Re: [PERFORM] shared_buffers in 8.3 w/ lots of RAM on dedicated PG machine

2008-02-18 Thread Greg Smith
On Mon, 18 Feb 2008, Peter Schuller wrote: Am I interpreting that correctly in that dirty buffers need to be flushed to disk at checkpoints? That makes perfect sense - but why would that not be the case with OS buffers? All the dirty buffers in the cache are written out as part of the checkp

Re: [PERFORM] shared_buffers in 8.3 w/ lots of RAM on dedicated PG machine

2008-02-17 Thread Peter Schuller
> PostgreSQL only uses direct I/O for writing to the WAL; everything else > goes through the regular OS buffer cache unless you force it to do > otherwise at the OS level (like some Solaris setups do with > forcedirectio). This is one reason it still make not make sense to give > an extremely high

Re: [PERFORM] shared_buffers in 8.3 w/ lots of RAM on dedicated PG machine

2008-02-15 Thread Erik Jones
On Feb 15, 2008, at 12:42 PM, Joshua D. Drake wrote: -BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On Fri, 15 Feb 2008 12:37:10 -0600 Erik Jones <[EMAIL PROTECTED]> wrote: (welll, forced to) migrate to a new system with a sane drive configuration. The old set up was done horribly by a sysadm

Re: [PERFORM] shared_buffers in 8.3 w/ lots of RAM on dedicated PG machine

2008-02-15 Thread Jignesh K. Shah
Greg Smith wrote: On Fri, 15 Feb 2008, Peter Schuller wrote: Or is it a matter of PostgreSQL doing non-direct I/O, such that anything cached in shared_buffers will also be cached by the OS? PostgreSQL only uses direct I/O for writing to the WAL; everything else goes through the regular OS

Re: [PERFORM] shared_buffers in 8.3 w/ lots of RAM on dedicated PG machine

2008-02-15 Thread Joshua D. Drake
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On Fri, 15 Feb 2008 12:37:10 -0600 Erik Jones <[EMAIL PROTECTED]> wrote: >(welll, forced > to) migrate to a new system with a sane drive configuration. The > old set up was done horribly by a sysadmin who's no longer with us > who set us up with a R

Re: [PERFORM] shared_buffers in 8.3 w/ lots of RAM on dedicated PG machine

2008-02-15 Thread Erik Jones
On Feb 15, 2008, at 12:06 PM, Josh Berkus wrote: On Friday 15 February 2008 06:29, Greg Smith wrote: PostgreSQL only uses direct I/O for writing to the WAL; everything else goes through the regular OS buffer cache unless you force it to do otherwise at the OS level (like some Solaris setups

Re: [PERFORM] shared_buffers in 8.3 w/ lots of RAM on dedicated PG machine

2008-02-15 Thread Josh Berkus
On Friday 15 February 2008 06:29, Greg Smith wrote: > PostgreSQL only uses direct I/O for writing to the WAL; everything else > goes through the regular OS buffer cache unless you force it to do > otherwise at the OS level (like some Solaris setups do with > forcedirectio). Also, note that even wh

Re: [PERFORM] shared_buffers in 8.3 w/ lots of RAM on dedicated PG machine

2008-02-15 Thread Greg Smith
On Fri, 15 Feb 2008, Peter Schuller wrote: Or is it a matter of PostgreSQL doing non-direct I/O, such that anything cached in shared_buffers will also be cached by the OS? PostgreSQL only uses direct I/O for writing to the WAL; everything else goes through the regular OS buffer cache unless y

Re: [PERFORM] shared_buffers in 8.3 w/ lots of RAM on dedicated PG machine

2008-02-15 Thread Peter Schuller
> PostgreSQL still depends on the OS for file access and caching. I > think that the current recommendation is to have up to 25% of your > RAM in the shared buffer cache. This feels strange. Given a reasonable amount of RAM (let's say 8 GB in this case), I cannot imagine why 75% of that would be e

Re: [PERFORM] shared_buffers in 8.3 w/ lots of RAM on dedicated PG machine

2008-02-15 Thread Kenneth Marshall
On Fri, Feb 15, 2008 at 01:35:29PM +0100, Peter Schuller wrote: > Hello, > > my impression has been that in the past, there has been a general > semi-consensus that upping shared_buffers to use the majority of RAM > has not generally been recommended, with reliance on the buffer cache > instead be