Announcing the Release of Apache Flink 1.19

March 18, 2024 - Lincoln Lee (@lincoln_86xy)

The Apache Flink PMC is pleased to announce the release of Apache Flink 1.19.0. As usual, we are looking at a packed release with a wide variety of improvements and new features. Overall, 162 people contributed to this release completing 33 FLIPs and 600+ issues. Thank you!

Let’s dive into the highlights.

Flink SQL Improvements #

Custom Parallelism for Table/SQL Sources #

Now in Flink 1.19, you can set a custom parallelism for performance tuning via the scan.parallelism option. The first available connector is DataGen (Kafka connector is on the way). Here is an example using SQL Client:

-- set parallelism within the ddl
    order_number BIGINT,
    price        DECIMAL(32,2),
    buyer        ROW<first_name STRING, last_name STRING>,
    order_time   TIMESTAMP(3)
) WITH (
    'connector' = 'datagen',
    'scan.parallelism' = '4'

-- or set parallelism via dynamic table option
SELECT * FROM Orders /*+ OPTIONS('scan.parallelism'='4') */;

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Configurable SQL Gateway Java Options #

A new option for specifying the Java options is introduced in Flink 1.19, so you can fine-tune the memory settings, garbage collection behavior, and other relevant Java parameters for SQL Gateway.

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Configure Different State TTLs Using SQL Hint #

Starting from Flink 1.18, Table API and SQL users can set state time-to-live (TTL) individually for stateful operators via the SQL compiled plan. In Flink 1.19, users have a more flexible way to specify custom TTL values for regular joins and group aggregations directly within their queries by utilizing the STATE_TTL hint. This improvement means that you no longer need to alter your compiled plan to set specific TTLs for these frequently used operators. With the introduction of STATE_TTL hints, you can streamline your workflow and dynamically adjust the TTL based on your operational requirements.

Here is an example:

-- set state ttl for join
SELECT /*+ STATE_TTL('Orders'= '1d', 'Customers' = '20d') */ *
    ON Orders.o_custkey = Customers.c_custkey;

-- set state ttl for aggregation
SELECT /*+ STATE_TTL('o' = '1d') */ o_orderkey, SUM(o_totalprice) AS revenue
FROM Orders AS o
GROUP BY o_orderkey;

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Named Parameters for Functions and Procedures #

Named parameters now can be used when calling a function or stored procedure. With named parameters, users do not need to strictly specify the parameter position, just specify the parameter name and its corresponding value. At the same time, if non-essential parameters are not specified, they will default to being filled with null.

Here’s an example of defining a function with one mandatory parameter and two optional parameters using named parameters:

public static class NamedArgumentsTableFunction extends TableFunction<Object> {

			output = @DataTypeHint("STRING"),
			arguments = {
					@ArgumentHint(name = "in1", isOptional = false, type = @DataTypeHint("STRING")),
					@ArgumentHint(name = "in2", isOptional = true, type = @DataTypeHint("STRING")),
					@ArgumentHint(name = "in3", isOptional = true, type = @DataTypeHint("STRING"))})
	public void eval(String arg1, String arg2, String arg3) {
		collect(arg1 + ", " + arg2 + "," + arg3);


When calling the function in SQL, parameters can be specified by name, for example:

SELECT * FROM TABLE(myFunction(in1 => 'v1', in3 => 'v3', in2 => 'v2'));

Also the optional parameters can be omitted:

SELECT * FROM TABLE(myFunction(in1 => 'v1'));

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Window TVF Aggregation Features #

  • Supports SESSION Window TVF in Streaming Mode
    Now users can use SESSION Window TVF in streaming mode. A simple example is as follows:
-- session window with partition keys

-- apply aggregation on the session windowed table with partition keys
SELECT window_start, window_end, item, SUM(price) AS total_price
GROUP BY item, window_start, window_end;
  • Supports Changelog Inputs for Window TVF Aggregation
    Window aggregation operators (generated based on Window TVF Function) can now handle changelog streams (e.g., CDC data sources, etc.). Users are recommended to migrate from legacy window aggregation to the new syntax for more complete feature support.

