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Date: Mon, 24 Mar 2014 13:45:44 +0000 (UTC)
From: "Aleksey Yeschenko (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
Message-ID: <JIRA.12685498.1387418927660.131211.1395668744379@arcas>
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Subject: [jira] [Commented] (CASSANDRA-6506) counters++ split counter
 context shards into separate cells
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    [ https://issues.apache.org/jira/browse/CASSANDRA-6506?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13945099#comment-13945099 ] 

Aleksey Yeschenko commented on CASSANDRA-6506:
----------------------------------------------

That's one of the differences between 2.0 and 2.1 - in 2.0 we localCopy() first, then reconcile(), and thus have to use the same allocator all the way, but in 2.1 we reconcile() first, and localCopy() the result.

> counters++ split counter context shards into separate cells
> -----------------------------------------------------------
>
>                 Key: CASSANDRA-6506
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6506
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Aleksey Yeschenko
>            Assignee: Aleksey Yeschenko
>             Fix For: 2.1 beta2
>
>
> This change is related to, but somewhat orthogonal to CASSANDRA-6504.
> Currently all the shard tuples for a given counter cell are packed, in sorted order, in one binary blob. Thus reconciling N counter cells requires allocating a new byte buffer capable of holding the union of the two context's shards N-1 times.
> For writes, in post CASSANDRA-6504 world, it also means reading more data than we have to (the complete context, when all we need is the local node's global shard).
> Splitting the context into separate cells, one cell per shard, will help to improve this. We did a similar thing with super columns for CASSANDRA-3237. Incidentally, doing this split is now possible thanks to CASSANDRA-3237.
> Doing this would also simplify counter reconciliation logic. Getting rid of old contexts altogether can be done trivially with upgradesstables.
> In fact, we should be able to put the logical clock into the cell's timestamp, and use regular Cell-s and regular Cell reconcile() logic for the shards, especially once we get rid of the local/remote shards some time in the future (until then we still have to differentiate between global/remote/local shards and their priority rules).


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