Re: [HACKERS] [hackers]development suggestion needed

At 10:11 AM 1/14/00 -0500, Tom Lane wrote:
>Oleg Bartunov <oleg(at)sai(dot)msu(dot)su> writes:
>>> The selects that such sites spew forth are handled wonderfully
>>> by Postgres now, with MVCC and the change that stops the update
>>> of pg_log after read-only selects.
>> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>> Does plain 6.5.3 handle read-only selects in this way ?
>
>AFAIR that logic is in 6.5.*. (Vadim would remember better, since he
>put it in.)

It is. I'd notice right away if it wasn't, the decibel level on my
little database server would go 'way up because it went 'way down when
I applied the patch to my 6.5 beta. It sits six inches from me so
I'd know for sure!

>It occurs to me that the no-log-update logic could probably be improved
>on. The test to see whether a log update is needed looks at whether any
>buffers have been written. A SELECT that marks someone else's tuples as
>known-committed will look like it needs to be committed in pg_log
>... but it doesn't really need it. Perhaps Vadim is planning to fix
>this in the WAL rewrite.

No idea if he is or isn't, but the patch is very simple and is based
on whether or not buffers got dirty, not whether or not the select
itself changed anything, IIRC.

- Don Baccus, Portland OR <dhogaza(at)pacifier(dot)com>
Nature photos, on-line guides, Pacific Northwest
Rare Bird Alert Service and other goodies at
http://donb.photo.net.