Roman Khachatryan created FLINK-26306:
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Summary: Triggered checkpoints can be delayed by discarding shared
state
Key: FLINK-26306
URL: https://issues.apache.org/jira/browse/FLINK-26306
Project: Flink
Issue Type: Bug
Components: Runtime / Checkpointing
Affects Versions: 1.14.3, 1.15.0
Reporter: Roman Khachatryan
Assignee: Roman Khachatryan
Fix For: 1.15.0
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.
I believe the issue is an old one.
But it particularly affects changelog state backend, because 1) such spikes are
likely; 2) workloads are latency sensitive.
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