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Posted to commits@flink.apache.org by tz...@apache.org on 2019/08/22 05:32:33 UTC
[flink] branch master updated: [FLINK-13712] [docs] Add release
notes for Flink 1.9.0
This is an automated email from the ASF dual-hosted git repository.
tzulitai pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/flink.git
The following commit(s) were added to refs/heads/master by this push:
new 607e5d1 [FLINK-13712] [docs] Add release notes for Flink 1.9.0
607e5d1 is described below
commit 607e5d1656f431af7633323052a2460cabe9d508
Author: Tzu-Li (Gordon) Tai <tz...@apache.org>
AuthorDate: Wed Aug 14 17:01:26 2019 +0200
[FLINK-13712] [docs] Add release notes for Flink 1.9.0
---
docs/index.md | 1 +
docs/index.zh.md | 1 +
docs/release-notes/flink-1.9.md | 239 +++++++++++++++++++++++++++++++++++++
docs/release-notes/flink-1.9.zh.md | 239 +++++++++++++++++++++++++++++++++++++
4 files changed, 480 insertions(+)
diff --git a/docs/index.md b/docs/index.md
index b0a74de..9d35c3f 100644
--- a/docs/index.md
+++ b/docs/index.md
@@ -47,6 +47,7 @@ Before putting your Flink job into production, read the [Production Readiness Ch
Release notes cover important changes between Flink versions. Please carefully read these notes if you plan to upgrade your Flink setup to a later version.
+* [Release notes for Flink 1.9](release-notes/flink-1.9.html).
* [Release notes for Flink 1.8](release-notes/flink-1.8.html).
* [Release notes for Flink 1.7](release-notes/flink-1.7.html).
* [Release notes for Flink 1.6](release-notes/flink-1.6.html).
diff --git a/docs/index.zh.md b/docs/index.zh.md
index 5fccc1f..898a2a2 100644
--- a/docs/index.zh.md
+++ b/docs/index.zh.md
@@ -44,6 +44,7 @@ Apache Flink 是一个分布式流批一体化的开源平台。Flink 的核心
发布日志包含了 Flink 版本之间的重大更新。请在你升级 Flink 之前仔细阅读相应的发布日志。
+* [Flink 1.9 的发布日志](release-notes/flink-1.9.html)。
* [Flink 1.8 的发布日志](release-notes/flink-1.8.html)。
* [Flink 1.7 的发布日志](release-notes/flink-1.7.html)。
* [Flink 1.6 的发布日志](release-notes/flink-1.6.html)。
diff --git a/docs/release-notes/flink-1.9.md b/docs/release-notes/flink-1.9.md
new file mode 100644
index 0000000..dedfa4c
--- /dev/null
+++ b/docs/release-notes/flink-1.9.md
@@ -0,0 +1,239 @@
+---
+title: "Release Notes - Flink 1.9"
+---
+<!--
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements. See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership. The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License. You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied. See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+
+
+These release notes discuss important aspects, such as configuration, behavior,
+or dependencies, that changed between Flink 1.8 and Flink 1.9. It also provides an overview
+on known shortcoming or limitations with new experimental features introduced in 1.9.
+
+Please read these notes carefully if you are planning to upgrade your Flink version to 1.9.
+
+* This will be replaced by the TOC
+{:toc}
+
+## Known shortcomings or limitations for new features
+
+### New Table / SQL Blink planner
+
+Flink 1.9.0 provides support for two planners for the Table API, namely Flink's original planner and the new Blink
+planner. The original planner maintains same behaviour as previous releases, while the new Blink planner is still
+considered experimental and has the following limitations:
+
+- The Blink planner can not be used with `BatchTableEnvironment`, and therefore Table programs ran with the planner can not
+be transformed to `DataSet` programs. This is by design and will also not be supported in the future. Therefore, if
+you want to run a batch job with the Blink planner, please use the new `TableEnvironment`. For streaming jobs,
+both `StreamTableEnvironment` and `TableEnvironment` works.
+- Implementations of `StreamTableSink` should implement the `consumeDataStream` method instead of `emitDataStream`
+if it is used with the Blink planner. Both methods work with the original planner.
