This is an automated email from the ASF dual-hosted git repository.
dwysakowicz 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 26da1bf [FLINK-22373][docs] Add Flink 1.13 release notes
26da1bf is described below
commit 26da1bf6aab2c8cad4f36cc541c19fda11a6921a
Author: Dawid Wysakowicz <[email protected]>
AuthorDate: Tue Apr 20 15:08:55 2021 +0200
[FLINK-22373][docs] Add Flink 1.13 release notes
This closes #15687
---
docs/content.zh/release-notes/flink-1.13.md | 282 ++++++++++++++++++++++++++++
docs/content/_index.md | 2 +-
docs/content/release-notes/flink-1.13.md | 282 ++++++++++++++++++++++++++++
3 files changed, 565 insertions(+), 1 deletion(-)
diff --git a/docs/content.zh/release-notes/flink-1.13.md
b/docs/content.zh/release-notes/flink-1.13.md
new file mode 100644
index 0000000..601cff0
--- /dev/null
+++ b/docs/content.zh/release-notes/flink-1.13.md
@@ -0,0 +1,282 @@
+---
+title: "Release Notes - Flink 1.13"
+---
+<!--
+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.
+-->
+
+# Release Notes - Flink 1.13
+
+These release notes discuss important aspects, such as configuration,
behavior, or dependencies,
+that changed between Flink 1.12 and Flink 1.13. Please read these notes
carefully if you are
+planning to upgrade your Flink version to 1.13.
+
+### Failover
+
+#### Remove state.backend.async option.
+
+##### [FLINK-21935](https://issues.apache.org/jira/browse/FLINK-21935)
+
+The `state.backend.async` option is deprecated. Snapshots are always
asynchronous now (as they were
+by default before) and there is no option to configure a synchronous snapshot
any more.
+
+The constructors of `FsStateBackend` and `MemoryStateBackend` that take a flag
for sync/async
+snapshots are kept for API compatibility, but the flags are ignored now.
+
+#### Unify binary format for Keyed State savepoints
+
+##### [FLINK-20976](https://issues.apache.org/jira/browse/FLINK-20976)
+
+Flink’s savepoint binary format is unified across all state backends. That
means you can take a
+savepoint with one state backend and then restore it using another.
+
+If you want to switch the state backend you should first upgrade your Flink
version to 1.13, then
+take a savepoint with the new version, and only after that, you can restore it
with a different
+state backend.
+
+#### FailureRateRestartBackoffTimeStrategy allows one less restart than
configured
+
+##### [FLINK-20752](https://issues.apache.org/jira/browse/FLINK-20752)
+
+The Failure Rate Restart Strategy was allowing 1 less restart per interval
than configured. Users
+wishing to keep the current behavior should reduce the maximum number of
allowed failures per
+interval by 1.
+
+#### Support rescaling for Unaligned Checkpoints
+
+##### [FLINK-17979](https://issues.apache.org/jira/browse/FLINK-17979)
+
+While recovering from unaligned checkpoints, users can now change the
parallelism of the job. This
+change allows users to quickly upscale the job under backpressure.
+
+### SQL
+
+#### Officially deprecate the legacy planner
+
+##### [FLINK-21709](https://issues.apache.org/jira/browse/FLINK-21709)
+
+The old planner of the Table & SQL API is deprecated and will be dropped in
Flink 1.14. This means
+that both the BatchTableEnvironment and DataSet API interop are reaching end
of life. Use the
+unified TableEnvironment for batch and stream processing with the new planner,
or the DataStream API
+in batch execution mode.
+
+#### Use TIMESTAMP_LTZ as return type for function PROCTIME()
+
+##### [FLINK-21714](https://issues.apache.org/jira/browse/FLINK-21714)
+
+Before Flink 1.13, the function return type of `PROCTIME()` is `TIMESTAMP`,
and the return value is
+the `TIMESTAMP` in UTC time zone, e.g. the wall-clock shows `2021-03-01
12:00:00` at Shanghai,
+however the `PROCTIME()` displays `2021-03-01 04:00:00` which is wrong. Flink
1.13 fixes this issue
+and uses `TIMESTAMP_LTZ` type as return type of `PROCTIME()`, users don't need
to deal time zone
+problems anymore.
