[jira] [Commented] (CASSANDRA-7545) Hints for a down node are written to a single partition in system.hints on the coordinator leading to contention

["graham sanderson (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-7545?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14061492#comment-14061492 ] 

graham sanderson commented on CASSANDRA-7545:
---------------------------------------------

Per [~jbellis]

"Unfortunately I don't think we can do much for hint partitioning.
It's too late for a schema change in 2.1, and 3.0 we're already
planning to move to file-based hint storage."

Short of doing some sort of hideous procedural mutation of the real UUID into a fixed number of derived but likely to be unique UUIDs, there isn't much we can do, so we will wait on CASSANDRA-6230, and hope a fix to CASSANDRA-7546 helps


> Hints for a down node are written to a single partition in system.hints on the coordinator leading to contention
> ----------------------------------------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-7545
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-7545
>             Project: Cassandra
>          Issue Type: Bug
>            Reporter: graham sanderson
>
> The worst side effect is potentially orders of magnitude larger than suspected memory allocation due to a race condition updating the columns in the memtable (see CASSANDRA-7546)
> That said, having so many hints in a single partition has other negative side effects (non linear growth of sorted tree data structure overhead in memtable, just plain large number of tombstones in a row etc.)
> Ideally, the hints would be partitioned by both the nodeUUID, and a fixed number of (say 4) bits of a hash of the original rowmutation's partition key... even this small spreading of load has a significant improvement.



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