+This is by design to make the returned `DataStreamSink` accessible for the planner.
+- Due to a bug with how transformations are not being cleared on execution, `TableEnvironment` instances should not
+be reused across multiple SQL statements when using the Blink planner.
+- `Table.flatAggregate` is not supported
+- Session and count windows are not supported when running batch jobs.
+- The Blink planner only supports the new `Catalog` API, and does not support `ExternalCatalog` which is now deprecated.
+
+Related issues:
+- [FLINK-13708: Transformations should be cleared because a table environment could execute multiple job](https://issues.apache.org/jira/browse/FLINK-13708)
+- [FLINK-13473: Add GroupWindowed FlatAggregate support to stream Table API (Blink planner), i.e, align with Flink planner](https://issues.apache.org/jira/browse/FLINK-13473)
+- [FLINK-13735: Support session window with Blink planner in batch mode](https://issues.apache.org/jira/browse/FLINK-13735)
+- [FLINK-13736: Support count window with Blink planner in batch mode](https://issues.apache.org/jira/browse/FLINK-13736)
+
+### SQL DDL
+
+In Flink 1.9.0, the community also added a preview feature about SQL DDL, but only for batch style DDLs.
+Therefore, all streaming related concepts are not supported yet, for example watermarks.
+
+Related issues:
+- [FLINK-13661: Add a stream specific CREATE TABLE SQL DDL](https://issues.apache.org/jira/browse/FLINK-13661)
+- [FLINK-13568: DDL create table doesn't allow STRING data type](https://issues.apache.org/jira/browse/FLINK-13568)
+
+### Java 9 support
+
+Since Flink 1.9.0, Flink can now be compiled and run on Java 9. Note that certain components interacting
+with external systems (connectors, filesystems, metric reporters, etc.) may not work since the respective projects may
+have skipped Java 9 support.
+
+Related issues:
+- [FLINK-8033: JDK 9 support](https://issues.apache.org/jira/browse/FLINK-8033)
+
+## Deprecations and breaking changes
+
+### Scala expression DSL for Table API moved to `flink-table-api-scala`
+
+Since 1.9.0, the implicit conversions for the Scala expression DSL for the Table API has been moved to
+`flink-table-api-scala`. This requires users to update the imports in their Table programs.
+
+Users of pure Table programs should define their imports like:
+
+```
+import org.apache.flink.table.api._
+
+TableEnvironment.create(...)
+```
+
+Users of the DataStream API should define their imports like:
+
+```
+import org.apache.flink.table.api._
+import org.apache.flink.table.api.scala._
+
+StreamTableEnvironment.create(...)
+```
+
+Related issues:
+- [FLINK-13045: Move Scala expression DSL to flink-table-api-scala](https://issues.apache.org/jira/browse/FLINK-13045)
+
+### Failover strategies
+
+As a result of completing fine-grained recovery ([FLIP-1](https://cwiki.apache.org/confluence/display/FLINK/FLIP-1+%3A+Fine+Grained+Recovery+from+Task+Failures)),
+Flink will now attempt to only restart tasks that are
+connected to failed tasks through a pipelined connection. By default, the `region` failover strategy is used.
+
+Users who were not using a restart strategy or have already configured a failover strategy should not be affected.
+Moreover, users who already enabled the `region` failover strategy, along with a restart strategy that enforces a
+certain number of restarts or introduces a restart delay, will see changes in behavior.
+The `region` failover strategy now correctly respects constraints that are defined by the restart strategy.
+
+Streaming users who were not using a failover strategy may be affected if their jobs are embarrassingly parallel or
+contain multiple independent jobs. In this case, only the failed parallel pipeline or affected jobs will be restarted.
+
+Batch users may be affected if their job contains blocking exchanges (usually happens for shuffles) or the
+`ExecutionMode` was set to `BATCH` or `BATCH_FORCED` via the `ExecutionConfig`.
+
+Overall, users should see an improvement in performance.
