Piotr Nowojski created FLINK-30070:
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Summary: Create savepoints without side effects
Key: FLINK-30070
URL: https://issues.apache.org/jira/browse/FLINK-30070
Project: Flink
Issue Type: New Feature
Components: API / DataStream, Runtime / Checkpointing
Affects Versions: 1.14.6, 1.15.2, 1.16.0
Reporter: Piotr Nowojski
Side effects are any external state - a state that is stored not in Flink, but
in an external system, like for example connectors transactions (KafkaSink,
...).
We shouldn't be relaying on the external systems for storing part of the job's
state, especially for any long period of time. The most prominent issue is that
Kafka transactions can time out, leading to a data loss if transaction hasn't
been committed.
Stop-with-savepoint, currently guarantee that {{notifyCheckpointCompleted}}
call will be issued, so properly implemented operators are guaranteed to
committed it's state. However this information is currently not stored in the
checkpoint in any way ( FLINK-16419 ). Larger issue is how to deal with
savepoints, since there we currently do not have any guarantees that
transactions have been committed.
Some potential solution might be to expand API (like {{CheckpointedFunction}}
), to let the operators/functions know, that they should
close/commit/clear/deal with external state differently and use that API during
stop-with-savepoint + rework how regular savepoints are handled.
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