Re: PostgreSQL on 64 bit Linux

On 21 Aug 2006, at 10:48, mark@mark.mielke.cc wrote:

> On Mon, Aug 21, 2006 at 12:00:58PM +0300, Alexander Kirpa wrote:
> > > WRT 64-bit and Postgres, it depends on the CPU as to whether you
> > > see a simple performance benefit.  On the Opteron you will see a
> > > benefit when doing CPU bound work.  When doing the CPU portion,
> > > the additional registers of the Opteron running in 64-bit mode are
> > > used by the compiler to produce a 20-30% boost in performance.  On
> > > the Xeon in 64-bit mode, the same regions of execution will slow
> > > down by about 5%.
> > 
> > > Postgres benefits automatically from the larger memory addressing
> > > of the 64-bit kernel by using the larger I/O cache of Linux.
> > 
> > Main benefit Postgres in 64-bit mode possible only in case dedicated
> > DB server on system with RAM > 3GB and use most part of RAM for
> > shared buffers and avoid persistent moving buffers between OS cache
> > and shared memory. On system with RAM below 2-3GB to difficult found
> > serious gain of performance.
> 
> This is the main difference between PostgreSQL today - designed for
> 32-bit - when recompiled with a 64-bit compiler.
> 
> The additional registers are barely enough to counter the increased
> cost of processing in 64-bits.
> 
> Cheers,
> mark
Current 32-bit Postgres architecture allow use main benefit
of 64-bit OS - huge memory size for shared buffers.
At current time possible use 2G x 8KB = 16TB as shared memory
and regarding this issue need use (O_DIRECT) to avoid OS cache 
especially in case databases fit to shared memory.

Best regards,Alexander Kirpa