Re: Frequently updated tables

On Wed, Jun 09, 2004 at 01:41:27PM -0400, pgsql(at)mohawksoft(dot)com wrote:
> > On Wed, Jun 09, 2004 at 10:49:20PM +0800, Christopher Kings-Lynne wrote:

> > Also he said that the problem was solved with enough lazy VACUUM
> > scheduling. I don't understand why he doesn't want to use that
> > solution.
>
> Sigh, because vacuums take away from performance. Imagine a table that has
> to be updated on the order of a few thousand times a minute. Think about
> the drop in performance during the vacuum.
>
> On a one row table, vacuum is not so bad, but try some benchmarks on a
> table with a goodly number of rows.

Hmm, this can be a problem if VACUUM pollutes the shared buffer pool.
So what about a new buffer replacement policy that takes this into
account and is not fooled by VACUUM? This is already implemented in
7.5. Also, how about a background writer process that writes dirty
buffers so that backends don't have to wait for IO to complete when a
dirty buffer has to be written? This is also in current CVS.

Have you tried and measured how the current CVS code performs? Jan
Wieck reported a lot of performance improvement some time ago while he
was developing this. The code has changed since and I have not seen any
measurement.

--
Alvaro Herrera (<alvherre[a]dcc.uchile.cl>)
Oh, oh, las chicas galacianas, lo harán por las perlas,
¡Y las de Arrakis por el agua! Pero si buscas damas
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