"Brian C. Doyle" wrote:
> Another thing to rember about PostgreSQL is DB Size vs CPU bits
> Performance of 32-bit cpu machines will decline rapidly when the
> database size exceeds 5 GigaByte. You can run 30 gig database on
> 32-bit cpu but the performance will be degraded. Machines with 32-bit
> cpu imposes a limitation of 2 GB on RAM, 2 GB on file system sizes and
> other limitations on the operating system. Use the special filesystems
> for linux made by SGI, IBM or HP or ext3-fs to support file-sizes
> greater than 2 GB on 32-bit linux machines.
> found at http://www.linuxdoc.org/HOWTO/PostgreSQL-HOWTO-8.html
I would take anything found in that document with a grain or barrel of
salt. (Read chapter 2 of it for a taste of it unsalted....)
Above a certain configurable size (correct me if I am wrong, but I think
it is currently 1GB), tables are segmented in PostgreSQL. The more
segments, the more likely you might take a performance hit.
But the CPU bittedness is not the real limit for large tables, thanks to
the automatic segmentation -- hard disk transfer rates and seek times
are. Of course, the more RAM you can throw at it, the better -- but
that is true with any CPU, not just 32 bit ones.
But of course you do have real limits for 32-bit addressing CPU's (a 32
bit CPU is not necessarily limited to 32 address bus bits -- the
bittedness of the CPU is basic register word size, not dependent upon
bus size (8088, with an 8 bit data bus, a 20 bit address bus, and 16 bit
register word size, is a 16 bit cpu, for instance -- the 80386SX, with a
16 bit data bus, a 32 bit address bus (well, in all technicality, IIRC
it's a 31 bit address bus with a high-byte/low-byte/full word control
implementation -- ie, it addresses 32 bits for byte addressing, not word
addressing) was a 32 bit CPU -- and the original 68000 with a 16 bit
data bus and a 24 bit address bus was, in the register sense, a 32 bit
CPU). The physical RAM is limited by physical address bus size -- on
the ia32 architecture that is 4 GB, IIRC.
A 64 bit CPU with a 32 bit address bus is still limited to 4 gigawords
(32 GB) physical RAM.
RAM size has everything to do with the address bus size -- but file size
has to do with basic data representation, typically limited by the
register size of the CPU.
The 2GB size limits of ia32 come in to play due to byte addressing
(versus word addressing) in ia32 plus the use of signed single register
two's-complement integers.
But, as always, I reserve the right to be wrong.
--
Lamar Owen
WGCR Internet Radio
1 Peter 4:11