+
+#### Support defining event time attribute on TIMESTAMP_LTZ column
+
+##### [FLINK-20387](https://issues.apache.org/jira/browse/FLINK-20387)
+
+Support defining event time attribute on TIMESTAMP_LTZ column, base on this,
Flink SQL gracefully
+support the Daylight Saving Time.
+
+#### Correct function
CURRENT_TIMESTAMP/CURRENT_TIME/CURRENT_DATE/LOCALTIME/LOCALTIMESTAMP/NOW()
+
+##### [FLINK-21713](https://issues.apache.org/jira/browse/FLINK-21713)
+
+The value of time function CURRENT_TIMESTAMP and NOW() are corrected from UTC
time with `TIMESTAMP`
+type to epoch time with `TIMESTAMP_LTZ` type. Time function LOCALTIME,
LOCALTIMESTAMP, CURRENT_DATE,
+CURRENT_TIME, CURRENT_TIMESTAMP and NOW() are corrected from evaluates for per
record in batch mode
+to evaluate once at query-start for batch job.
+
+#### Disable problematic cast conversion between NUMERIC type and TIMESTAMP
type
+
+##### [FLINK-21698](https://issues.apache.org/jira/browse/FLINK-21698)
+
+The CAST operation between `NUMERIC` type and `TIMESTAMP` type is problematic
and is disabled now,
+e.g.
+`CAST(numeric AS TIMESTAMP(3))` is disabled and should use
`TO_TIMESTAMP(FROM_UNIXTIME(numeric))`
+instead.
+
+#### Support USE MODULES syntax
+
+##### [FLINK-21298](https://issues.apache.org/jira/browse/FLINK-21298)
+
+The term MODULES is a reserved keyword now. Use backticks to escape column
names and other
+identifiers with this name.
+
+#### Update TableResult.collect()/TableResult.print() to the new type system
+
+##### [FLINK-20613](https://issues.apache.org/jira/browse/FLINK-20613)
+
+`Table.execute().collect()` might return slightly different results for column
types and row kind.
+The most important differences include:
+
+* Structured types are represented as POJOs of the original class and not Row
anymore.
+* Raw types are serialized according to the configuration in TableConfig.
+
+
+#### Update the Row.toString method
+
+##### [FLINK-18090](https://issues.apache.org/jira/browse/FLINK-18090)
+
+The `Row.toSting()` method has been reworked. This is an incompatible change.
If the legacy
+representation is still required for tests, the old behavior can be restored
via the flag
+`RowUtils.USE_LEGACY_TO_STRING` for the local JVM. However, relying on the
row's string
+representation for tests is not a good idea in general as field data types are
not verified.
+
+#### Support start SQL Client with an initialization SQL file
+
+##### [FLINK-20320](https://issues.apache.org/jira/browse/FLINK-20320)
+
+The `sql-client-defaults.yaml` YAML file is deprecated and not provided in the
release package. To
+be compatible, it's still supported to initialize the SQL Client with the YAML
file if manually
+provided. But it's recommend to use the new introduced `-i` startup option to
execute an
+initialization SQL file to setup the SQL Client session. The so-called
initialization SQL file can
+use Flink DDLs to define available catalogs, table sources and sinks,
user-defined functions, and
+other properties required for execution and deployment. The support of legacy
SQL Client YAML file
+will be totally dropped in Flink 1.14.
+
+#### Hive dialect no longer supports Flink syntax for DML and DQL
+
+##### [FLINK-21808](https://issues.apache.org/jira/browse/FLINK-21808)
+
+Hive dialect supports HiveQL for DML and DQL. Please switch to default dialect
in order to write in
+Flink syntax.