+
+Related issues:
+- [FLINK-13223: Set jobmanager.execution.failover-strategy to region in default flink-conf.yaml](https://issues.apache.org/jira/browse/FLINK-13223)
+- [FLINK-13060: FailoverStrategies should respect restart constraints](https://issues.apache.org/jira/browse/FLINK-13060)
+
+### Job termination via CLI
+
+With the support of graceful job termination with savepoints for semantic correctness
+([FLIP-34](https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=103090212)), a few changes
+related to job termination has been made to the CLI.
+
+From now on, the `stop` command with no further arguments stops the job with a savepoint targeted at the
+default savepoint location (as configured via the `state.savepoints.dir` property in the job configuration),
+or a location explicitly specified using the `-p <savepoint-path>` option. Please make sure to configure the
+savepoint path using either one of these options.
+
+Since job terminations are now always accompanied with a savepoint, stopping jobs is expected to take longer now.
+
+Related issues:
+- [FLINK-13123: Align Stop/Cancel Commands in CLI and REST Interface and Improve Documentation](https://issues.apache.org/jira/browse/FLINK-13123)
+- [FLINK-11458: Add TERMINATE/SUSPEND Job with Savepoint](https://issues.apache.org/jira/browse/FLINK-11458)
+
+### Network stack
+
+A few changes in the network stack related to changes in the threading model of `StreamTask` to a mailbox-based approach
+requires close attention to some related configuration:
+
+- Due to changes in the lifecycle management of result partitions, partition requests as well as re-triggers will now
+happen sooner. Therefore, it is possible that some jobs with long deployment times and large state might start failing
+more frequently with `PartitionNotFound` exceptions compared to previous versions. If that's the case, users should
+increase the value of `taskmanager.network.request-backoff.max` in order to have the same effective partition
+request timeout as it was prior to 1.9.0.
+
+- To avoid a potential deadlock, a timeout has been added for how long a task will wait for assignment of exclusive
+memory segments. The default timeout is 30 seconds, and is configurable via `taskmanager.network.memory.exclusive-buffers-request-timeout-ms`.
+It is possible that for some previously working deployments this default timeout value is too low
+and might have to be increased.
+
+Please also notice that several network I/O metrics have had their scope changed. See the [1.9 metrics documentation](https://ci.apache.org/projects/flink/flink-docs-master/monitoring/metrics.html)
+for which metrics are affected. In 1.9.0, these metrics will still be available under their previous scopes, but this
+may no longer be the case in future versions.
+
+Related issues:
+- [FLINK-13013: Make sure that SingleInputGate can always request partitions](https://issues.apache.org/jira/browse/FLINK-13013)
+- [FLINK-12852: Deadlock occurs when requiring exclusive buffer for RemoteInputChannel](https://issues.apache.org/jira/browse/FLINK-12852)
+- [FLINK-12555: Introduce an encapsulated metric group layout for shuffle API and deprecate old one](https://issues.apache.org/jira/browse/FLINK-12555)
+
+### AsyncIO
+
+Due to a bug in the `AsyncWaitOperator`, in 1.9.0 the default chaining behaviour of the operator is now changed so
+that it is never chained after another operator. This should not be problematic for migrating from older version
+snapshots as long as an uid was assigned to the operator. If an uid was not assigned to the operator, please see
+the instructions [here](https://ci.apache.org/projects/flink/flink-docs-release-1.9/ops/upgrading.html#matching-operator-state)
+for a possible workaround.
+
+Related issues:
+- [FLINK-13063: AsyncWaitOperator shouldn't be releasing checkpointingLock](https://issues.apache.org/jira/browse/FLINK-13063)
+
+### Connectors and Libraries
+
+#### Introduced `KafkaSerializationSchema` to fully replace `KeyedSerializationSchema`
+
+The universal `FlinkKafkaProducer` (in `flink-connector-kafka`) supports a new `KafkaSerializationSchema` that will
+fully replace `KeyedSerializationSchema` in the long run. This new schema allows directly generating Kafka
+`ProducerRecord`s for sending to Kafka, therefore enabling the user to use all available Kafka features (in the context
+of Kafka records).
