metrics API] for examples.
-
-The Prometheus Exporter's default `solr-exporter.config` has been improved to use the new `expr` option in the Metrics API to get a smaller set of metrics.
-The default metrics exported still include most metrics, but the configuration will be easier to trim as needed.
-This should help provide performance improvements in busy clusters being monitored by Prometheus.
-
-*ZooKeeper Credentials*
-
-ZooKeeper credentials can now be stored in a file whose location is defined with a system property instead of being passed in plain-text.
-See xref:deployment-guide:zookeeper-access-control.adoc#out-of-the-box-credential-implementations[Out of the Box Credential Implementations] for how to set this up.
-
-=== Solr 8.9
-
-See the https://cwiki.apache.org/confluence/display/SOLR/ReleaseNote89[8.9 Release Notes^]
-for an overview of the main new features of Solr 8.9.
-
-When upgrading to 8.9.x users should be aware of the following major changes from 8.8.
-
-*Backup and Restore*
-
-Solr 8.9 introduces extensive changes to Solr's backup and restore support.
-
-A new backup format has been introduced in Solr 8.9 which replaces the previous snapshot-based backup.
-This new format enables ‘incremental’ backups.
-Repeated backups to a given location will take advantage of the data stored by their predecessors and will only operate on files that have changed since the previous backup.
-This is supported by default, simply by storing each backup file in the same location.
-
-The old and new formats are not compatible, although backups in the old format, a full snapshot of all files, can still be used to restore to Solr for the time-being.
-The old format is officially deprecated, and support for it is likely to be removed in Solr 9.0.
-
-For the time-being the old format can be created by defining a parameter `incremental=false`.
-Again, though, this support is likely to be removed in Solr 9.0.
-
-More documentation on backups is available at xref:deployment-guide:backup-restore.adoc[].
-
-New Collections API commands for backups:
-
-* LISTBACKUP: Lists information about each backup stored at the specified repository location.
-See xref:deployment-guide:collection-management.adoc#listbackup[List Backups] for more details.
-* DELETEBACKUP: Deletes specified backups from the repository.
-See xref:deployment-guide:collection-management.adoc#deletebackup[Delete Backups] for more details.
-
-A new option for backup repository is also available in 8.9, which is to use Google Cloud Storage (GCS).
-This is a module (located in `modules/gcs-repository`).
-See xref:deployment-guide:backup-restore.adoc#gcsbackuprepository[GCSBackupRepository] for configuration details.
-The Solr community is working to add support for S3 buckets in the near future.
-
-*Nested Docs*
-
-Child Doc Transformer's `childFilter` parameter no longer applies query syntax
-escaping because it's inconsistent with the rest of Solr and was limiting.
- This refers to `[child childFilter='field:value']`.
-There was no escaping here prior to 8.0 either.
-
-*Collapse and Expand*
-
-* BlockCollapse: If documents have been (or could be) indexed in a way where documents with the same collapse key have been indexed contiguously in the index, a new "block collapse" provides a significant speed improvement over traditional collapse.
-+
-See xref:query-guide:collapse-and-expand-results.adoc#block-collapsing[Block Collapsing] for details.
-
-* Expand Null Groups: A new parameter `expand.nullGroup` allows an expanded group to be returned containing document with no value in the expanded field.
-See xref:query-guide:collapse-and-expand-results.adoc#expand-component[Expand Component] for details.
-
-*In-Place Updates*
-
-A new request parameter `update.partial.requireInPlace=true` allows telling Solr to "fail fast" if all of the necessary conditions are not satisfied to allow an in-place update to succeed.
-See also xref:indexing-guide:partial-document-updates.adoc#in-place-updates[In-Place Updates].
-
-*Metrics History*
-
-The Metrics History feature, which allowed long-term storage and aggregation of Solr's metrics, has been deprecated and will be removed in 9.0.
-
-*Embedded Solr Server*
-
-When using EmbeddedSolrServer, it will no longer close CoreContainer instances that were passed to it.
-
-=== Solr 8.8
-
-When upgrading to 8.8.x users should be aware of the following major changes from 8.7.
-
-*Nested Documents*
-
-* When doing atomic/partial updates to a child document:
-** Supply the `\_root_` field (the ID of the root document) so that Solr understands you are manipulating a child document and not a root document.
-In its absence, Solr looks at the `\_route_` parameter but this may change in the future because it's not an ideal substitute.
-If neither are present, Solr assumes you are updating a root document.
-If this assumption is false, Solr will do a cheap check that usually detects the problem and will
-throw an exception to alert you of the need to specify the Root ID.
-This backwards incompatible change was done to increase performance and robustness.
-** This feature no longer requires `stored=true` or `docValues=true` on the `\_root_` field.
-You might have it for other purposes though (e.g., for `uniqueBlock(...)`).
-** This feature no longer requires the `\_nest_path_` field, although you probably ought to
-continue to define it as it's useful for other things.
