Rui Fan created FLINK-32414: ------------------------------- Summary: Watermark alignment will cause flink jobs to hang forever when any source subtask has no SourceSplit Key: FLINK-32414 URL: https://issues.apache.org/jira/browse/FLINK-32414 Project: Flink Issue Type: Bug Affects Versions: 1.17.1, 1.16.2 Reporter: Rui Fan Assignee: Rui Fan Attachments: image-2023-06-22-22-43-59-671.png
Watermark alignment will cause flink jobs to hang forever when any source subtask has no SourceSplit. h1. Root cause: # [SourceOperator#emitLatestWatermark|https://github.com/apache/flink/blob/274aa0debffaa57926c474f11e36be753b49cbc5/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/operators/SourceOperator.java#L504] reports the lastEmittedWatermark to SourceCoordinator # If one subtask has no SourceSplit, the lastEmittedWatermark will be the [Watermark.UNINITIALIZED.getTimestamp()|https://github.com/apache/flink/blob/274aa0debffaa57926c474f11e36be753b49cbc5/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/operators/SourceOperator.java#L149] forever, it's Long.MIN_VALUE. # SourceCoordinator combines the watermark of all subtasks, and using the [minimum watermark|https://github.com/apache/flink/blob/274aa0debffaa57926c474f11e36be753b49cbc5/flink-runtime/src/main/java/org/apache/flink/runtime/source/coordinator/SourceCoordinator.java#L644] as the aggregated watermark. # Long.MIN_VALUE must be the minimum watermark, so the maxAllowedWatermark = Long.MIN_VALUE + maxAllowedWatermarkDrift, and [SourceCoordinator will announce it to all subtasks.|https://github.com/apache/flink/blob/274aa0debffaa57926c474f11e36be753b49cbc5/flink-runtime/src/main/java/org/apache/flink/runtime/source/coordinator/SourceCoordinator.java#L168] # The maxAllowedWatermark is very small, so all source subtasks will hang forever h1. How to reproduce? When the kafka partition number is less than the parallelism of kafka source. Here is a demo: [code link|https://github.com/1996fanrui/fanrui-learning/commit/24b707f7805b3a61a70df1c70c26f8e8a16b006b] * kafka partition is 1 * The paralleslism is 2 !image-2023-06-22-22-43-59-671.png! -- This message was sent by Atlassian Jira (v8.20.10#820010)