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From "Benedict (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-9708) Serialize ClusteringPrefixes in batches
Date Mon, 13 Jul 2015 08:44:04 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-9708?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14624373#comment-14624373
] 

Benedict commented on CASSANDRA-9708:
-------------------------------------

FTR, dtests failed in cassci after I made some minor tweaks to the implementation, so I'm
rerunning them (it looks like it may be an environment issue).

I'll hold off on adding unit tests for the obscure case of serializing more than 32 items,
until we can decide if we actually want to support such a wacky schema....

> Serialize ClusteringPrefixes in batches
> ---------------------------------------
>
>                 Key: CASSANDRA-9708
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-9708
>             Project: Cassandra
>          Issue Type: Sub-task
>          Components: Core
>            Reporter: Benedict
>            Assignee: Benedict
>             Fix For: 3.0.0 rc1
>
>
> Typically we will have very few clustering prefixes to serialize, however in theory they
are not constrained (or are they, just to a very large number?). Currently we encode a fat
header for all values up front (two bits per value), however those bits will typically be
zero, and typically we will have only a handful (perhaps 1 or 2) of values.
> This patch modifies the encoding to batch the prefixes in groups of up to 32, along with
a header that is vint encoded. Typically this will result in a single byte per batch, but
will consume up to 9 bytes if some of the values have their flags set. If we have more than
32 columns, we just read another header. This means we incur no garbage, and compress the
data on disk in many cases where we have more than 4 clustering components.
> I do wonder if we shouldn't impose a limit on clustering columns, though: If you have
more than a handful merge performance is going to disintegrate. 32 is probably well in excess
of what we should be seeing in the wild anyway.



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