Chinmay Kulkarni created PHOENIX-5945:
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Summary: TaskRegionObserver can kick off the same tasks multiple
times if SYSTEM.TASK has split
Key: PHOENIX-5945
URL: https://issues.apache.org/jira/browse/PHOENIX-5945
Project: Phoenix
Issue Type: Bug
Affects Versions: 4.15.0
Reporter: Chinmay Kulkarni
Fix For: 5.1.0, 4.16.0
We don't specify a split policy for
[SYSTEM.TASK|https://github.com/apache/phoenix/blob/5f9364db7e4925229704706e148e62f4cf4ec4c2/phoenix-core/src/main/java/org/apache/phoenix/query/QueryConstants.java#L381],
so by default it will be allowed to split. Now if SYSTEM.TASK spans multiple
regions, each region's
[postOpen|https://github.com/apache/phoenix/blob/5f9364db7e4925229704706e148e62f4cf4ec4c2/phoenix-core/src/main/java/org/apache/phoenix/coprocessor/TaskRegionObserver.java#L137]
schedules the SelfHealingTask at the specified interval and so [each region
will run a FTS on the
table|https://github.com/apache/phoenix/blob/5f9364db7e4925229704706e148e62f4cf4ec4c2/phoenix-core/src/main/java/org/apache/phoenix/coprocessor/TaskRegionObserver.java#L159]
and try to kick-off all the incomplete and non-failed tasks.
This can lead to the same tasks being kicked off multiple times as a corner
race condition in spite of [this
check|https://github.com/apache/phoenix/blob/5f9364db7e4925229704706e148e62f4cf4ec4c2/phoenix-core/src/main/java/org/apache/phoenix/coprocessor/TaskRegionObserver.java#L187-L195]
(which is another FTS) and also lead to unnecessary extra load on the server.
We do not explicitly outline that tasks need to be idempotent, so we should
handle this properly in the TaskRegionObserver so that each region is only
responsible for tasks lying within its boundaries.
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