+
+#### Dropped connectors and libraries
+
+- The Elasticsearch 1 connector has been dropped and will no longer receive patches. Users may continue to use the
+connector from a previous series (like 1.8) with newer versions of Flink. It is being dropped due to being used
+significantly less than more recent versions (Elasticsearch versions 2.x and 5.x are downloaded 4 to 5 times more), and
+hasn't seen any development for over a year.
+
+- The older Python APIs for batch and streaming have been removed and will no longer receive new patches.
+A new API is being developed based on the Table API as part of [FLINK-12308: Support python language in Flink Table API](https://issues.apache.org/jira/browse/FLINK-12308).
+Existing users may continue to use these older APIs with future versions of Flink by copying both the `flink-streaming-python`
+and `flink-python` jars into the `/lib` directory of the distribution and the corresponding start scripts `pyflink-stream.sh`
+and `pyflink.sh` into the `/bin` directory of the distribution.
+
+- The older machine learning libraries have been removed and will no longer receive new patches.
+This is due to efforts towards a new Table-based machine learning library ([FLIP-39](https://docs.google.com/document/d/1StObo1DLp8iiy0rbukx8kwAJb0BwDZrQrMWub3DzsEo/edit)).
+Users can still use the 1.8 version of the legacy library if their projects still rely on it.
+
+Related issues:
+- [FLINK-11693: Add KafkaSerializationSchema that directly uses ProducerRecord](https://issues.apache.org/jira/browse/FLINK-11693)
+- [FLINK-12151: Drop Elasticsearch 1 connector](https://issues.apache.org/jira/browse/FLINK-12151)
+- [FLINK-12903: Remove legacy flink-python APIs](https://issues.apache.org/jira/browse/FLINK-12903)
+- [FLINK-12308: Support python language in Flink Table API](https://issues.apache.org/jira/browse/FLINK-12308)
+- [FLINK-12597: Remove the legacy flink-libraries/flink-ml](https://issues.apache.org/jira/browse/FLINK-12597)
+
+### MapR dependency removed
+
+Dependency on MapR vendor-specific artifacts has been removed, by changing the MapR filesystem connector to work
+purely based on reflection. This does not introduce any regession in the support for the MapR filesystem.
+The decision to remove hard dependencies on the MapR artifacts was made due to very flaky access to the secure https
+endpoint of the MapR artifact repository, and affected build stability of Flink.
+
+Related issues:
+- [FLINK-12578: Use secure URLs for Maven repositories](https://issues.apache.org/jira/browse/FLINK-12578)
+- [FLINK-13499: Remove dependency on MapR artifact repository](https://issues.apache.org/jira/browse/FLINK-13499)
+
+### StateDescriptor interface change
+
+Access to the state serializer in `StateDescriptor` is now modified from protected to private access. Subclasses
+should use the `StateDescriptor#getSerializer()` method as the only means to obtain the wrapped state serializer.
+
+Related issues:
+- [FLINK-12688: Make serializer lazy initialization thread safe in StateDescriptor](https://issues.apache.org/jira/browse/FLINK-12688)
+
+### Web UI dashboard
+
+The web frontend of Flink has been updated to use the latest Angular version (7.x). The old frontend remains
+available in Flink 1.9.x, but will be removed in a later Flink release once the new frontend is considered stable.
+
+Related issues:
+- [FLINK-10705: Rework Flink Web Dashoard](https://issues.apache.org/jira/browse/FLINK-10705)
diff --git a/docs/release-notes/flink-1.9.zh.md b/docs/release-notes/flink-1.9.zh.md
new file mode 100644
index 0000000..dedfa4c
--- /dev/null
+++ b/docs/release-notes/flink-1.9.zh.md
@@ -0,0 +1,239 @@
+---
+title: "Release Notes - Flink 1.9"
+---
+<!--
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements. See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership. The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License. You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied. See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+
+
+These release notes discuss important aspects, such as configuration, behavior,
+or dependencies, that changed between Flink 1.8 and Flink 1.9. It also provides an overview
+on known shortcoming or limitations with new experimental features introduced in 1.9.
+
+Please read these notes carefully if you are planning to upgrade your Flink version to 1.9.
