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From "Jonathan Ellis (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-4310) Multiple independent Level Compactions in Parallel
Date Mon, 08 Oct 2012 23:28:03 GMT


Jonathan Ellis commented on CASSANDRA-4310:

Looking good.

Pushed v4 to with some changes:

- made getNextBackgroundTask synchronized.  lets us not have to worry about subsets in markCompacting
(which we were handling incorrectly for user-defined compactions -- want to fail if we can't
do exactly what user asks for).
- made L0 do a best-effort job when L1 compactions get in the way of what it would prefer
to do
- skipped the initial overlapping-with-compaction difference in > L0 case since it gets
included in the check after union with overlapping in L+1
- added some @VisibleForTesting annotations

Also did some more cleanup of forceDeserialize and isCompactionInteresting in a separate commit.
> Multiple independent Level Compactions in Parallel
> --------------------------------------------------
>                 Key: CASSANDRA-4310
>                 URL:
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Core
>    Affects Versions: 1.0.0
>            Reporter: sankalp kohli
>            Assignee: Yuki Morishita
>              Labels: compaction, features, leveled, performance, ssd
>             Fix For: 1.2.1
>         Attachments: 4310.txt, 4310-v2.txt, 4310-v3.txt
> 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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