Branimir Lambov created CASSANDRA-21041:
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Summary: SSTable overlap statistics
Key: CASSANDRA-21041
URL: https://issues.apache.org/jira/browse/CASSANDRA-21041
Project: Apache Cassandra
Issue Type: Improvement
Components: Local/Compaction, Local/Compaction/UCS
Reporter: Branimir Lambov
When trying to evaluate the effect of compaction and its settings, perhaps the
most relevant information is the amount of overlap between sstables, i.e. the
number of sstables that have to be queried to serve any request for a specific
partition. We do not currently present this information for any compaction
strategy.
For some strategies this can be organized by level, and specifically for UCS,
by shard.
[This patch in the DataStax
repository|https://github.com/datastax/cassandra/commit/c7d6f082e9eef8f9121ef271495e9a2469bde671]
implements such a statistic for UCS, which outputs overlap per level as
{code}
Max overlap map for density.blobs:
all: 26, per shard: [11, 11, 17, 17, 14, 14, 20, 20, 17, 17, 23, 23, 20, 20,
26, 26]
unrepaired:0: 18, per shard: [6, 10, 14, 18]
unrepaired:1: 9, per shard: [6, 9, 5, 8, 4, 7, 3, 6]
unrepaired:2: 3, per shard: [3, 3, 3, 3, 3, 3, 2, 2, 3, 3, 3, 3, 3, 3, 2, 2,
3, 3, 3, 3, 3, 3, 2, 2, 3, 3, 3, 3, 3, 3, 2, 2]
{code}.
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