I am implementing a new sql operator algorithm called full-disjunction.
I need to experiment with different environment conditions for
it and different cost considerations.
I can estimate the io cost by counting the operations of reading
and writing tuples from the database but it would be very unaccurate.
I am working on postgreSQL and it turns out it only guesstimate the io
cost of a query. Just a few prob:
- postgreSQL is MVCC and thus the tables could be larger than they
actually contain visible tuples.
- the tuples could occupy 4 times their size in the disk.
- what about caching, how does it helps, detters.
- debugging, to see I am not double reading.
and the list goes on...
PostgreSQL can compile In windows where at least on the surface
using the taskmanager related libraries I can access a process
read/write
io. however, I can never know whats with the background writer and it
has probably the same issues as in linux with counting those.
I am better off with linux where I can prove its not doing anything more
than it claims.
btw, I was talking about shutting the background writer completely...
but alternatively I can recompile postgreSQL with different modes of
opening files as you suggested. In the end it just uses fopen,open.
Regards,
tzahi.
> -----Original Message-----
> From: Muli Ben-Yehuda [mailto:[EMAIL PROTECTED]
> Sent: Thursday, January 13, 2005 10:17 AM
> To: Tzahi Fadida
> Cc: 'guy keren'; [email protected]
> Subject: Re: Getting io statistics on processes.
>
>
> On Thu, Jan 13, 2005 at 01:37:16AM +0200, Tzahi Fadida wrote:
>
> > maybe I should just disable the background writer and disable read
> > aheads. since I am working on a database, its doing its own caching.
> > can it be done?
>
> Possibly via some combinatino of O_DIRECT and O_SYNC.
>
> I think at this point Guy's email bears repeating - what
> exactly are you trying to do?
>
> Cheers,
> Muli
> --
> Muli Ben-Yehuda
> http://www.mulix.org | http://mulix.livejournal.com/
>
>
>
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