[jira] [Updated] (CASSANDRA-16261) Prevent unbounded number of flushing tasks

["Michael Semb Wever (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CASSANDRA-16261?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Michael Semb Wever updated CASSANDRA-16261:
-------------------------------------------
    Fix Version/s:     (was: 3.11.x)
                       (was: 3.0.x)
                   3.0.24
                   3.11.10

> Prevent unbounded number of flushing tasks
> ------------------------------------------
>
>                 Key: CASSANDRA-16261
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-16261
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Legacy/Local Write-Read Paths
>            Reporter: Ekaterina Dimitrova
>            Assignee: Ekaterina Dimitrova
>            Priority: Normal
>             Fix For: 3.0.24, 3.11.10, 4.0-rc1, 4.0
>
>
> The cleaner thread is not prevented from queueing an unbounded number of flushing tasks for memtables that are almost empty.
> This patch adds a mechanism to track the number of pending flushing
> tasks in the memtable cleaner. Above the maximum number (2x the flushing
> threads by default), only memtables using at least MCT memory will be
> flushed, where MCT stands for Memory Cleanup Threshold.
> This patch also fixes a possible problem tracking the memory marked as
> "reclaiming" in the memtable allocators and pool. Writes that complete
> only after a memtable has been scheduled for flushing, did not report
> their memory as reclaiming. Normally this should be a small value of no
> consequence, but if the flushing tasks are blocked for a long period,
> and there is a sufficient number of writes, or these writes use
> a sufficiently large quantity of memory, this would cause the memtable
> cleaning algorithm to schedule repeated flushing tasks because the used
> memory is always > reclaiming memory + MCT.



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