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From "Jeremiah Jordan (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-5371) Perform size-tiered compactions in L0
Date Thu, 21 Mar 2013 19:33:16 GMT


Jeremiah Jordan commented on CASSANDRA-5371:

I could see this possibly helping if you left the non L0 alone and went to STCS for L0 until
the write load stopped. But you have to come up with a heuristic to know when to shut off
LCS.  So a cluster with a periodic write load, which was too high for LCS's increased IO needs,
would revert to STCS of L0 only until the load dropped.  You would then have to play catchup
shoving all that L0 data into the other levels. I could see use cases where this would be
useful, such as periodic large data dumps into a cluster. You would have to be careful that
there was enough down time between dumps for LCS to catchup.
> Perform size-tiered compactions in L0
> -------------------------------------
>                 Key: CASSANDRA-5371
>                 URL:
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>            Reporter: Jonathan Ellis
>            Assignee: T Jake Luciani
>             Fix For: 2.0
> If LCS gets behind, read performance deteriorates as we have to check bloom filters on
man sstables in L0.  For wide rows, this can mean having to seek for each one since the BF
doesn't help us reject much.
> Performing size-tiered compaction in L0 will mitigate this until we can catch up on merging
it into higher levels.

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