[jira] Commented: (CASSANDRA-1546) (Yet another) approach to counting

["zhu han (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-1546?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12915276#action_12915276 ] 

zhu han commented on CASSANDRA-1546:
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That's soooooo cool. Thank you. :-)

Does the lead replica has to iterate all SSTables,  and get the latest value of th counter before applying the decr/incr mutation?   If so, the read path can be a performance bottleneck.  But we can leverage some tricks: only the counter columns in the latest SSTable are valid and others in the old SSTable can be ignored safely. 

So, the frequently updated counter column can resides in memtable, and local read-modify-write operation only brings negligible performance lost. The counter update path is almost as fast as normal column update path.

I have no idea about the detail of the removal before incr/decr problem. But a quick solution could be let the deletion operation snapshots the current value of counter column,  write it in another column. Just let the read path to merge these columns, including different counter columns,  and the deletion snapshot column.

The deletion snapshot column are reconciled by the timestamp as usual. So if the counter is deleted multiple times, only the latest snapshot is kept and decreased from the merged counter value in read path.



> (Yet another) approach to counting
> ----------------------------------
>
>                 Key: CASSANDRA-1546
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-1546
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Core
>            Reporter: Sylvain Lebresne
>            Assignee: Sylvain Lebresne
>             Fix For: 0.7.0
>
>         Attachments: 0001-Remove-IClock-from-internals.patch, 0002-Counters.patch, 0003-Generated-thrift-files-changes.patch
>
>
> This could be described as a mix between CASSANDRA-1072 without clocks and CASSANDRA-1421.
> More details in the comment below.

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