-
-*Removed Modules*
-
-* The search results clustering module (Carrot2) has been removed from 8.x Solr due to lack of Java 1.8 compatibility in the dependency that provides online clustering of search results.
-The module will be re-introduced in Solr 9.0.
-
-*Learning to Rank*
-
-* Interleaving support has been added to Learning to Rank (LTR).
-Currently only the Team Draft Interleaving algorithm is supported.
-For examples using this feature, see the section xref:query-guide:learning-to-rank.adoc#running-a-rerank-query-interleaving-two-models[Running a Rerank Query Interleaving Two Models].
-
-*Metrics*
-
-* Two metrics have been added for SolrCloud's Overseer:
-** `solr_metrics_overseer_stateUpdateQueueSize`
-** `solr_metrics_overseer_collectionWorkQueueSize`
-
-*Prometheus Exporter*
-
-* The `./bin` scripts included with the Prometheus Exporter now allow use of custom java options with environment variables.
-See the section xref:deployment-guide:monitoring-with-prometheus-and-grafana.adoc#environment-variable-options[Environment Variable Options] for more details.
-* The default Grafana dashboards now include panels for query performance monitoring.
-The default Prometheus Exporter configuration includes metrics like queries-per-second (QPS) and 95th percentiles (P95) to populate the new panels.
-* The default Prometheus Exporter configuration also includes the two new metrics mentioned in the Metrics above.
-
-*Solr Home*
-
-* The internal logic for identifying 'Solr Home' (`solr.solr.home`) has been refactored to make testing less error prone.
-Plugin developers using `SolrPaths.locateSolrHome()` or 'new `SolrResourceLoader`' should check deprecation warnings as existing some existing functionality will be removed in 9.0.
-https://issues.apache.org/jira/browse/SOLR-14934[SOLR-14934] has more technical details about this change for those concerned.
-
-*base_url removed from stored state*
-
-As of Solr 8.8.0, the `base_url` property was removed from the stored state for replicas (SOLR-12182).
-If you're able to upgrade SolrJ to 8.8.x
-for all of your client applications, then you can set `-Dsolr.storeBaseUrl=false` (introduced in Solr 8.8.1) to better align the stored state
-in ZooKeeper with future versions of Solr.
-However, if you are not able to upgrade SolrJ to 8.8.x for all client applications,
-then leave the default `-Dsolr.storeBaseUrl=true` so that Solr will continue to store the `base_url` in ZooKeeper.
-
-You may also see some NPE in collection state updates during a rolling upgrade to 8.8.0 from a previous version of Solr.
-After upgrading all nodes in your cluster
-to 8.8.0, collections should fully recover.
-Trigger another rolling restart if there are any replicas that do not recover after the upgrade to re-elect leaders.
-
-=== Solr 8.7
-
-See the https://cwiki.apache.org/confluence/display/SOLR/ReleaseNote87[8.7 Release Notes^]
-for an overview of the main new features of Solr 8.7.
-
-When upgrading to 8.7.x users should be aware of the following major changes from 8.6.
-
-*Autoscaling*
-
-* If upgrading from **8.6.0**, please see the <<Solr 8.6.1,8.6.1 Upgrade notes>> below for information on performance degradations introduced in 8.6.0 that require some intervention to resolve.
-If you are already on 8.6.1 or higher, you can ignore these instructions.
-
-*Deprecations*
-
-* The autoscaling framework is now formally deprecated and will be removed in Solr 9.0.
-The Solr community is working on pluggable API to replace this functionality, with the goal for it to be ready by the time 9.0 is released.
-Deprecations include: autoscaling policy, triggers, `withCollection` support, simulation framework, autoscaling suggestions tab in the UI, `autoAddReplicas` and `UTILIZENODE` command.
-
-* Similarly, rule-based replica placement strategy has been deprecated and will be replaced
-  in Solr 9.0 by APIs for replica placement and cluster events, with plugin-based implementations.
-
-* Support for detecting spinning disks has been removed in LUCENE-9576.
-Corresponding
-`spins` metrics in Solr still exist but now they always return `false` and will be removed in Solr 9.0.
-
-*User-Managed Cluster Terminology Updated*
-
-* Solr has replaced the terms "master" and "slave" in the codebase and all documentation with "leader" and "follower".
-+
-This functionality has only changed in terms of parameter names changed, and we do not expect any back-compatibility issues on upgrade to 8.7 or even 9.0 later.
-+
-However, users should update their `solrconfig.xml` files after completing the upgrade on all nodes of a cluster.
-Comparing your configuration to the updated configuration examples in xref:deployment-guide:user-managed-index-replication.adoc[] will show examples of what needs to change, but here are the main changes:
-+
-. On the replication leader, in the definition of the `/replication` request handler:
-.. Replace "master" with "leader".
-.. Replace "slave" with "follower" if the former term is used in the name of any follower `solrconfig.xml` file definitions.
-This file can be named anything, so you can change it to whatever you'd like to call it if you'd like.
-.. Replace "slave" with "follower" if the former term is used in a replication repeater configuration.
