Bruno Cadonna created KAFKA-15297:
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Summary: Cache flush order might not be topological order
Key: KAFKA-15297
URL: https://issues.apache.org/jira/browse/KAFKA-15297
Project: Kafka
Issue Type: Bug
Components: streams
Affects Versions: 3.4.0
Reporter: Bruno Cadonna
Attachments: minimal_example.png
The flush order of the state store caches in Kafka Streams might not correspond
to the topological order of the state stores in the topology. The order depends
on how the processors and state stores are added to the topology.
In some cases downstream state stores might be flushed before upstream state
stores. That means, that during a commit records in upstream caches might end
up in downstream caches that have already been flushed during the same commit.
If a crash happens at that point, those records in the downstream caches are
lost. Those records are lost for two reasons:
1. Records in caches are only changelogged after they are flushed from the
cache. However, the downstream caches have already been flushed and they will
not be flushed again during the same commit.
2. The offsets of the input records that caused the records that now are
blocked in the downstream caches are committed during the same commit and so
they will not be re-processed after the crash.
An example for a topology where the flush order of the caches is wrong is the
following:
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