[jira] [Updated] (CASSANDRA-14210) Optimize SSTables upgrade task scheduling

["Marcus Eriksson (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CASSANDRA-14210?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Marcus Eriksson updated CASSANDRA-14210:
----------------------------------------
       Resolution: Fixed
    Fix Version/s:     (was: 4.x)
                   3.11.3
                   3.0.17
                   4.0
    Reproduced In: 3.0.15, 2.2.11  (was: 2.2.11, 3.0.15)
           Status: Resolved  (was: Ready to Commit)

committed as {{f88ec9357de406daad0f795951f17e5f854ade10}} - thanks!

> Optimize SSTables upgrade task scheduling
> -----------------------------------------
>
>                 Key: CASSANDRA-14210
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-14210
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Compaction
>            Reporter: Oleksandr Shulgin
>            Assignee: Kurt Greaves
>            Priority: Major
>             Fix For: 4.0, 3.0.17, 3.11.3
>
>
> When starting the SSTable-rewrite process by running {{nodetool upgradesstables --jobs N}}, with N > 1, not all of the provided N slots are used.
> For example, we were testing with {{concurrent_compactors=5}} and {{N=4}}.  What we observed both for version 2.2 and 3.0, is that initially all 4 provided slots are used for "Upgrade sstables" compactions, but later when some of the 4 tasks are finished, no new tasks are scheduled immediately.  It takes the last of the 4 tasks to finish before new 4 tasks would be scheduled.  This happens on every node we've observed.
> This doesn't utilize available resources to the full extent allowed by the --jobs N parameter.  In the field, on a cluster of 12 nodes with 4-5 TiB data each, we've seen that the whole process was taking more than 7 days, instead of estimated 1.5-2 days (provided there would be close to full N slots utilization).
> Instead, new tasks should be scheduled as soon as there is a free compaction slot.
> Additionally, starting from the biggest SSTables could further reduce the total time required for the whole process to finish on any given node.



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