Date: Thu, 26 Mar 2009 17:43:10 +1300
From: Mark Kirkwood <markir@paradise.net.nz>
Subject: Re: Raid 10 chunksize
In-reply-to: <49CAD14C.3020507@ummon.com>
To: Stef Telford <stef@ummon.com>
Cc: "pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
Message-id: <49CB07DE.4040102@paradise.net.nz>
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Stef Telford wrote:
>
> Hello Mark,
>     Okay, so, take all of this with a pinch of salt, but, I have the
> same config (pretty much) as you, with checkpoint_Segments raised to
> 192. The 'test' database server is Q8300, 8GB ram, 2 x 7200rpm SATA
> into motherboard which I then lvm stripped together; lvcreate -n
> data_lv -i 2 -I 64 mylv -L 60G (expandable under lvm2). That gives me
> a stripe size of 64. Running pgbench with the same scaling factors;
>
> starting vacuum...end.
> transaction type: TPC-B (sort of)
> scaling factor: 100
> number of clients: 24
> number of transactions per client: 12000
> number of transactions actually processed: 288000/288000
> tps = 1398.907206 (including connections establishing)
> tps = 1399.233785 (excluding connections establishing)
>  
>     It's also running ext4dev, but, this is the 'playground' server,
> not the real iron (And I dread to do that on the real iron). In short,
> I think that chunksize/stripesize is killing you. Personally, I would
> go for 64 or 128 .. that's jst my 2c .. feel free to
> ignore/scorn/laugh as applicable ;)
>
>   
Stef - I suspect that your (quite high) tps is because your SATA disks 
are not honoring the fsync() request for each commit. SCSI/SAS disks 
tend to by default flush their cache at fsync - ATA/SATA tend not to. 
Some filesystems (e.g xfs) will try to work around this with write 
barrier support, but it depends on the disk firmware.

Thanks for your reply!

Mark