[jira] [Commented] (CASSANDRA-8459) "autocompaction" on reads can prevent memtable space reclaimation

["Philo Yang (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-8459?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14242511#comment-14242511 ] 

Philo Yang commented on CASSANDRA-8459:
---------------------------------------

Hi, [~benedict], there is no node in my cluster that is unresponsive to dump the heap. But there are some hprof files dumped by +HeapDumpOnOutOfMemoryError automatically, are they helpful to you? If so I'll upload one of them.

> "autocompaction" on reads can prevent memtable space reclaimation
> -----------------------------------------------------------------
>
>                 Key: CASSANDRA-8459
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-8459
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>            Reporter: Benedict
>            Assignee: Benedict
>             Fix For: 2.1.3
>
>         Attachments: 8459.txt
>
>
> Memtable memory reclamation is dependent on reads always making progress, however on the collectTimeOrderedData critical path it is possible for the read to perform a _write_ inline, and for this write to block waiting for memtable space to be reclaimed. However the reclaimation is blocked waiting for this read to complete.
> There are a number of solutions to this, but the simplest is to make the defragmentation happen asynchronously, so the read terminates normally.



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