-. On the replication follower, in the definition of the `/replication` request handler:
-.. Replace "masterUrl" with "leaderUrl".
-.. Replace "slave" with "follower" if the former term is used in a repeater configuration.
-
-*JSON Facets*
-
-* Performance enhancements for the `relatedness()` statistics function are included with 8.7.
-These yield the highest benefits with high-cardinality fields and can be disabled if working with lower cardinality fields with a new `sweep_collection` parameter.
-See the section xref:query-guide:json-facet-api.adoc#relatedness-options[relatedness() Options] for details.
-
-*solr.in.sh / solr.in.cmd*
-
-* Solr has relied on the `SOLR_STOP_WAIT` parameter defined in `solr.in.sh` or `solr.in.cmd` to determine how long to wait on _startup_.
-A new parameter `SOLR_START_WAIT` allows defining how long Solr should wait for start up to complete.
-+
-If the time set by this parameter is exceeded, Solr will exit the startup process and return the last few lines of the `solr.log` file to the terminal.
-+
-By default, this parameter is set to the same value as `SOLR_STOP_WAIT`.
-
-* The default ZooKeeper client timeout (`ZK_CLIENT_TIMEOUT`) is now 30 seconds (`30000` milliseconds) instead of 15.
-
-*Configsets*
-
-* It's now possible to overwrite an existing configset when uploading changes by supplying the `overwrite=true` parameter to the xref:configuration-guide:configsets-api.adoc#configsets-upload[Configset API].
-+
-A related parameter is `cleanup=true`, which allows deleting any files from the old configset that are left behind after the overwrite.
-+
-The default for both of these parameters is `false`.
-
-* When deleting a collection that has an automatically created configset (i.e., the configset was copied from the `_default` collection when the collection was created), the configset will also be deleted if it is not in use by any other collection.
-
-*Logging*
-
-* A request ID (`rid`) is now logged for all distributed search requests (in SolrCloud) which can be used to correlate query events across the system.
-A parameter `disableRequestId=true` can be added to disable this if desired.
-
-=== Solr 8.6.1
-
-See the https://cwiki.apache.org/confluence/display/SOLR/ReleaseNote861[8.6.1 Release Notes^]
-for an overview of the fixes included in Solr 8.6.1.
-
-When upgrading to 8.6.1 users should be aware of the following major changes from 8.6.0.
-
-*Autoscaling*
-
-* As mentioned in the 8.6 upgrade notes, a default autoscaling policy was provided starting in 8.6.0.
-This default autoscaling policy resulted in increasingly slow collection creation calls in large clusters (50+ collections).
-+
-In 8.6.1 the default autoscaling policy has been removed, and clusters will not use autoscaling unless a policy has explicitly been created.
-If your cluster is running 8.6.0 and *not using an explicit autoscaling policy*, upgrade to 8.6.1 and remove the default cluster policy and preferences via the following command.
-+
-Replace `localhost:8983` with your Solr endpoint.
-+
-[source,text]
-curl -X POST -H 'Content-type:application/json'  -d '{set-cluster-policy : [], set-cluster-preferences : []}' http://localhost:8983/api/cluster/autoscaling
-+
-This information is only relevant for users upgrading from 8.6.0.
-If upgrading from an earlier version to 8.6.1+, this warning can be ignored.
-
-=== Solr 8.6
-
-See the https://cwiki.apache.org/confluence/display/SOLR/ReleaseNote86[8.6 Release Notes^]
-for an overview of the main new features of Solr 8.6.
-
-When upgrading to 8.6.x users should be aware of the following major changes from 8.5.
-
-*Support for Block-Max WAND*
-
-Lucene added support for Block-Max WAND in 8.0, and 8.6 makes this available for Solr also.
-
-This can provide significant performance enhancements by not calculating the score for results which are not likely to appear in the top set of results.
-
-It is enabled when using a new query parameter `minExactCount`.
-This parameter tells Solr to accurately count the number of hits accurately until at least this value.
-Once this value is reached, Solr can skip over documents that don't have a score high enough to be in the top set of documents, which has the potential for greatly speeding up searches.
-
-It's important to note that when using this parameter, the hit count of searches may not be accurate.
-It is guaranteed that the hit count is accurate up to the value of `minExactCount`, but any returned hit count higher than that may be an approximation.
-
-A new boolean attribute `numFoundExact` is included in all responses to indicate if the hit count in the response is expected to be exact or not.
-
-More information about this new feature is available in the section xref:query-guide:common-query-parameters.adoc#minexactcount-parameter[minExactCount Parameter].
-
-*Autoscaling*
-
-* **NOTE: The default autoscaling policy has been removed as of 8.6.1**
-+
-Solr now includes a default autoscaling policy.
-This policy can be overridden with your custom rules or by specifying an empty policy to replace the default.
-
-* The ComputePlan action now supports a collection selector to identify collections based on collection properties to determine which collections should be operated on.
-
-*Security*
-
-* Prior to Solr 8.6 Solr APIs which take a file system location, such as core creation, backup, restore, and others, did not validate the path and Solr would allow any absolute or relative path.
