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From "Yuki Morishita (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-4894) log number of combined/merged rows during a compaction
Date Wed, 19 Dec 2012 13:05:12 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-4894?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13535925#comment-13535925
] 

Yuki Morishita commented on CASSANDRA-4894:
-------------------------------------------

OK, I will commit this with the change in the log sentence to "Compaction merge counts: [x,
x, ...]" then.
                
> log number of combined/merged rows during a compaction
> ------------------------------------------------------
>
>                 Key: CASSANDRA-4894
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4894
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Matthew F. Dennis
>            Assignee: Yuki Morishita
>            Priority: Minor
>             Fix For: 1.2.1
>
>         Attachments: 4894-1.2.txt
>
>
> we already log some details about compactions but it would be useful to know how many
rows were merged (resulting in "useful" work) and how many were unique (representing "wasted
work").
> the simple approach requires two additional counters (one for unique rows, one for merged
rows).  As the merge join is progressing if two or more rows are combined, tick the joined
counter.  If a row is simply copied tick the unique counter.
> a more complete solution would be to keep a separate count for each number of merges.
 This would require number_of_files_being_merged counters.  If no rows were merged, tick counters[0],
if two rows were merged tick counters[1] and so on 

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