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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] Commented: (CASSANDRA-2102) saved row cache doesn't save the cache
Date Thu, 10 Feb 2011 16:56:57 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-2102?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12993114#comment-12993114
] 

Jonathan Ellis commented on CASSANDRA-2102:
-------------------------------------------

I think you're right, if your cache is doing its job (high hit rate) then copy-before-insert
will be less copies than copy-for-local-operation.

> saved row cache doesn't save the cache
> --------------------------------------
>
>                 Key: CASSANDRA-2102
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-2102
>             Project: Cassandra
>          Issue Type: Bug
>    Affects Versions: 0.7.0
>            Reporter: Matthew F. Dennis
>            Assignee: Matthew F. Dennis
>             Fix For: 0.7.2
>
>         Attachments: 2102-cassandra-0.7-v2.txt, 2102-cassandra-0.7.txt
>
>
> saving row caches works by periodically iterating of the keySet() on the caches and writing
the keys for the cached contents to disk.  The cache keys are DecoratedKeys.  DecoratedKeys
contain a Token token and a ByteBuffer key.  The underlying buffer on the key gets reused
so the contents change.  This means that all the cache entries have distinct tokens but only
a handful of distinct key values.  This means that when the cache is loaded you only end up
loading a handful of keys instead of the ones actually in your cache.

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