-Starting in 8.6 only paths that are relative to `SOLR_HOME`, `SOLR_DATA_HOME` and `coreRootDir` are allowed by default.
-+
-If you need to create a core or store a backup outside the default paths, you will need to tell Solr which paths to allow.
-A new element in `solr.xml` called `allowPaths` takes a comma-separated list of allowed paths.
-+
-When using the `solr.xml` file that ships with 8.6, you can configure the list of paths to allow through the system property `solr.allowPaths`.
-Please see `bin/solr.in.sh` or `bin\solr.in.cmd` for example usage.
-Using the value `*` will allow any path as in earlier versions.
-+
-For more on this, see the section xref:configuration-guide:configuring-solr-xml.adoc#the-solr-element[Solr.xml Parameters].
-+
-Windows SMB shares on the UNC format, such as `\\myhost\myshare\mypath` are now always disallowed.
-Please use drive letter mounts instead, i.e., `S:\mypath`.
-
-* A new authorization plugin `ExternalRoleRuleBasedAuthorizationPlugin` is now available.
-This plugin allows an authentication plugin (such as JWT) to supply a user's roles instead of maintaining a user-to-role mapping inside Solr.
-
-* When authentication is enabled, the Admin UI Dashboard (main screen) now includes a panel that shows the authentication and authorization plugins in use, the logged in username, and the roles assigned to this user.
-A new link will also appear in the left-hand navigation to allow a user to log out.
-
-*Streaming Expressions*
-
-* The `/export` handler now supports streaming expressions to allow limiting the output of the export to only matching documents.
-+
-For more information about how to use this, see the section xref:query-guide:exporting-result-sets.adoc#specifying-the-local-streaming-expression[Specifying the Local Streaming Expression].
-
-* The `stats`, `facet`, and `timeseries` expressions now support percentiles and standard deviation aggregations.
-
-*Highlighting*
-
-For the Unified Highlighter: The setting `hl.fragsizeIsMinimum` now defaults to `false` because `true` was found to be a significant performance regression when highlighting lots of text.
-This will yield longer highlights on average compared to Solr 8.5 but relatively unchanged compared to previous releases.
-Furthermore, if your application highlights lots of text, you may want to experiment with lowering `hl.fragAlignRatio` to trade ideal fragment alignment for better performance.
-
-*Deprecations*
-
-A primary focus of the community is improving Solr's stability and supportability.
-With the addition of the package manager system in 8.4, we now have the ability to move some features into plugins maintained by third-parties with the expertise to properly develop and support them.
-Our goal is to make running Solr easier and less prone to outages and other headaches.
-In this spirit, the following features have been deprecated and are slated to be removed in Solr 9.0.
-
-* Cross Data Center Replication (CDCR), in its current form, is deprecated and is scheduled to be removed in 9.0.
-This feature is unlikely to be replaced by an identical plugin.
-However, the community is working on figuring out a replacement feature for disaster recovery and failover.
-
-* The Data Import Handler (DIH) is deprecated and is scheduled to be removed in 9.0.
-Work to replace DIH with a community-supported plugin is underway and may be available soon.
-
-* Support to store indexes and backups in HDFS is deprecated and is scheduled to be removed in 9.0.
-A community-supported version of this may be available as a plugin in the future.
-For more details, please see https://issues.apache.org/jira/browse/SOLR-14021[SOLR-14021^].
-
-Users interested in maintaining a feature as a plugin are encouraged to join the https://solr.apache.org/community.html#mailing-lists-chat[developer mailing list^] to find out more about how to help.
-
-=== Solr 8.5
-
-See the https://cwiki.apache.org/confluence/display/SOLR/ReleaseNote85[8.5 Release Notes^]
-for an overview of the main new features of Solr 8.5.
-
-When upgrading to 8.5.x users should be aware of the following major changes from 8.4.
-
-__Note: an index incompatibility warning was retroactively added below to 8.4 for users choosing a non-default postings format (e.g., "FST50").__
-
-*Considerations for a SolrCloud Upgrade*
-
-Solr 8.5 introduces a change in the format used for the elements in the Overseer queues and maps (see https://issues.apache.org/jira/browse/SOLR-14095[SOLR-14095] for technical discussion of the change).
-This queue is used internally by the Overseer to reliably handle
-operations, to communicate operation results between the Overseer and the coordinator node, and by the REQUESTSTATUS API for displaying information about async Collection operations.
-
-This change won’t require you to change any client-side code you should see no differences on the client side.
-However, it does require some care when upgrading an existing SolrCloud cluster depending on your upgrade strategy.
-
-If you are upgrading Solr with an atomic restart strategy:
-
-* If you don’t use async or REQUESTSTATUS operations, you should be able to restart and not see any issues.
-* If you do use Collection API operations:
-. Pause Collection API operations.
-. Cleanup queues (See the section xref:configuration-guide:collections-api.adoc#deletestatus[DELETESTATUS] for examples)
-if you use async operations.
