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Re: WAL in RAM

From: Merlin Moncure <mmoncure(at)gmail(dot)com>
To: Marcus Engene <mengpg2(at)engene(dot)se>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: WAL in RAM
Date: 2011-10-28 16:11:41
Message-ID: CAHyXU0xNW6ihoqWMn7tyqP5iEsYB-63v=+FiGVXDkQtWiw=CtQ@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
On Fri, Oct 28, 2011 at 10:28 AM, Marcus Engene <mengpg2(at)engene(dot)se> wrote:
> 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.

Have you ruled out SSD?  They are a little new, but I'd be looking at
the Intel 710.  In every case I've seen SSD permanently ends I/O
issues.  DRAM storage solutions I find to be pricey and complicated
when there are so many workable flash options out now.

merlin

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  • WAL in RAM at 2011-10-28 15:28:23 from Marcus Engene

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