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From "Sylvain Lebresne (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-4894) log number of combined/merged rows during a compaction
Date Wed, 19 Dec 2012 09:33:14 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-4894?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13535814#comment-13535814
] 

Sylvain Lebresne commented on CASSANDRA-4894:
---------------------------------------------

bq. I don't come up with good short description to put in that log line

This is not extremely short, but since the line logged is already pretty long, why not something
like:
{noformat}
... Time: 35ms. Row merged: 1 from 3 sstables, 12 from 2 sstables and 354 from 1 sstable.
{noformat}
And of course we can just skip the 0's in that case.


                
> 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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