Re: dbt2 NOTPM numbers

Hi,

PFC wrote:
> You have a huge amount of iowait !

Yup.

> Did you put the xlog on a separate disk ?

No, it's all one big RAID6 for the sake of simplicity (plus I doubt
somewhat, that 2 disks for WAL + 5 for data + 1 spare would be much
faster than 7 disks for WAL and data + 1 spare - considering that RAID6
needs two parity disks, that's 3 vs 5 disks for data...)

> What filesystem do you use ?

XFS

> Did you check that your BBU cache works ?

Thanks to you're hint, yes. I've attached the small python script, in
case it might help someone else, too.

> For that run a dumb script which does INSERTS in a test table in
> autocommit mode ; if you get (7200rpm / 60) = 120 inserts / sec or less,
> the good news is that your drives don't lie about fsync, the bad news is
> that your BBU cache isn't working...

According to my little script, I constantly get somewhat around 6000
inserts per second, so I guess either my BBU works, or the drives are
lying ;-) Simplistic troughput testing with dd gives > 200MB/s, which
also seems fine.

Obviously there's something else I'm doing wrong. I didn't really care
much about postgresql.conf, except setting a larger shared_buffers and a
reasonable effective_cache_size.

Oh, something else that's probably worth thinking about (and just came
to my mind again): the XFS is on a lvm2, on that RAID6.

Regards

Markus

Simplistic throughput testing with dd:

dd of=test if=/dev/zero bs=10K count=800000
800000+0 records in
800000+0 records out
8192000000 bytes (8.2 GB) copied, 37.3552 seconds, 219 MB/s
pamonth:/opt/dbt2/bb# dd if=test of=/dev/zero bs=10K count=800000
800000+0 records in
800000+0 records out
8192000000 bytes (8.2 GB) copied, 27.6856 seconds, 296 MB/s