-. Upgrade and restart the nodes.
-. Resume all normal operations.
-
-If you are upgrading Solr with a rolling restart strategy:
-
-* If you don’t use Collection API operations, you should be able to do a rolling restart and not see
-any issues.
-* If you do use Collection API operations, but you can pause their use during the restart the easiest
-way is to:
-. Pause Collection API operations.
-. Upgrade and restart all nodes.
-. Cleanup queues (See the section xref:configuration-guide:collections-api.adoc#deletestatus[DELETESTATUS] for examples)
-if you use async operations.
-. Resume all normal operations.
-
-If you use Collection API operations and can’t pause them during the upgrade:
-
-. Start 8.5 nodes with the system property: `-Dsolr.useUnsafeOverseerResponse=deserialization`.
-Ensure the
-Overseer node is upgraded last.
-. Once all nodes are in 8.5 and once you don’t need to read old status anymore, restart again removing the
-system property.
-
-If you prefer to keep the old (but insecure) serialization strategy, you can start your nodes using the system
-property: `-Dsolr.useUnsafeOverseerResponse=true`.
-Keep in mind that this will be removed in future version of Solr.
-
-*Security Manager*
-
-Solr now has the ability to run with a Java security manager enabled.
-To enable this, set the property `SOLR_SECURITY_MANAGER_ENABLED=true` in `solr.in.sh` or `solr.in.cmd`.
-Note that if you are using HDFS to store indexes, you cannot enable the security manager.
-
-In Solr 9.0, this will be the default.
-
-// See SOLR-14147: See also the section xref:deployment-guide:securing-solr.adoc#enable-security-manager[Enable Security Manager].
-
-*Block/Allow Specific IPs*
-
-Solr has two new parameters to allow you to restrict access to Solr using IP addresses.
-Use `SOLR_IP_WHITELIST` to configure a whitelist, and `SOLR_IP_BLACKLIST` to configure a blacklist.
-These properties are defined in `solr.in.sh` or `solr.in.cmd`.
-
-See also the section xref:deployment-guide:securing-solr.adoc#ip-access-control[Enable IP Access Control].
-
-*BlockJoin Facet Deprecation*
-
-The BlockJoinFacetComponent is marked for deprecation and will be removed in 9.0.
-Users are encouraged to migrate to `uniqueBlock()` in JSON Facet API.
-More information about this is available in the section xref:query-guide:json-faceting-domain-changes.adoc#block-join-domain-changes[Block Join Domain Changes].
-
-*Caching with the Boolean Query Parser*
-
-By default, the xref:query-guide:other-parsers.adoc#boolean-query-parser[Boolean Query Parser] caches queries in Solr's filterCache.
-It's now possible to disable this with the local param `cache=false`.
-
-*Indexing Log Files*
-
-Solr now includes a command line tool, `bin/postlogs` which will index Solr's log files into a collection.
-This provides an easy way to use Solr or visualization tools (such as Zeppelin) to troubleshoot problems with the system.
-
-See the documentation for more details at xref:query-guide:logs.adoc[].
-
-*Highlighting*
-
-Solr's Unified Highlighter now has two parameters to help control passage sizing, `hl.fragAlignRatio` and `hl.fragsizeIsMinimum`.
-See the section xref:query-guide:highlighting.adoc#unified-highlighter[Unified Highlighter] for details about these new parameters.
-Regardless of the settings, the passages may be sized differently than before.
-_Warning: These default settings were found to be a significant performance regression for apps that highlight lots of text with the default sentence break iterator.
-See the 8.6 upgrade notes for advise you can apply in 8.5._
-
-*Shared Library System Parameter*
-
-Solr's `solr.xml` file has long had support for a `sharedLib` parameter, which allows you to define a common location for .jar files that may need to be in the path for all cores.
-
-This property can now be defined in `solr.in.sh` or `solr.in.cmd` as a system property (`-Dsolr.sharedLib=/path/to/lib`) added to `SOLR_OPTS` (see `solr.in.sh` or `solr.in.cmd` for details).
-
-=== Solr 8.4
-
-See the https://cwiki.apache.org/confluence/display/SOLR/ReleaseNote84[8.4 Release Notes^]
-for an overview of the main new features of Solr 8.4.
-
-When upgrading to 8.4.x users should be aware of the following major changes from 8.3.
-
-*Reminder:*  If you set the `postingsFormat` or `docValuesFormat` in the schema in order to use a non-default option, you risk preventing yourself from upgrading your Solr software at future versions, due to changed version of the Lucene library.
-Multiple non-default postings formats changed in 8.4, thus rendering the index data from a previous index.
-This includes "FST50" which was recommended by the Solr TaggerHandler for performance reasons.
-There is now improved documentation to navigate this trade-off choice.
-
-*Package Management System*
-
-Version 8.4 introduces a package management system to Solr.
-The goals of the
-system are to allow hot (live) deployment of plugins, provide packaging
-guidelines for plugins, and standardize Solr's approach by following familiar
-concepts used in other package management systems.