+
+### Runtime
+
+#### BoundedOneInput.endInput is called when taking synchronous savepoint
+
+##### [FLINK-21132](https://issues.apache.org/jira/browse/FLINK-21132)
+
+`endInput()` is not called anymore (on BoundedOneInput and BoundedMultiInput)
when the job is
+stopping with savepoint.
+
+#### Remove JobManagerOptions.SCHEDULING_STRATEGY
+
+##### [FLINK-20591](https://issues.apache.org/jira/browse/FLINK-20591)
+
+The configuration parameter `jobmanager.scheduler.scheduling-strategy` has
been removed, because
+the `legacy` scheduler has been removed from Flink 1.13.0.
+
+#### Warn user if System.exit() is called in user code
+
+##### [FLINK-15156](https://issues.apache.org/jira/browse/FLINK-15156)
+
+A new configuration value `cluster.intercept-user-system-exit` allows to log a
warning, or throw an
+exception if user code calls `System.exit()`.
+
+This feature is not covering all locations in Flink where user code is
executed. It just adds the
+infrastructure for such an interception. We are tracking this improvement in
+[FLINK-21307](https://issues.apache.org/jira/browse/FLINK-21307).
+
+### Docker
+
+#### Consider removing automatic configuration fo number of slots from docker
+
+##### [FLINK-21036](https://issues.apache.org/jira/browse/FLINK-21036)
+
+The docker images no longer set the default number of taskmanager slots to the
number of CPU cores.
+This behavior was inconsistent with all other deployment methods and ignored
any limits on the CPU
+usage set via docker.
+
+#### Rework jemalloc switch to use an environment variable
+
+##### [FLINK-21034](https://issues.apache.org/jira/browse/FLINK-21034)
+
+The docker switch for disabling the jemalloc memory allocator has been
reworked from a script
+argument to an environment variable called DISABLE_JEMALLOC. If set to "true"
jemalloc will not be
+enabled.
+
+### Connectors
+
+#### Remove swift FS filesystem
+
+##### [FLINK-21819](https://issues.apache.org/jira/browse/FLINK-21819)
+
+The Swift filesystem is no longer being actively developed and has been
removed from the project and
+distribution.
+
+##### [FLINK-22133](https://issues.apache.org/jira/browse/FLINK-22133)
+The unified source API for connectors has a minor breaking change. The
`SplitEnumerator.snapshotState()`
+method was adjusted to accept the *Checkpoint ID* of the checkpoint for which
the snapshot is created.
+
+### Monitoring & debugging
+
+#### Introduce latency tracking state
+
+##### [FLINK-21736](https://issues.apache.org/jira/browse/FLINK-21736)
+
+State access latency metrics are introduced to track all kinds of keyed state
access to help debug
+state performance. This feature is not enabled by default and can be turned on
by
+setting `state.backend.latency-track.keyed-state-enabled` to true.
+
+#### Support for CPU flame graphs in web UI
+
+##### [FLINK-13550](https://issues.apache.org/jira/browse/FLINK-13550)
+
+Flink now offers flame graphs for each node in the job graph. Please enable
this experimental feature
+by setting the respective configuration flag `rest.flamegraph.enabled`.
+
+#### Display last n exceptions/causes for job restarts in Web UI
+
+##### [FLINK-6042](https://issues.apache.org/jira/browse/FLINK-6042)
+
+Flink exposes the exception history now through the REST API and the UI. The
amount of most-recently
+handled exceptions that shall be tracked can be defined through
`web.exception-history-size`.
+Some values of the exception history's REST API Json response are deprecated
as part of this effort.
+
+#### Create backPressuredTimeMsPerSecond metric
+
+##### [FLINK-20717](https://issues.apache.org/jira/browse/FLINK-20717)
+
+Previously `idleTimeMsPerSecond` was defined as the time task spent waiting
for either the input or
+the back pressure. Now `idleTimeMsPerSecond` excludes back pressured time, so
if the task is back
+pressured it is not idle. The back pressured time is now measured separately
+as `backPressuredTimeMsPerSecond`.
