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Björn Hegerfors commented on CASSANDRA-7272:
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I don't understand why major compaction for STCS isn't already optimal. I do
see why one might want to compact some but not all SSTables in a
multi-tombstone compaction (CASSANDRA-7019) (though DTCS should be a better fit
for anyone wanting this). But if every single SSTable is being rewritten to
disk, why not write them into one file? As far as I understand, the ultimate
goal of STCS is to be one SSTable. STCS only gets there, the natural way, once
in a blue moon. But that's the most optimal state that it can be in. Am I wrong?
The only explanation I can see for splitting the result of compacting all
SSTables into fragments, is if those fragments are:
1. Partitioned smartly. For example into separate token ranges (à la LCS),
timestamp ranges (à la DTCS) or clustering column ranges (which would be
interesting). Or a combination of these.
2. The structure upheld by the resulting fragments is not subsequently
demolished by the running compaction strategy going on with its usual business.
> Add "Major" Compaction to LCS
> ------------------------------
>
> Key: CASSANDRA-7272
> URL: https://issues.apache.org/jira/browse/CASSANDRA-7272
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: T Jake Luciani
> Assignee: Marcus Eriksson
> Priority: Minor
> Labels: compaction
> Fix For: 3.0
>
>
> LCS has a number of minor issues (maybe major depending on your perspective).
> LCS is primarily used for wide rows so for instance when you repair data in
> LCS you end up with a copy of an entire repaired row in L0. Over time if you
> repair you end up with multiple copies of a row in L0 - L5. This can make
> predicting disk usage confusing.
> Another issue is cleaning up tombstoned data. If a tombstone lives in level
> 1 and data for the cell lives in level 5 the data will not be reclaimed from
> disk until the tombstone reaches level 5.
> I propose we add a "major" compaction for LCS that forces consolidation of
> data to level 5 to address these.
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