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https://issues.apache.org/jira/browse/CASSANDRA-4894?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13535899#comment-13535899
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Matthew F. Dennis commented on CASSANDRA-4894:
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{quote}
we haven't really concerned ourselves with machine parseability so far
{quote}
that is a mistake. I'm not saying it should be the highest priority or hold up
changes but it should always be considered (on at least a best effort basis).
{quote}
I would in fact be in favor of saving compaction stats in a System table
{quote}
+1
CASSANDRA-5078
even ignoring the machine readable aspect though I want to be able to derive
meaning from the lines at a glance (until CASSANDRA-5078 is done and it's
exposed via nodetool, OPSC, etc) and the compact bracketed format makes that
easier.
> 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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