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Jonathan Ellis commented on CASSANDRA-4310:
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The problem is that for common workloads we expect most L0 sstables to overlap
with all L1 sstables. So there's very limited parallelism you can introduce in
the L0 -> L1 stage, which is the biggest bottleneck.
> Multiple independent Level Compactions in Parallel(Useful for SSD).
> --------------------------------------------------------------------
>
> Key: CASSANDRA-4310
> URL: https://issues.apache.org/jira/browse/CASSANDRA-4310
> Project: Cassandra
> Issue Type: New Feature
> Components: Core
> Affects Versions: 1.1.1, 1.1.2
> Reporter: sankalp kohli
> Labels: compaction, features, leveled, performance, ssd
>
> Problem: If you are inserting data into cassandra and level compaction cannot
> catchup, you will create lot of files in L0.
> Here is a solution which will help here and also increase the performance of
> level compaction.
> We can do many compactions in parallel for unrelated data.
> 1) For no over lapping levels. Ex: when L0 stable is compacting with L1, we
> can do compactions in other levels like L2 and L3 if they are eligible.
> 2) We can also do compactions with files in L1 which are not participating in
> L0 compactions.
> This is specially useful if you are using SSD and is not bottlenecked by IO.
> I am seeing this issue in my cluster. The compactions pending are more than
> 50k and the disk usage is not that much(I am using SSD).
> I am doing multithreaded to true and also not throttling the IO by putting
> the value as 0.
>
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