-
-The system is designed to eventually replace use of the `<lib ../>` directive,
-the Blob Store, and other methods of deploying plugins and custom components
-to Solr.
-
-The system is currently considered experimental, so use with caution.
-It must
-be enabled with a system parameter passed at start up before it can be used.
-For details, please see the section xref:configuration-guide:package-manager.adoc[].
-
-With this feature Solr's Blob Store functionality is now deprecated and will likely be removed in 9.0.
-
-*Security*
-
-The follow mix of changes were all made with the intention of making Solr more secure out of the box.
-
-* The `solrconfig.xml` file in Solr's `_default` configset has been trimmed of
- the following previously pre-configured items:
-+
-** All `<lib .../>` directives.
-This means that Solr Cell (aka Tika), Learning
-to Rank, Clustering (with Carrot2), language identification, and Velocity (for
-the `/browse` sample search interface) are no longer enabled out of the box.
-** The `/browse`, `/tvrh`, and `/update/extract` request handlers.
-** The Term Vector Component.
-** The XSLT and Velocity response writers.
-+
-All of these items can be added to your Solr implementation by manually editing
-`solrconfig.xml` to add them back in, or use the xref:configuration-guide:config-api.adoc[].
-+
-The `sample_techproducts_configs` and the examples found in `./example` are unchanged.
-
-* Configsets that have been uploaded with an unsecured Configset API (i.e., when authentication is not enabled) are considered "Untrusted Configsets".
-+
-In order to bolster Solr's out-of-the-box security, these untrusted configsets
-are no longer allowed to use the `<lib .../>` directive to implement modules
-or custom Jars.
-+
-When upgrading to 8.4, if you are using untrusted configsets that contain `<lib ../>`
-directives, their corresponding collections will not load (they will cease to
-work).
-You have a few options in this case:
-
-** You can secure your Solr instance with xref:deployment-guide:authentication-and-authorization-plugins.adoc[authentication] and re-upload the configset (using the `bin/solr zk upconfig ...` xref:deployment-guide:solr-control-script-reference.adoc[Solr CLI] command);
-** You can put your custom Jars in Solr's classpath instead of `lib` directories;
-** You can try the new package management system to manage your custom Jars.
-+
-See the section xref:configuration-guide:configsets-api.adoc#configsets-upload[Upload a Configset] for more details about trusted vs. untrusted configsets.
-
-* Our default Jetty configuration has been updated to now set a
-Content-Security-Policy (CSP) by default.
-See `./server/etc/jetty.xml` for
-details about how it is configured.
-+
-As a result of this change, any custom HTML served by Solr's HTTP server that contains inline Javascript will no longer execute in modern browsers.
-The options for you are:
-
-** Change your JavaScript code to not run inline any longer;
-** Edit `jetty.xml` to remove CSP (creating weaker security protection);
-** Remove/alter the headers with a reverse proxy.
-
-* Solr's Blob Store and runtime libs functionality are now deprecated and are planned to be removed from Solr in version 9.0.
-It has been replaced with the new package management system.
-
-* The Velocity response writer is also now deprecated and is planned to be removed from Solr in version 9.0.
-
-*Using Collapse with Group Disallowed*
-
-Using the xref:query-guide:collapse-and-expand-results.adoc[CollapsingQueryParser] with xref:query-guide:result-grouping.adoc[] has never been supported as it causes inconsistent behavior and NullPointerException errors.
-We have now explicitly disallowed this combination to prevent these errors.
-If you are using these together, you will need to modify your queries.
-
-*SolrJ*
-
-* SolrJ now supports the `shards.preference` parameter for single-shard
-scenarios to ensure multi-shard and single-shard request routing works in the same way.
-+
-See xref:deployment-guide:solrj.adoc#cloud-request-routing[Cloud Request Routing] and xref:deployment-guide:solrcloud-distributed-requests.adoc#shards-preference-parameter[shards.preference Parameter] for details.
-
-* `QueryResponse.getExplainMap()` type has changed from `Map<String, String>` to `Map<String, Object>` in order to support structured explanations.
-+
-This change is expected to be mostly back-compatible.
-Compiled third-party
-components will work the same due to type erasure, but source code changes may
-be required.
-
-* Replica routing code has been moved to SolrJ, making those classes available
-to clients if necessary.
-
-*Streaming Expressions*
-
-* A new DBSCAN clustering streaming evaluator has been added.
-
-* The `precision` stream evaluator can now operate on matrices.
-
-* The `random` streaming expression can now create the x-axis.
-
-*JSON Facets*
-
-* Two new aggregations have been added: `missing` and `countvals`.
-
-* Several aggregations now support multi-valued fields: `min`, `max`, `avg`, `sum`, `sumsq`, `stddev`, `variance`, and `percentile`.
-
-*Caches*
-
-* After the addition of `CaffeineCache` in 8.3, legacy SolrCache
-implementations are deprecated and likely to be removed in 9.0.
