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https://issues.apache.org/jira/browse/CASSANDRA-4894?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13535835#comment-13535835
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Matthew F. Dennis commented on CASSANDRA-4894:
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I like the original bracketed format better. The verbose option is hard to
parse at a glance. likewise, dropping the zeros would make things more
complicated to compare quickly. the bracketed syntax is easy to
grep/script/compare/parse/etc.
maybe call it "compaction merge counts" instead of "merged row stats" though
(so if we had more stats later we don't have to come up with a different name)
and then make sure the docs are indexable for "compaction merge counts". Also
need to be clear in the docs that counts[0] is just copied, counts[1] is merged
two rows, etc ...
> 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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