+
+* This will be replaced by the TOC
+{:toc}
+
+## Known shortcomings or limitations for new features
+
+### New Table / SQL Blink planner
+
+Flink 1.9.0 provides support for two planners for the Table API, namely Flink's original planner and the new Blink
+planner. The original planner maintains same behaviour as previous releases, while the new Blink planner is still
+considered experimental and has the following limitations:
+
+- The Blink planner can not be used with `BatchTableEnvironment`, and therefore Table programs ran with the planner can not
+be transformed to `DataSet` programs. This is by design and will also not be supported in the future. Therefore, if
+you want to run a batch job with the Blink planner, please use the new `TableEnvironment`. For streaming jobs,
+both `StreamTableEnvironment` and `TableEnvironment` works.
+- Implementations of `StreamTableSink` should implement the `consumeDataStream` method instead of `emitDataStream`
+if it is used with the Blink planner. Both methods work with the original planner.
+This is by design to make the returned `DataStreamSink` accessible for the planner.
+- Due to a bug with how transformations are not being cleared on execution, `TableEnvironment` instances should not
+be reused across multiple SQL statements when using the Blink planner.
+- `Table.flatAggregate` is not supported
+- Session and count windows are not supported when running batch jobs.
+- The Blink planner only supports the new `Catalog` API, and does not support `ExternalCatalog` which is now deprecated.
+
+Related issues:
+- [FLINK-13708: Transformations should be cleared because a table environment could execute multiple job](https://issues.apache.org/jira/browse/FLINK-13708)
+- [FLINK-13473: Add GroupWindowed FlatAggregate support to stream Table API (Blink planner), i.e, align with Flink planner](https://issues.apache.org/jira/browse/FLINK-13473)
+- [FLINK-13735: Support session window with Blink planner in batch mode](https://issues.apache.org/jira/browse/FLINK-13735)
+- [FLINK-13736: Support count window with Blink planner in batch mode](https://issues.apache.org/jira/browse/FLINK-13736)
+
+### SQL DDL
+
+In Flink 1.9.0, the community also added a preview feature about SQL DDL, but only for batch style DDLs.
+Therefore, all streaming related concepts are not supported yet, for example watermarks.
+
+Related issues:
+- [FLINK-13661: Add a stream specific CREATE TABLE SQL DDL](https://issues.apache.org/jira/browse/FLINK-13661)
+- [FLINK-13568: DDL create table doesn't allow STRING data type](https://issues.apache.org/jira/browse/FLINK-13568)
+
+### Java 9 support
+
+Since Flink 1.9.0, Flink can now be compiled and run on Java 9. Note that certain components interacting
+with external systems (connectors, filesystems, metric reporters, etc.) may not work since the respective projects may
+have skipped Java 9 support.
+
+Related issues:
+- [FLINK-8033: JDK 9 support](https://issues.apache.org/jira/browse/FLINK-8033)
+
+## Deprecations and breaking changes
+
+### Scala expression DSL for Table API moved to `flink-table-api-scala`
+
+Since 1.9.0, the implicit conversions for the Scala expression DSL for the Table API has been moved to
+`flink-table-api-scala`. This requires users to update the imports in their Table programs.
+
+Users of pure Table programs should define their imports like:
+
+```
+import org.apache.flink.table.api._
+
+TableEnvironment.create(...)
+```
+
+Users of the DataStream API should define their imports like:
+
+```
+import org.apache.flink.table.api._
+import org.apache.flink.table.api.scala._
+
+StreamTableEnvironment.create(...)
+```
+
+Related issues:
+- [FLINK-13045: Move Scala expression DSL to flink-table-api-scala](https://issues.apache.org/jira/browse/FLINK-13045)
+
+### Failover strategies
+
+As a result of completing fine-grained recovery ([FLIP-1](https://cwiki.apache.org/confluence/display/FLINK/FLIP-1+%3A+Fine+Grained+Recovery+from+Task+Failures)),
+Flink will now attempt to only restart tasks that are
+connected to failed tasks through a pipelined connection. By default, the `region` failover strategy is used.
+
+Users who were not using a restart strategy or have already configured a failover strategy should not be affected.
