Matthew F. Dennis created CASSANDRA-4894:
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Summary: 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
Reporter: Matthew F. Dennis
Priority: Critical
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 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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