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From "Aleksey Yeschenko (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-6880) counters++ lock on cells, not partitions
Date Fri, 28 Mar 2014 21:21:17 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-6880?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13951398#comment-13951398
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Aleksey Yeschenko commented on CASSANDRA-6880:
----------------------------------------------

The old (pre-1.2) index locks were per-keyspace. I'm more inclined to go global this time,
though. Whether to go 1024 * CW or higher is an open question though. FWIW I'm not committing
this until the current batch of CASSANDRA-6553 and the next one (with changed params + some
new tests) are run, so feel free to keep brainstorming here.

> counters++ lock on cells, not partitions
> ----------------------------------------
>
>                 Key: CASSANDRA-6880
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6880
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Aleksey Yeschenko
>            Assignee: Aleksey Yeschenko
>             Fix For: 2.1 beta2
>
>
> I'm starting to think that we should switch to locking by cells, not by partitions, when
updating counters.
> With the current 2.1 counters, if nothing changes, the new recommendation would become
"use smaller partitions, batch updates to the same partition", and that goes against what
we usually recommend:
> 1. Prefer wide partitions to narrow partitions
> 2. Don't batch counter updates (because you risk to exaggerate undercounting/overcounting
in case of a timeout)
> Locking on cells would cause C* to have to grab more locks for batch counter updates,
but would give us generally more predictable performance (independent of partition wideness),
and won't force people to remodel their data model if they have often concurrently-updated
counters in the same few wide partitions.
> (It's a small change, code-wise)



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