Roman Khachatryan created FLINK-26590:
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Summary: Triggered checkpoints can be delayed by discarding shared
state
Key: FLINK-26590
URL: https://issues.apache.org/jira/browse/FLINK-26590
Project: Flink
Issue Type: Improvement
Components: Runtime / Checkpointing
Affects Versions: 1.15.0, 1.14.3
Reporter: Roman Khachatryan
Assignee: Roman Khachatryan
Fix For: 1.16.0
Quick note: CheckpointCleaner is not involved here.
When a checkpoint is subsumed, SharedStateRegistry schedules its unused shared
state for async deletion. It uses common IO pool for this and adds a Runnable
per state handle. ( see SharedStateRegistryImpl.scheduleAsyncDelete)
When a checkpoint is started, CheckpointCoordinator uses the same thread pool
to initialize the location for it. (see
CheckpointCoordinator.initializeCheckpoint)
The thread pool is of fixed size
[jobmanager.io-pool.size|https://nightlies.apache.org/flink/flink-docs-master/docs/deployment/config/#jobmanager-io-pool-size];
by default it's the number of CPU cores) and uses FIFO queue for tasks.
When there is a spike in state deletion, the next checkpoint is delayed waiting
for an available IO thread.
Back-pressure seems reasonable here (similar to CheckpointCleaner); however,
this shared state deletion could be spread across multiple subsequent
checkpoints, not neccesarily the next one.
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I believe the issue is an pre-existing one; but it particularly affects
changelog state backend, because 1) such spikes are likely there; 2) workloads
are latency sensitive.
In the tests, checkpoint duration grows from seconds to minutes immediately
after the materialization.
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