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New UDF Type: AsyncScalarFunction #

The common UDF type ScalarFunction works well for CPU-intensive operations, but less well for IO bound or otherwise long-running computations. In Flink 1.19, we have a new AsyncScalarFunction which is a user-defined asynchronous ScalarFunction allows for issuing concurrent function calls asynchronously.

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Tuning: MiniBatch Optimization for Regular Joins #

The record amplification is a pain point when performing cascading joins in Flink, now in Flink 1.19, the new mini-batch optimization can be used for regular join to reduce intermediate result in such cascading join scenarios.

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Runtime & Coordination Improvements #

Dynamic Source Parallelism Inference for Batch Jobs #

In Flink 1.19, we have supported dynamic source parallelism inference for batch jobs, which allows source connectors to dynamically infer the parallelism based on the actual amount of data to consume. This feature is a significant improvement over previous versions, which only assigned a fixed default parallelism to source vertices. Source connectors need to implement the inference interface to enable dynamic parallelism inference. Currently, the FileSource connector has already been developed with this functionality in place. Additionally, the configuration will be used as the upper bound of source parallelism inference. And now it will not default to 1. Instead, if it is not set, the upper bound of allowed parallelism set via will be used. If that configuration is also not set, the default parallelism set via parallelism.default or StreamExecutionEnvironment#setParallelism() will be used instead.

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Starting with Flink 1.19, Flink has officially introduced full support for the standard YAML 1.2 syntax. The default configuration file has been changed to config.yaml and placed in the conf/ directory. Users should directly modify this file to configure Flink. If users want to use the legacy configuration file flink-conf.yaml, users just need to copy this file into the conf/ directory. Once the legacy configuration file flink-conf.yaml is detected, Flink will prioritize using it as the configuration file. And in the upcoming Flink 2.0, the flink-conf.yaml configuration file will no longer work.

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In Flink 1.19, we support triggering profiling at the JobManager/TaskManager level, allowing users to create a profiling instance with arbitrary intervals and event modes (supported by async-profiler). Users can easily submit profiles and export results in the Flink Web UI.

For example, users can simply submit a profiling instance with a specified period and mode by “Creating a Profiling Instance” after identifying a candidate TaskManager/JobManager with a performance bottleneck:

then easily download the interactive HTML file after the profiling instance is complete:

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New Config Options for Administrator JVM Options #

A set of administrator JVM options are available, which prepend the user-set extra JVM options for platform-wide JVM tuning.

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Beta Support for Java 21 #

Apache Flink was made ready to compile and run with Java 21. This feature is still in beta mode. Issues should be reported in Flink’s bug tracker.

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Checkpoints Improvements #

Using Larger Checkpointing Interval When Source is Processing Backlog #

IsProcessingBacklog is introduced to indicate whether a record should be processed with low latency or high throughput. Connector developers can update the Source implementation to utilize the SplitEnumeratorContext#setIsProcessingBacklog method to report whether the records are backlog records. Users can set the execution.checkpointing.interval-during-backlog to use a larger checkpoint interval to enhance the throughput while the job is processing backlog if the source is backlog-aware.

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CheckpointsCleaner Clean Individual Checkpoint States in Parallel #

Now when disposing of no longer needed checkpoints, every state handle/state file will be disposed in parallel by the ioExecutor, vastly improving the disposing speed of a single checkpoint (for large checkpoints the disposal time can be improved from 10 minutes to < 1 minute) . The old behavior can be restored by setting state.checkpoint.cleaner.parallel-mode to false.

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Trigger Checkpoints through Command Line Client #

The command line interface supports triggering a checkpoint manually. Usage:

./bin/flink checkpoint $JOB_ID [-full]

By specifying the ‘-full’ option, a full checkpoint is triggered. Otherwise an incremental checkpoint is triggered if the job is configured to take incremental ones periodically.

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Connector API Improvements #

New Interfaces to SinkV2 That Are Consistent with Source API #

In Flink 1.19, the SinkV2 API made some changes to align with Source API.
The following interfaces are deprecated: TwoPhaseCommittingSink, StatefulSink, WithPreWriteTopology, WithPreCommitTopology, WithPostCommitTopology.
The following new interfaces have been introduced: CommitterInitContext, CommittingSinkWriter, WriterInitContext, StatefulSinkWriter.
The following interface method’s parameter has been changed: Sink#createWriter.
The original interfaces will remain available during the 1.19 release line, but they will be removed in consecutive releases.