+
+#### Enable log4j2 monitor interval by default
+
+##### [FLINK-20510](https://issues.apache.org/jira/browse/FLINK-20510)
+
+The Log4j support for updating the Log4j configuration at runtime has been
enabled by default. The
+configuration files are checked for changes every 30 seconds.
+
+#### ZooKeeper quorum fails to start due to missing log4j library
+
+##### [FLINK-20404](https://issues.apache.org/jira/browse/FLINK-20404)
+
+The Zookeeper scripts in the Flink distribution have been modified to disable
the Log4j JMX
+integration due to an incompatibility between Zookeeper 3.4 and Log4j 2. To
re-enable this feature,
+remove the line in the `zookeeper.sh` file that sets
`zookeeper.jmx.log4j.disable`.
+
+#### Expose stage of task initialization
+
+##### [FLINK-17012](https://issues.apache.org/jira/browse/FLINK-17012)
+
+Task's RUNNING state was split into two states: INITIALIZING and RUNNING. Task
is INITIALIZING while
+state is initialising and in case of unaligned checkpoints, until all the
in-flight data has been
+recovered.
+
+### Deployment
+
+#### Officially deprecate Mesos support
+
+##### [FLINK-22352](https://issues.apache.org/jira/browse/FLINK-22352)
+
+The community decided to deprecate the Apache Mesos support for Apache Flink.
It is subject to
+removal in the future. Users are encouraged to switch to a different resource
manager.
+
diff --git a/docs/content/_index.md b/docs/content/_index.md
index b842d35..aef1997 100644
--- a/docs/content/_index.md
+++ b/docs/content/_index.md
@@ -83,6 +83,6 @@ Release notes cover important changes between Flink versions.
Please read them c
For some reason Hugo will only allow linking to the
release notes if there is a leading '/' and file extension.
-->
-See the release notes for [Flink 1.12]({{< ref "/release-notes/flink-1.12.md"
>}}), [Flink 1.11]({{< ref "/release-notes/flink-1.11.md" >}}), [Flink
1.10]({{< ref "/release-notes/flink-1.10.md" >}}), [Flink 1.9]({{< ref
"/release-notes/flink-1.9.md" >}}), [Flink 1.8]({{< ref
"/release-notes/flink-1.8.md" >}}), or [Flink 1.7]({{< ref
"/release-notes/flink-1.7.md" >}}).
+See the release notes for [Flink 1.13]({{< ref "/release-notes/flink-1.13.md"
>}}), [Flink 1.12]({{< ref "/release-notes/flink-1.12.md" >}}), [Flink
1.11]({{< ref "/release-notes/flink-1.11.md" >}}), [Flink 1.10]({{< ref
"/release-notes/flink-1.10.md" >}}), [Flink 1.9]({{< ref
"/release-notes/flink-1.9.md" >}}), [Flink 1.8]({{< ref
"/release-notes/flink-1.8.md" >}}), or [Flink 1.7]({{< ref
"/release-notes/flink-1.7.md" >}}).
{{< /columns >}}
diff --git a/docs/content/release-notes/flink-1.13.md
b/docs/content/release-notes/flink-1.13.md
new file mode 100644
index 0000000..601cff0
--- /dev/null
+++ b/docs/content/release-notes/flink-1.13.md
@@ -0,0 +1,282 @@
+---
+title: "Release Notes - Flink 1.13"
+---
+<!--
+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.
+-->
+
+# Release Notes - Flink 1.13
+
+These release notes discuss important aspects, such as configuration,
behavior, or dependencies,
+that changed between Flink 1.12 and Flink 1.13. Please read these notes
carefully if you are
+planning to upgrade your Flink version to 1.13.
+
+### Failover
+
+#### Remove state.backend.async option.
