Re: PostgreSQL on 64 bit Linux

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

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