> 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.

Best regards,
 Alexander Kirpa

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