[jira] [Created] (CASSANDRA-15836) nodetool garbagecollect could leave LCS level intact

["Tom van der Woerdt (Jira)" <ji...@apache.org>]

Tom van der Woerdt created CASSANDRA-15836:
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             Summary: nodetool garbagecollect could leave LCS level intact
                 Key: CASSANDRA-15836
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-15836
             Project: Cassandra
          Issue Type: Improvement
            Reporter: Tom van der Woerdt


The nodetool command `garbagecollect` will run a single-sstable compaction for every sstable in a cf, while using other sstables on the side to allow for dropping tombstoned data. However, in doing so, it resets all LCS levels back to 0, causing a significant write amplification.

Fundamentally there's no reason why LCS levels have to be changed here, since these are single-sstable compactions. When the expected reduction in data set size is small (say, 10%) it may be preferable for sstables to remain in place instead of having to go through the entire compaction process again.



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