Re: Performance PG 8.0 on dual opteron / 4GB / 3ware Raid5 / Debian??

Where are the pg_xlog and data directories with respect to each other?
From this IOStat it looks like they might be on the same partition,
which is not ideal, and actualy surprising that throughput is this
good. You need to seperate pg_xlog and data directories to get any
kind of reasonable performance. Also don't use RAID 5 - RAID 5 bites,
no really - it bites. Use multiple RAID 1s, or RAID 10s, you will get
better performance. 50MB/70MB is about the same as you get from a
single disk or a RAID 1.

We use 2x9506S8MI controlers, and have maintained excellent
performance with 2xRAID 10 and 2xRAID 1. Make sure you get the
firmware update if you have these controllers though.

Alex Turner
NetEconomist

On 11/6/05, Joost Kraaijeveld <J(dot)Kraaijeveld(at)askesis(dot)nl> wrote:
> Hi,
>
> I am experiencing very long update queries and I want to know if it
> reasonable to expect them to perform better.
>
> The query below is running for more than 1.5 hours (5500 seconds) now,
> while the rest of the system does nothing (I don't even type or move a
> mouse...).
>
> - Is that to be expected?
> - Is 180-200 tps with ~ 9000 KB (see output iostat below) not low, given
> the fact that fsync is off? (Note: with bonnie++ I get write
> performance > 50 MB/sec and read performace > 70 MB/sec with > 2000
> read/write ops /sec?
> - Does anyone else have any experience with the 3Ware RAID controller
> (which is my suspect)?
> - Any good idea how to determine the real botleneck if this is not the
> performance I can expect?
>
> My hard- and software:
>
> - PostgreSQL 8.0.3
> - Debian 3.1 (Sarge) AMD64
> - Dual Opteron
> - 4GB RAM
> - 3ware Raid5 with 5 disks
>
> Pieces of my postgresql.conf (All other is default):
> shared_buffers = 7500
> work_mem = 260096
> fsync=false
> effective_cache_size = 32768
>
>
>
> The query with explain (amount and orderbedrag_valuta are float8,
> ordernummer and ordernumber int4):
>
> explain update prototype.orders set amount =
> odbc.orders.orderbedrag_valuta from odbc.orders where ordernumber =
> odbc.orders.ordernummer;
> QUERY PLAN
> -----------------------------------------------------------------------------
> Hash Join (cost=50994.74..230038.17 rows=1104379 width=466)
> Hash Cond: ("outer".ordernumber = "inner".ordernummer)
> -> Seq Scan on orders (cost=0.00..105360.68 rows=3991868 width=455)
> -> Hash (cost=48233.79..48233.79 rows=1104379 width=15)
> -> Seq Scan on orders (cost=0.00..48233.79 rows=1104379
> width=15)
>
>
> Sample output from iostat during query (about avarage):
> Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
> hdc 0.00 0.00 0.00 0 0
> sda 0.00 0.00 0.00 0 0
> sdb 187.13 23.76 8764.36 24 8852
>
>
> --
> Groeten,
>
> Joost Kraaijeveld
> Askesis B.V.
> Molukkenstraat 14
> 6524NB Nijmegen
> tel: 024-3888063 / 06-51855277
> fax: 024-3608416
> e-mail: J(dot)Kraaijeveld(at)Askesis(dot)nl
> web: www.askesis.nl
>
>
>
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