Re: 500 tpsQL + WAL log implementation

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@candle.pha.pa.us               |  (610)
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