+
+##### [FLINK-21935](https://issues.apache.org/jira/browse/FLINK-21935)
+
+The `state.backend.async` option is deprecated. Snapshots are always
asynchronous now (as they were
+by default before) and there is no option to configure a synchronous snapshot
any more.
+
+The constructors of `FsStateBackend` and `MemoryStateBackend` that take a flag
for sync/async
+snapshots are kept for API compatibility, but the flags are ignored now.
+
+#### Unify binary format for Keyed State savepoints
+
+##### [FLINK-20976](https://issues.apache.org/jira/browse/FLINK-20976)
+
+Flink’s savepoint binary format is unified across all state backends. That
means you can take a
+savepoint with one state backend and then restore it using another.
+
+If you want to switch the state backend you should first upgrade your Flink
version to 1.13, then
+take a savepoint with the new version, and only after that, you can restore it
with a different
+state backend.
+
+#### FailureRateRestartBackoffTimeStrategy allows one less restart than
configured
+
+##### [FLINK-20752](https://issues.apache.org/jira/browse/FLINK-20752)
+
+The Failure Rate Restart Strategy was allowing 1 less restart per interval
than configured. Users
+wishing to keep the current behavior should reduce the maximum number of
allowed failures per
+interval by 1.
+
+#### Support rescaling for Unaligned Checkpoints
+
+##### [FLINK-17979](https://issues.apache.org/jira/browse/FLINK-17979)
+
+While recovering from unaligned checkpoints, users can now change the
parallelism of the job. This
+change allows users to quickly upscale the job under backpressure.
+
+### SQL
+
+#### Officially deprecate the legacy planner
+
+##### [FLINK-21709](https://issues.apache.org/jira/browse/FLINK-21709)
+
+The old planner of the Table & SQL API is deprecated and will be dropped in
Flink 1.14. This means
+that both the BatchTableEnvironment and DataSet API interop are reaching end
of life. Use the
+unified TableEnvironment for batch and stream processing with the new planner,
or the DataStream API
+in batch execution mode.
+
+#### Use TIMESTAMP_LTZ as return type for function PROCTIME()
+
+##### [FLINK-21714](https://issues.apache.org/jira/browse/FLINK-21714)
+
+Before Flink 1.13, the function return type of `PROCTIME()` is `TIMESTAMP`,
and the return value is
+the `TIMESTAMP` in UTC time zone, e.g. the wall-clock shows `2021-03-01
12:00:00` at Shanghai,
+however the `PROCTIME()` displays `2021-03-01 04:00:00` which is wrong. Flink
1.13 fixes this issue
+and uses `TIMESTAMP_LTZ` type as return type of `PROCTIME()`, users don't need
to deal time zone
+problems anymore.
+
+#### Support defining event time attribute on TIMESTAMP_LTZ column
+
+##### [FLINK-20387](https://issues.apache.org/jira/browse/FLINK-20387)
+
+Support defining event time attribute on TIMESTAMP_LTZ column, base on this,
Flink SQL gracefully
+support the Daylight Saving Time.
+
+#### Correct function
CURRENT_TIMESTAMP/CURRENT_TIME/CURRENT_DATE/LOCALTIME/LOCALTIMESTAMP/NOW()
+
+##### [FLINK-21713](https://issues.apache.org/jira/browse/FLINK-21713)
+
+The value of time function CURRENT_TIMESTAMP and NOW() are corrected from UTC
time with `TIMESTAMP`
+type to epoch time with `TIMESTAMP_LTZ` type. Time function LOCALTIME,
LOCALTIMESTAMP, CURRENT_DATE,
+CURRENT_TIME, CURRENT_TIMESTAMP and NOW() are corrected from evaluates for per
record in batch mode
+to evaluate once at query-start for batch job.
+
+#### Disable problematic cast conversion between NUMERIC type and TIMESTAMP
type
+
+##### [FLINK-21698](https://issues.apache.org/jira/browse/FLINK-21698)
+
+The CAST operation between `NUMERIC` type and `TIMESTAMP` type is problematic
and is disabled now,
+e.g.