+Moreover, users who already enabled the `region` failover strategy, along with a restart strategy that enforces a
+certain number of restarts or introduces a restart delay, will see changes in behavior.
+The `region` failover strategy now correctly respects constraints that are defined by the restart strategy.
+
+Streaming users who were not using a failover strategy may be affected if their jobs are embarrassingly parallel or
+contain multiple independent jobs. In this case, only the failed parallel pipeline or affected jobs will be restarted.
+
+Batch users may be affected if their job contains blocking exchanges (usually happens for shuffles) or the
+`ExecutionMode` was set to `BATCH` or `BATCH_FORCED` via the `ExecutionConfig`.
+
+Overall, users should see an improvement in performance.
+
+Related issues:
+- [FLINK-13223: Set jobmanager.execution.failover-strategy to region in default flink-conf.yaml](https://issues.apache.org/jira/browse/FLINK-13223)
+- [FLINK-13060: FailoverStrategies should respect restart constraints](https://issues.apache.org/jira/browse/FLINK-13060)
+
+### Job termination via CLI
+
+With the support of graceful job termination with savepoints for semantic correctness
+([FLIP-34](https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=103090212)), a few changes
+related to job termination has been made to the CLI.
+
+From now on, the `stop` command with no further arguments stops the job with a savepoint targeted at the
+default savepoint location (as configured via the `state.savepoints.dir` property in the job configuration),
+or a location explicitly specified using the `-p <savepoint-path>` option. Please make sure to configure the
+savepoint path using either one of these options.
+
+Since job terminations are now always accompanied with a savepoint, stopping jobs is expected to take longer now.
+
+Related issues:
+- [FLINK-13123: Align Stop/Cancel Commands in CLI and REST Interface and Improve Documentation](https://issues.apache.org/jira/browse/FLINK-13123)
+- [FLINK-11458: Add TERMINATE/SUSPEND Job with Savepoint](https://issues.apache.org/jira/browse/FLINK-11458)
+
+### Network stack
+
+A few changes in the network stack related to changes in the threading model of `StreamTask` to a mailbox-based approach
+requires close attention to some related configuration:
+
+- Due to changes in the lifecycle management of result partitions, partition requests as well as re-triggers will now
+happen sooner. Therefore, it is possible that some jobs with long deployment times and large state might start failing
+more frequently with `PartitionNotFound` exceptions compared to previous versions. If that's the case, users should
+increase the value of `taskmanager.network.request-backoff.max` in order to have the same effective partition
+request timeout as it was prior to 1.9.0.
+
+- To avoid a potential deadlock, a timeout has been added for how long a task will wait for assignment of exclusive
+memory segments. The default timeout is 30 seconds, and is configurable via `taskmanager.network.memory.exclusive-buffers-request-timeout-ms`.
+It is possible that for some previously working deployments this default timeout value is too low
+and might have to be increased.
+
+Please also notice that several network I/O metrics have had their scope changed. See the [1.9 metrics documentation](https://ci.apache.org/projects/flink/flink-docs-master/monitoring/metrics.html)
+for which metrics are affected. In 1.9.0, these metrics will still be available under their previous scopes, but this
+may no longer be the case in future versions.
+
+Related issues:
+- [FLINK-13013: Make sure that SingleInputGate can always request partitions](https://issues.apache.org/jira/browse/FLINK-13013)
+- [FLINK-12852: Deadlock occurs when requiring exclusive buffer for RemoteInputChannel](https://issues.apache.org/jira/browse/FLINK-12852)
+- [FLINK-12555: Introduce an encapsulated metric group layout for shuffle API and deprecate old one](https://issues.apache.org/jira/browse/FLINK-12555)
+
+### AsyncIO
+
+Due to a bug in the `AsyncWaitOperator`, in 1.9.0 the default chaining behaviour of the operator is now changed so
+that it is never chained after another operator. This should not be problematic for migrating from older version
+snapshots as long as an uid was assigned to the operator. If an uid was not assigned to the operator, please see
+the instructions [here](https://ci.apache.org/projects/flink/flink-docs-release-1.9/ops/upgrading.html#matching-operator-state)
+for a possible workaround.
