Re: Large discrepancy between 'log file parallel write' and 'db file parallel write' times
From: Tanel Poder <tanel_at_tanelpoder.com>
Date: Sun, 6 Jan 2013 12:43:54 +0800
Message-ID: <CAMHX9JJ2Vb1Z3AFSC1uibK9s4XOqc5UEuZ0HMaW6U_wFJT3zHw_at_mail.gmail.com>
Also note that the "log file parallel write" is not really random IO, compared to a "db file parallel write" which may write hundred(s) of buffers into random locations in a single vector IO call. That makes a difference even on non-exadata without IORM too (especially if there's no write-cache for DBWR writes or the storage array cache destaging can't keep up with the write workload).
Date: Sun, 6 Jan 2013 12:43:54 +0800
Message-ID: <CAMHX9JJ2Vb1Z3AFSC1uibK9s4XOqc5UEuZ0HMaW6U_wFJT3zHw_at_mail.gmail.com>
Also note that the "log file parallel write" is not really random IO, compared to a "db file parallel write" which may write hundred(s) of buffers into random locations in a single vector IO call. That makes a difference even on non-exadata without IORM too (especially if there's no write-cache for DBWR writes or the storage array cache destaging can't keep up with the write workload).
-- Tanel Poder New Online Training! http://blog.tanelpoder.com/seminar On Fri, Jan 4, 2013 at 12:31 AM, John Clarke <john.clarke_at_centroid.com>wrote:Received on Sun Jan 06 2013 - 05:43:54 CET
> The behavior I was describing was specific to IORM & Exadata I/Os. To my
> knowledge there isn't a direct parallel to this for ASM in general, but I'm
> open to be educated ...
> With ASM without Exadata, background I/O is queued according to your async
> I/O configuration (or synchronously depending on O/S and init.ora
> settings), but the operating system or Oracle wouldn't interject any
> prioritization algorithm for LGWR I/Os vs DBWR I/Os.
>
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