Hardware suggestions for Linux/PGSQL server - Mailing list pgsql-performance

Hi everyone,

I want to pick your brains for hardware suggestions about a
Linux-based PostgreSQL 7.4 server.  It will be a dedicated DB server
backing our web sites and hit by application servers (which do
connection pooling).  I've hopefully provided all relevant
information below.  Any thoughts, comments or suggestions are welcome.

Our current server and database:
    Mac OS X Server 10.2.8
    single 1.25GHz G4
    2 GB 333MHz RAM
    7200 rpm SCSI drive for OS, logs
    15k rpm SCSI drive for data

    PostgreSQL 7.3.4
    1 database, 1.1 GB in size, growing by ~15 MB / week
    60 tables, 1 schema, largest is 1m rows, 1 at 600k, 3 at 100k
    Peak traffic:
        500 UPDATEs, INSERTs and DELETEs / minute
        6000 SELECTs / minutes
        90 connections

Performance is fine most of the time, but not during peak loads.
We're never swapping and disk IO during the SELECT peaks is hardly
anything (under 3MB/sec).  I think UPDATE peaks might be saturating
disk IO.  Normally, most queries finish in under .05 seconds.  Some
take 2-3 seconds.  During peaks, the fast queries are just OK and the
slower ones take too long (like over 8 seconds).

We're moving to Linux from OS X for improved stability and more
hardware options.  We need to do this soon.  The current server is
max'd out at 2GB RAM and I'm afraid might start swapping in a month.

Projected database/traffic in 12 months:
    Database size will be at least 2.5 GB
    Largest table still 1m rows, but 100k tables will grow to 250k
    Will be replicated to a suitable standby slave machine
    Peak traffic:
        2k UPDATEs, INSERTs, DELETEs / minute
        20k SELECTs / minute
        150 - 200 connections

We're willing to shell out extra bucks to get something that will
undoubtedly handle the projected peak load in 12 months with
excellent performance.  But we're not familiar with PG's performance
on Linux and don't like to waste money.

I've been thinking of this (overkill? not enough?):
    2 Intel 32-bit CPUs
    Lowest clock speed chip for the fastest available memory bus
    4 GB RAM (maybe we only need 3 GB to start with?)
    SCSI RAID 1 for OS
    For PostgreSQL data and logs ...
        15k rpm SCSI disks
        RAID 5, 7 disks, 256MB battery-backed write cache
        (Should we save $ and get a 4-disk RAID 10 array?)

I wonder about the 32bit+bigmem vs. 64bit question.  At what database
size will we need more than 4GB RAM?

We'd like to always have enough RAM to cache the entire database.
While 64bit is in our long-term future, we're willing to stick with
32bit Linux until 64bit Linux on Itanium/Opteron and 64bit PostgreSQL
"settle in" to proven production-quality.

TIA,
- Jeff

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Jeff Bohmer
VisionLink, Inc.
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303.402.0170
www.visionlink.org
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