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From "Vladimir Ozerov (JIRA)" <j...@apache.org>
Subject [jira] [Closed] (IGNITE-9590) MVCC: Cleanup old rows in the vacuum thread.
Date Mon, 11 Mar 2019 07:18:00 GMT

     [ https://issues.apache.org/jira/browse/IGNITE-9590?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Vladimir Ozerov closed IGNITE-9590.

> MVCC: Cleanup old rows in the vacuum thread.
> --------------------------------------------
>                 Key: IGNITE-9590
>                 URL: https://issues.apache.org/jira/browse/IGNITE-9590
>             Project: Ignite
>          Issue Type: Improvement
>          Components: mvcc
>            Reporter: Roman Kondakov
>            Priority: Major
>              Labels: performance
> When updating writer thread should iterate over the set of the last versions in order
to find an appropriate version for its MVCC snapshot. During this iteration it collects
invisible to anybody versions (their xid_max version is less than cleanup). When all outdated
versions found, writer thread cleanups these rows - removes it from indexes and from pagestore.
> It would be more efficient if writer thread does not cleanup old rows by itself, but
rather delegate it to vacuum workers: instead of cleaning just put it to cleanup queue. 
> in case of significant backpressure during active updates, when cleanup workers can't
keep up with removing outdated rows and cleanup queue is too big, writer threads can cleanup
this rows by itself to prevent memory and performance problems.
> Upd: Also we can acquire checkpointReadLock for a fix-sized batch of cleaning versions
Vacuum.cleanup() rather than for every single remove or rather than removing all outdated
version at once. See TxLog.removeUntil() method.

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