[jira] [Commented] (SOLR-9648) Wrap all solr merge policies with SolrMergePolicy

["Christine Poerschke (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SOLR-9648?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15598472#comment-15598472 ] 

Christine Poerschke commented on SOLR-9648:
-------------------------------------------

I like the idea of using segment merging and a merge policy to upgrade segments.

Wrapping the solrconfig.xml configured merge policy in a {{SolrMergePolicy}} and thus changing the 'what you configure is what you get' approach, hmm, not so sure about that though because
* currently force-merge happens only when externally triggered
* the force-merge behaviour added by the wrap is (proposed to be) executed only on startup
* the configured merge policy could (at least theoretically) disallow force merges

POC WIP patch notes:
* The {{MAX_UPGRADES_AT_A_TIME = 5;}} sounds similar to what the [MergeScheduler|http://lucene.apache.org/core/6_2_1/core/org/apache/lucene/index/MergeScheduler.html] does (unless merge-on-startup bypasses the merge scheduler somehow?)
* IndexWriter has a {{UNBOUNDED_MAX_MERGE_SEGMENTS==-1}} which if made non-private could perhaps be used in the {{cmd.maxOptimizeSegments = Integer.MAX_VALUE;}}
* The SolrMergePolicy has no solr dependencies, might it be renamed to something else and be part of the lucene code base? [UpgradeIndexMergePolicy|http://lucene.apache.org/core/6_2_1/core/org/apache/lucene/index/UpgradeIndexMergePolicy.html] also sounds very similar actually.

> Wrap all solr merge policies with SolrMergePolicy
> -------------------------------------------------
>
>                 Key: SOLR-9648
>                 URL: https://issues.apache.org/jira/browse/SOLR-9648
>             Project: Solr
>          Issue Type: Bug
>      Security Level: Public(Default Security Level. Issues are Public) 
>            Reporter: Keith Laban
>         Attachments: SOLR-9648-WIP.patch
>
>
> Wrap the entry point for all merge policies with a single entry point merge policy for more fine grained control over merging with minimal configuration. 
> The main benefit will be to allow upgrading of segments on startup when lucene version changes. Ideally we can use the same approach for adding and removing of doc values when the schema changes and hopefully other index type changes such as Trie -> Point types, or even analyzer changes. 



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