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guo Maxwell commented on CASSANDRA-21041:
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I've been thinking about this. In addition to outputting the number of
overlapping SSTables, would it be better to also include the range of
overlapping token range? For example, outputting it in JSON format, along with
the range of each overlapping token ranges and the number of overlapping
SSTables. Of course, the output results might be quite large. [~blambov] wdyt ?
> 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
> Assignee: guo Maxwell
> Priority: Normal
> Fix For: 6.x
>
> Attachments: overlap-graph.png
>
>
> 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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