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From Robert Coli <rc...@digg.com>
Subject Re: Nodes getting slowed down after a few days of smooth operation
Date Mon, 11 Oct 2010 17:05:13 GMT
  On 10/11/10 7:13 AM, Ran Tavory wrote:
> After a node gets restarted it compacts the sstable files on disk. I'm 
> not sure whether compactions always take place after restart, maybe 
> it's just minor compactions, I'm a little confused here, but my story 
> would work best if (major) compactions were always to run at server 
> restart.
Node startup contains (among other steps) :

- commit log replay
- memtable flush of replayed transactions

The memtable flush can and does trigger minor compactions, and this is 
almost certainly what you're seeing.

I have wondered before whether there is any technical reason why the 
commit log replay should end with a flush, and from what I can tell, 
there isn't one other than the general goal of not having a large commit 
log. My personal feeling is that the last thing you want your production 
node doing after you've restarted it  (blowing out the internal key and 
row caches) is compacting and blowing out your only remaining cache (the 
OS page cache) as a result. If this is a problem for others in 
production, I could submit a JIRA with a patch to disable the memtable 
flush part of startup?

=Rob

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