+`CAST(numeric AS TIMESTAMP(3))` is disabled and should use
`TO_TIMESTAMP(FROM_UNIXTIME(numeric))`
+instead.
+
+#### Support USE MODULES syntax
+
+##### [FLINK-21298](https://issues.apache.org/jira/browse/FLINK-21298)
+
+The term MODULES is a reserved keyword now. Use backticks to escape column
names and other
+identifiers with this name.
+
+#### Update TableResult.collect()/TableResult.print() to the new type system
+
+##### [FLINK-20613](https://issues.apache.org/jira/browse/FLINK-20613)
+
+`Table.execute().collect()` might return slightly different results for column
types and row kind.
+The most important differences include:
+
+* Structured types are represented as POJOs of the original class and not Row
anymore.
+* Raw types are serialized according to the configuration in TableConfig.
+
+
+#### Update the Row.toString method
+
+##### [FLINK-18090](https://issues.apache.org/jira/browse/FLINK-18090)
+
+The `Row.toSting()` method has been reworked. This is an incompatible change.
If the legacy
+representation is still required for tests, the old behavior can be restored
via the flag
+`RowUtils.USE_LEGACY_TO_STRING` for the local JVM. However, relying on the
row's string
+representation for tests is not a good idea in general as field data types are
not verified.
+
+#### Support start SQL Client with an initialization SQL file
+
+##### [FLINK-20320](https://issues.apache.org/jira/browse/FLINK-20320)
+
+The `sql-client-defaults.yaml` YAML file is deprecated and not provided in the
release package. To
+be compatible, it's still supported to initialize the SQL Client with the YAML
file if manually
+provided. But it's recommend to use the new introduced `-i` startup option to
execute an
+initialization SQL file to setup the SQL Client session. The so-called
initialization SQL file can
+use Flink DDLs to define available catalogs, table sources and sinks,
user-defined functions, and
+other properties required for execution and deployment. The support of legacy
SQL Client YAML file
+will be totally dropped in Flink 1.14.
+
+#### Hive dialect no longer supports Flink syntax for DML and DQL
+
+##### [FLINK-21808](https://issues.apache.org/jira/browse/FLINK-21808)
+
+Hive dialect supports HiveQL for DML and DQL. Please switch to default dialect
in order to write in
+Flink syntax.
+
+### Runtime
+
+#### BoundedOneInput.endInput is called when taking synchronous savepoint
+
+##### [FLINK-21132](https://issues.apache.org/jira/browse/FLINK-21132)
+
+`endInput()` is not called anymore (on BoundedOneInput and BoundedMultiInput)
when the job is
+stopping with savepoint.
+
+#### Remove JobManagerOptions.SCHEDULING_STRATEGY
+
+##### [FLINK-20591](https://issues.apache.org/jira/browse/FLINK-20591)
+
+The configuration parameter `jobmanager.scheduler.scheduling-strategy` has
been removed, because
+the `legacy` scheduler has been removed from Flink 1.13.0.
+
+#### Warn user if System.exit() is called in user code
+
+##### [FLINK-15156](https://issues.apache.org/jira/browse/FLINK-15156)
+
+A new configuration value `cluster.intercept-user-system-exit` allows to log a
warning, or throw an
+exception if user code calls `System.exit()`.
+
+This feature is not covering all locations in Flink where user code is
executed. It just adds the
+infrastructure for such an interception. We are tracking this improvement in
+[FLINK-21307](https://issues.apache.org/jira/browse/FLINK-21307).
+
+### Docker
+
+#### Consider removing automatic configuration fo number of slots from docker
+
+##### [FLINK-21036](https://issues.apache.org/jira/browse/FLINK-21036)
+
+The docker images no longer set the default number of taskmanager slots to the
number of CPU cores.
+This behavior was inconsistent with all other deployment methods and ignored
any limits on the CPU
+usage set via docker.
