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From Edward Capriolo <>
Subject Re: LeveledCompaction and/or SnappyCompressor causing memory pressure during repair
Date Sat, 10 Mar 2012 22:38:15 GMT
The only downside of compression is it does cause more memory
pressure. I can imagine something like repair could confound this.
Since it would seem like building the merkle tree would involve
decompressing every block on disk.

I have been attempting to determine if the block size being larger or
smaller has any effect on memory pressure.

On Sat, Mar 10, 2012 at 4:50 PM, Peter Schuller
<> wrote:
>> However, when I run a repair my CMS usage graph no longer shows sudden drops
>> but rather gradual slopes and only manages to clear around 300MB each GC.
>> This seems to occur on 2 other nodes in my cluster around the same time, I
>> assume this is because they're the replicas (we use 3 replicas). Parnew
>> collections look about the same on my graphs with or without repair running
>> so no trouble there so far as I can tell.
> I don't know why leveled/snappy would affect it, but disregarding
> that, I would have been suggesting that you are seeing additional heap
> usage because of long-running repairs retaining sstables and delaying
> their unload/removal (index sampling/bloom filters filling your heap).
> If it really only happens for leveled/snappy however, I don't know
> what that might be caused by.
> --
> / Peter Schuller (@scode,

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