Message-ID: <4EAACA17.7010503@engene.se>
Date: Fri, 28 Oct 2011 17:28:23 +0200
From: Marcus Engene <mengpg2@engene.se>
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To: pgsql-performance@postgresql.org
Subject: WAL in RAM
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Hi list,

Every now and then I have write peaks which causes annoying delay on my 
website. No particular reason it seems, just that laws of probability 
dictates that there will be peaks every now and then.

Anyway, thinking of ways to make the peaks more bareable, I saw the new 
9.1 feature to bypass WAL. Problems is mainly that some statistics 
tables ("x users clicked this link this month") clog the write cache, 
not more important writes. I could live with restoring a nightly dump of 
these tables and loose a days worth of logs.

Though not keen on jumping over to early major versions an old idea of 
putting WAL in RAM came back. Not RAM in main memory but some thingie 
pretending to be a drive with proper battery backup.

a) It seems to exist odd hardware with RAM modules and if lucky also battery
b) Some drive manufactureres have done hybird ram-spindle drives 
(compare with possibly more common ssd-spindle hybrides).

b) sounds slightly more appealing since it basically means I put 
everything on those drives and it magically is faster. The a) 
alternatives also seemed to be non ECC which is a no-no and disturbing.

Does anyone here have any recommendations here?

Pricing is not very important but reliability is.

Thanks,
Marcus