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From "Aleksey Yeschenko (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-6506) counters++ split counter context shards into separate cells
Date Mon, 24 Mar 2014 13:45:44 GMT


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:
>             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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