-+
-Users are encouraged to transition their cache configurations to use
-`org.apache.solr.search.CaffeineCache` as soon as feasible.
-
-=== Solr 8.3
-
-See the https://cwiki.apache.org/confluence/display/SOLR/ReleaseNote83[8.3 Release Notes^] for an overview of the main new features of Solr 8.3.
-
-When upgrading to 8.3.x users should be aware of the following major changes from 8.2.
-
-*JWT Authentication*
-
-JWT Authentication now supports multiple identity providers.
-To allow this, the parameter `jwkUrl` has been deprecated and replaced with `jwksUrl`.
-Implementations using `jwkUrl` will continue to work as normal, but users
- should plan to transition their configurations to use `jwksUrl` instead as
- soon as feasible.
-
-*Caches*
-
-* Solr has a new cache implementation, `CaffeineCache`, which is now recommended over other caches.
-This cache is expected to generally provide most users lower memory footprint, higher hit ratio, and better multi-threaded performance.
-+
-Since caching has a direct impact on the performance of your Solr
- implementation, before switching to any new cache implementation in
- production, take care to test for your environment and traffic patterns so
- you fully understand the ramifications of the change.
-
-* A new parameter, `maxIdleTime`, allows automatic eviction of cache items that have not been used in the defined amount of time.
-This allows the cache to release some memory and should aid those who want or need to fine-tune their caches.
-
-See the section xref:configuration-guide:caches-warming.adoc[] for more details about these and other cache options and parameters.
-
-=== Solr 8.2
-
-See the https://cwiki.apache.org/confluence/display/SOLR/ReleaseNote82[8.2 Release Notes^] for an overview of the main new features of Solr 8.2.
-
-When upgrading to 8.2.x, users should be aware of the following major changes from v8.1.
-
-*ZooKeeper 3.5.5*
-
-Solr 8.2 updates the version of ZooKeeper included with Solr to v3.5.5.
-
-It is recommended that external ensembles set up to work with Solr also be updated to ZooKeeper 3.5.5.
-
-This ZooKeeper release includes many new security features.
-In order for Solr's Admin UI to work with 3.5.5, the `zoo.cfg` file must allow access to ZooKeeper's "four-letter commands".
-At a minimum, `ruok`, `conf`, and `mntr` must be enabled, but other commands can optionally be enabled if you choose.
-See the section xref:deployment-guide:zookeeper-ensemble.adoc#configuration-for-a-zookeeper-ensemble[Configuration for a ZooKeeper Ensemble] for details.
-
-[WARNING]
-Until 8.3, https://issues.apache.org/jira/browse/SOLR-13672[SOLR-13672] causes the ZK Status screen in the Admin UI to not be able to report status.
-This only impacts the UI, ZooKeeper still operates correctly.
-
-*Routed Aliases*
-
-* Routed aliases now use collection properties to identify collections that belong to the alias; prior to 8.2, these aliases used core properties.
-+
-This is backward-compatible and aliases created with prior versions will
- continue to work.
-However, new collections will no longer add the
- `routedAliasName` property to the `core.properties` file so any external code
- depending on this location will need to be updated.
-
-// TODO: aliases.adoc still says this is per-core?
-
-* Time-routed aliases now include a `TRA` infix in the collection name, in the pattern `<alias>_TRA_<timestamp>`. +
-Collections created with older versions will continue to work.
-
-*Distributed Tracing Support*
-
-This release adds support for tracing requests in Solr.
-Please review the section xref:deployment-guide:distributed-tracing.adoc[] for details on how to configure this feature.
-
-=== Solr 8.1
-
-See the https://cwiki.apache.org/confluence/display/SOLR/ReleaseNote810[8.1 Release Notes^] for an overview of the main new features of Solr 8.1.
-
-When upgrading to 8.1.x, users should be aware of the following major changes from v8.0.
-
-*Global maxBooleanClauses Parameter*
-
-* The behavior of the `maxBooleanClauses` parameter has changed to reduce the risk of exponential query expansion when dealing with pathological query strings.
-+
-A default upper limit of 1024 clauses is now enforced at the node level.
-This was the default prior to 7.0, and it can be overridden with a new global parameter in `solr.xml`.
-This limit will be enforced for all queries whether explicitly defined by the user (or client), or created by Solr and Lucene internals.
-+
-An identical parameter is available in `solrconfig.xml` for limiting the size of queries explicitly defined by the user (or client), but this per-collection limit will still be restricted by the global limit set in `solr.xml`.
-+
-If your use case demands that you a lot of OR or AND clauses in your queries, upon upgrade to 8.1 you may need to adjust the global `maxBooleanClauses` parameter since between 7.0 and 8.1 the limit was effectively unbounded.
-+
-For more information about the new parameter, see the section xref:configuration-guide:configuring-solr-xml.adoc#global-maxbooleanclauses[maxBooleanClauses].
-
-*Security*
-
-* JSON Web Tokens (JWT) are now supported for authentication.
-These allow Solr to assert a user is already authenticated via an external identity provider, such as an OpenID Connect-enabled IdP.