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New Committer Metrics to Track the Status of Committables #

The TwoPhaseCommittingSink#createCommitter method parameterization has been changed, a new CommitterInitContext parameter has been added. The original method will remain available during the 1.19 release line, but they will be removed in consecutive releases.

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Important Deprecations #

In preparation for the release of Flink 2.0 later this year, the community has decided to officially deprecate multiple APIs that were approaching end of life for a while.

Upgrade Notes #

The Flink community tries to ensure that upgrades are as seamless as possible. However, certain changes may require users to make adjustments to certain parts of the program when upgrading to version 1.19. Please refer to the release notes for a comprehensive list of adjustments to make and issues to check during the upgrading process.

List of Contributors #

The Apache Flink community would like to express gratitude to all the contributors who made this release possible:

Adi Polak, Ahmed Hamdy, Akira Ajisaka, Alan Sheinberg, Aleksandr Pilipenko, Alex Wu, Alexander Fedulov, Archit Goyal, Asha Boyapati, Benchao Li, Bo Cui, Cheena Budhiraja, Chesnay Schepler, Dale Lane, Danny Cranmer, David Moravek, Dawid Wysakowicz, Deepyaman Datta, Dian Fu, Dmitriy Linevich, Elkhan Dadashov, Eric Brzezenski, Etienne Chauchot, Fang Yong, Feng Jiajie, Feng Jin, Ferenc Csaky, Gabor Somogyi, Gyula Fora, Hang Ruan, Hangxiang Yu, Hanyu Zheng, Hjw, Hong Liang Teoh, Hongshun Wang, HuangXingBo, Jack, Jacky Lau, James Hughes, Jane Chan, Jerome Gagnon, Jeyhun Karimov, Jiabao Sun, JiangXin, Jiangjie (Becket) Qin, Jim Hughes, Jing Ge, Jinzhong Li, JunRuiLee, Laffery, Leonard Xu, Lijie Wang, Martijn Visser, Marton Balassi, Matt Wang, Matthias Pohl, Matthias Schwalbe, Matyas Orhidi, Maximilian Michels, Mingliang Liu, Máté Czagány, Panagiotis Garefalakis, ParyshevSergey, Patrick Lucas, Peter Huang, Peter Vary, Piotr Nowojski, Prabhu Joseph, Pranav Sharma, Qingsheng Ren, Robin Moffatt, Roc Marshal, Rodrigo Meneses, Roman, Roman Khachatryan, Ron, Rui Fan, Ruibin Xing, Ryan Skraba, Samrat002, Sergey Nuyanzin, Shammon FY, Shengkai, Stefan Richter, SuDewei, TBCCC, Tartarus0zm, Thomas Weise, Timo Walther, Varun, Venkata krishnan Sowrirajan, Vladimir Matveev, Wang FeiFan, Weihua Hu, Weijie Guo, Wencong Liu, Xiangyu Feng, Xianxun Ye, Xiaogang Zhou, Xintong Song, XuShuai, Xuyang, Yanfei Lei, Yangze Guo, Yi Zhang, Yu Chen, Yuan Mei, Yubin Li, Yuepeng Pan, Yun Gao, Yun Tang, Yuxin Tan, Zakelly, Zhanghao Chen, Zhu Zhu, archzi, bvarghese1, caicancai, caodizhou, dongwoo6kim, duanyc, eason.qin, fengjiajie, fengli, gongzhongqiang, gyang94, hejufang, jiangxin, jiaoqingbo, jingge, lijingwei.5018, lincoln lee, liuyongvs, luoyuxia, mimaomao, murong00, polaris6, pvary, sharath1709, simplejason, sunxia, sxnan, tzy123-123, wangfeifan, wangzzu, xiangyu0xf, xiarui, xingbo, xuyang, yeming, yhx, yinhan.yh, yunfan123, yunfengzhou-hub, yunhong, yuxia Luo, yuxiang, zoudan, 周仁祥, 曹帝胄, 朱通通, 马越