Details
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Bug
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Status: Resolved
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Low
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Resolution: Fixed
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None
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None
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Low
Description
Most of Cassandra assumes that ThreadPoolExecutor handles tasks by starting with Core threads, adding threads up to Max as tasks arrive, then queuing any additional. This is not correct:
If fewer than corePoolSize threads are running, the Executor always prefers adding a new thread rather than queuing.
If corePoolSize or more threads are running, the Executor always prefers queuing a request rather than adding a new thread.
If a request cannot be queued, a new thread is created unless this would exceed maximumPoolSize, in which case, the task will be rejected.
CASSANDRA-2178 fixed this in one place but made it worse by default since most people run with a single data dir, meaning as soon as you have multiple CFs flushing (or a single one with indexes) then you will start blocking writes.