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Re: 500 tpsQL + WAL log implementation

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Jan Wieck <JanWieck(at)Yahoo(dot)com>
Cc: Curtis Faith <curtis(at)galtcapital(dot)com>,pgsql-hackers(at)postgresql(dot)org
Subject: Re: 500 tpsQL + WAL log implementation
Date: 2003-05-26 18:18:21
Message-ID: 200305261818.h4QIILx09692@candle.pha.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Jan Wieck wrote:
> Bruce Momjian wrote:
> > [...]
> > If we could somehow know the platter location, or tell the disk drive to
> > write it in several locations, whichever is closest, I think we would
> > have a real win.  However, I don't see any way of doing that.
> > 
> > Imagine what we could do with 8mb of battery-backed RAM!  This is sort
> > of what we are using WAL/disk for, and it really isn't very good at it.
> 
> Isn't that what modern disk drives have ... well, not exactly battery 
> backed, but actually the energy they have in the rotation is enough to 
> flush the "write cache" out to the surface and get the heads back into 
> the parking position in the case of a power loss.

That's what I am not sure about --- if those drives return a 'complete'
before getting the actual data on the drive, then we don't have a
rotational delay problem because it isn't waiting for the platter to
spin into place, _and_ the data is secure.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman(at)candle(dot)pha(dot)pa(dot)us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

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