+
+#### Rework jemalloc switch to use an environment variable
+
+##### [FLINK-21034](https://issues.apache.org/jira/browse/FLINK-21034)
+
+The docker switch for disabling the jemalloc memory allocator has been
reworked from a script
+argument to an environment variable called DISABLE_JEMALLOC. If set to "true"
jemalloc will not be
+enabled.
+
+### Connectors
+
+#### Remove swift FS filesystem
+
+##### [FLINK-21819](https://issues.apache.org/jira/browse/FLINK-21819)
+
+The Swift filesystem is no longer being actively developed and has been
removed from the project and
+distribution.
+
+##### [FLINK-22133](https://issues.apache.org/jira/browse/FLINK-22133)
+The unified source API for connectors has a minor breaking change. The
`SplitEnumerator.snapshotState()`
+method was adjusted to accept the *Checkpoint ID* of the checkpoint for which
the snapshot is created.
+
+### Monitoring & debugging
+
+#### Introduce latency tracking state
+
+##### [FLINK-21736](https://issues.apache.org/jira/browse/FLINK-21736)
+
+State access latency metrics are introduced to track all kinds of keyed state
access to help debug
+state performance. This feature is not enabled by default and can be turned on
by
+setting `state.backend.latency-track.keyed-state-enabled` to true.
+
+#### Support for CPU flame graphs in web UI
+
+##### [FLINK-13550](https://issues.apache.org/jira/browse/FLINK-13550)
+
+Flink now offers flame graphs for each node in the job graph. Please enable
this experimental feature
+by setting the respective configuration flag `rest.flamegraph.enabled`.
+
+#### Display last n exceptions/causes for job restarts in Web UI
+
+##### [FLINK-6042](https://issues.apache.org/jira/browse/FLINK-6042)
+
+Flink exposes the exception history now through the REST API and the UI. The
amount of most-recently
+handled exceptions that shall be tracked can be defined through
`web.exception-history-size`.
+Some values of the exception history's REST API Json response are deprecated
as part of this effort.
+
+#### Create backPressuredTimeMsPerSecond metric
+
+##### [FLINK-20717](https://issues.apache.org/jira/browse/FLINK-20717)
+
+Previously `idleTimeMsPerSecond` was defined as the time task spent waiting
for either the input or
+the back pressure. Now `idleTimeMsPerSecond` excludes back pressured time, so
if the task is back
+pressured it is not idle. The back pressured time is now measured separately
+as `backPressuredTimeMsPerSecond`.
+
+#### Enable log4j2 monitor interval by default
+
+##### [FLINK-20510](https://issues.apache.org/jira/browse/FLINK-20510)
+
+The Log4j support for updating the Log4j configuration at runtime has been
enabled by default. The
+configuration files are checked for changes every 30 seconds.
+
+#### ZooKeeper quorum fails to start due to missing log4j library
+
+##### [FLINK-20404](https://issues.apache.org/jira/browse/FLINK-20404)
+
+The Zookeeper scripts in the Flink distribution have been modified to disable
the Log4j JMX
+integration due to an incompatibility between Zookeeper 3.4 and Log4j 2. To
re-enable this feature,
+remove the line in the `zookeeper.sh` file that sets
`zookeeper.jmx.log4j.disable`.
+
+#### Expose stage of task initialization
+
+##### [FLINK-17012](https://issues.apache.org/jira/browse/FLINK-17012)
+
+Task's RUNNING state was split into two states: INITIALIZING and RUNNING. Task
is INITIALIZING while
+state is initialising and in case of unaligned checkpoints, until all the
in-flight data has been
+recovered.
+
+### Deployment
+
+#### Officially deprecate Mesos support
+
+##### [FLINK-22352](https://issues.apache.org/jira/browse/FLINK-22352)
+
+The community decided to deprecate the Apache Mesos support for Apache Flink.
It is subject to
+removal in the future. Users are encouraged to switch to a different resource
manager.
+