+
+Related issues:
+- [FLINK-13063: AsyncWaitOperator shouldn't be releasing checkpointingLock](https://issues.apache.org/jira/browse/FLINK-13063)
+
+### Connectors and Libraries
+
+#### Introduced `KafkaSerializationSchema` to fully replace `KeyedSerializationSchema`
+
+The universal `FlinkKafkaProducer` (in `flink-connector-kafka`) supports a new `KafkaSerializationSchema` that will
+fully replace `KeyedSerializationSchema` in the long run. This new schema allows directly generating Kafka
+`ProducerRecord`s for sending to Kafka, therefore enabling the user to use all available Kafka features (in the context
+of Kafka records).
+
+#### Dropped connectors and libraries
+
+- The Elasticsearch 1 connector has been dropped and will no longer receive patches. Users may continue to use the
+connector from a previous series (like 1.8) with newer versions of Flink. It is being dropped due to being used
+significantly less than more recent versions (Elasticsearch versions 2.x and 5.x are downloaded 4 to 5 times more), and
+hasn't seen any development for over a year.
+
+- The older Python APIs for batch and streaming have been removed and will no longer receive new patches.
+A new API is being developed based on the Table API as part of [FLINK-12308: Support python language in Flink Table API](https://issues.apache.org/jira/browse/FLINK-12308).
+Existing users may continue to use these older APIs with future versions of Flink by copying both the `flink-streaming-python`
+and `flink-python` jars into the `/lib` directory of the distribution and the corresponding start scripts `pyflink-stream.sh`
+and `pyflink.sh` into the `/bin` directory of the distribution.
+
+- The older machine learning libraries have been removed and will no longer receive new patches.
+This is due to efforts towards a new Table-based machine learning library ([FLIP-39](https://docs.google.com/document/d/1StObo1DLp8iiy0rbukx8kwAJb0BwDZrQrMWub3DzsEo/edit)).
+Users can still use the 1.8 version of the legacy library if their projects still rely on it.
+
+Related issues:
+- [FLINK-11693: Add KafkaSerializationSchema that directly uses ProducerRecord](https://issues.apache.org/jira/browse/FLINK-11693)
+- [FLINK-12151: Drop Elasticsearch 1 connector](https://issues.apache.org/jira/browse/FLINK-12151)
+- [FLINK-12903: Remove legacy flink-python APIs](https://issues.apache.org/jira/browse/FLINK-12903)
+- [FLINK-12308: Support python language in Flink Table API](https://issues.apache.org/jira/browse/FLINK-12308)
+- [FLINK-12597: Remove the legacy flink-libraries/flink-ml](https://issues.apache.org/jira/browse/FLINK-12597)
+
+### MapR dependency removed
+
+Dependency on MapR vendor-specific artifacts has been removed, by changing the MapR filesystem connector to work
+purely based on reflection. This does not introduce any regession in the support for the MapR filesystem.
+The decision to remove hard dependencies on the MapR artifacts was made due to very flaky access to the secure https
+endpoint of the MapR artifact repository, and affected build stability of Flink.
+
+Related issues:
+- [FLINK-12578: Use secure URLs for Maven repositories](https://issues.apache.org/jira/browse/FLINK-12578)
+- [FLINK-13499: Remove dependency on MapR artifact repository](https://issues.apache.org/jira/browse/FLINK-13499)
+
+### StateDescriptor interface change
+
+Access to the state serializer in `StateDescriptor` is now modified from protected to private access. Subclasses
+should use the `StateDescriptor#getSerializer()` method as the only means to obtain the wrapped state serializer.
+
+Related issues:
+- [FLINK-12688: Make serializer lazy initialization thread safe in StateDescriptor](https://issues.apache.org/jira/browse/FLINK-12688)
+
+### Web UI dashboard
+
+The web frontend of Flink has been updated to use the latest Angular version (7.x). The old frontend remains
+available in Flink 1.9.x, but will be removed in a later Flink release once the new frontend is considered stable.
+
+Related issues:
+- [FLINK-10705: Rework Flink Web Dashoard](https://issues.apache.org/jira/browse/FLINK-10705)