-For more information, see the section xref:deployment-guide:jwt-authentication-plugin.adoc[].
-
-* A new security plugin for audit logging has been added.
-A default class `SolrLogAuditLoggerPlugin` is available and configurable in `security.json`.
-The base class is also extendable for adding custom audit plugins if needed.
-See the section xref:deployment-guide:audit-logging.adoc[] for more information.
-
-*Collections API*
-
-* The output of the REQUESTSTATUS command in the Collections API will now include internal asynchronous requests (if any) in the "success" or "failed" keys.
-
-* The CREATE command will now return the appropriate status code (4xx, 5xx, etc.) when the command has failed.
-Previously, it always returned `0`, even in failure.
-
-* The MODIFYCOLLECTION command now accepts an attribute to set a collection as read-only.
-This can be used to block a collection from receiving any updates while still allowing queries to be served.
-See the section xref:deployment-guide:collection-management.adoc#modifycollection[MODIFYCOLLECTION] for details on how to use it.
-
-* A new command RENAME allows renaming a collection by setting up a one-to-one alias using the new name.
-For more information, see the section xref:deployment-guide:collection-management.adoc#rename[RENAME].
-
-* A new command REINDEXCOLLECTION allows indexing existing stored fields from a source collection into a new collection.
-For more information, please see the section xref:deployment-guide:collection-management.adoc#reindexcollection[REINDEXCOLLECTION].
-
-*Logging*
-
-* The default Log4j2 logging mode has been changed from synchronous to asynchronous.
-This will improve logging throughput and reduce system contention at the cost of a _slight_ chance that some logging messages may be missed in the event of abnormal Solr termination.
-+
-If even this slight risk is unacceptable, the Log4j configuration file found in `server/resources/log4j2.xml` has the synchronous logging configuration in a commented section and can be edited to re-enable synchronous logging.
-
-*Metrics*
-
-* The SolrGangliaReporter has been removed from Solr.
-The metrics library used by Solr, Dropwizard Metrics, was updated to version 4, and Ganglia support was removed from it due to a dependency on the LGPL license.
-
-*Browse UI (Velocity)*
-
-* Velocity and Velocity Tools were both upgraded as part of this release.
-Velocity upgraded from 1.7 to 2.0.
-Please see https://velocity.apache.org/engine/2.0/upgrading.html about upgrading.
-Velocity Tools upgraded from 2.0 to 3.0.
-For more details, please see https://velocity.apache.org/tools/3.0/upgrading.html for details about the upgrade.
-
-*Default Garbage Collector (GC)*
-
-* Solr's default GC has been changed from CMS to G1.
-If you prefer to use CMS or any other GC method, you can modify the `GC_TUNE` section of `solr.in.sh` (*nix) or `solr.in.cmd` (Windows).
-
-
-== Upgrading from 7.x Releases
-
-The upgrade from 7.x to Solr 8.0 introduces several major changes that you should be aware of before upgrading.
-These changes are described in the section xref:major-changes-in-solr-8.adoc[].
+The upgrade from 8.x to Solr 9.0 introduces several *major* changes that you should be aware of before upgrading.
+These changes are described in the section xref:major-changes-in-solr-9.adoc[].
 It's strongly recommended that you do a thorough review of that section before starting your upgrade.
 
 [NOTE]
-If you run in SolrCloud mode, you must be on Solr version 7.3 or higher in order to upgrade to 8.x.
+If you run in SolrCloud mode and use SolrJ's `CloudSolrClient`, you must first upgrade SolrJ to version 8.10 or higher before upgrading the cluster to 9.0.
+
+[NOTE]
+Rolling upgrades from Solr 8 to Solr 9 require first upgrading the cluster to version 8.7 or newer.
 
-== Upgrading from Pre-7.x Versions
+== Upgrading from Pre-8.x Versions
 
-Users upgrading from versions of Solr prior to 7.x are strongly encouraged to consult {solr-javadocs}/changes/Changes.html[`CHANGES.txt`] for the details of _all_ changes since the version they are upgrading from.
+Users upgrading from versions of Solr prior to 8.x are strongly encouraged to consult {solr-javadocs}/changes/Changes.html[`CHANGES.txt`] for the details of _all_ changes since the version they are upgrading from.
 
-The upgrade from Solr 6.x to Solr 7.0 introduced several *major* changes that you should be aware of before upgrading.
-Please do a thorough review of the section xref:major-changes-in-solr-7.adoc[] before starting your upgrade.
+The upgrade from Solr 7.x to Solr 8.0 introduced several *major* changes that you should be aware of before upgrading.
+Please do a thorough review of the section xref:major-changes-in-solr-8.adoc[] before starting your upgrade.
 
-A summary of the significant changes between Solr 5.x and Solr 6.0 is in the section xref:major-changes-in-solr-6.adoc[].
+A summary of the significant changes between Solr 6.x and Solr 7.0 is in the section xref:major-changes-in-solr-7.adoc[].