Re: Aligning Oracle Blocks with Filesystem Block Size

Hi Richard

Thanks for the reply, I know it has some impact unfortunately this database was created by someone who left the company several monsth ago.

I wonder, why HP is gonna do 2 data block reads? Does it work this way: - Oracle does index range scan and scans 10 blocks, 10 system calls, HP runs 10 systems calls and read 10 8k blocks.
Or how does it work?

By the way I am putting this to Direct I/O soon. Convosync and mincache to direct, I recogn it would achieve some improvements.

TIA Alex

On 11/14/06, Richard J. Goulet <rgoulet_at_kanbay.com> wrote:
>
> Alex
>
>
> Having been a long time HP-UX and OnlineJFS user, your making the
> machine do more work than is needed. Assume that your looking for one row
> of data in one data block. HP is going to read 2 data blocks of data into
> memory for you. The Oracle manuals are pretty good at saying that your
> database block size should be equal to or a multiple of the OS block size.
> BTW: you've also put dbwr into a quagmire at the same time. Since it's
> wetting 4K blocks the OS is going to cache those writes till it gets an 8k
> write to that disk location before it does anything. Now I'm not sure what
> it does in the event that you never write the remaining 4K of data, but I'd
> imagine that it would cache the 4k block in swap for a rather long time.
>
>
>
>
> Dick Goulet, Senior Oracle DBA
>
> 45 Bartlett St Marlborough, Ma 01752, USA
> *Tel.:* 508.573.1978 |F*ax: * 508.229.2019 | Cell:508.742.5795
>
> RGoulet_at_kanbay.com
> : POWERING TRANSFORMATION
>
>
> ------------------------------
> *From:* oracle-l-bounce_at_freelists.org [mailto:
> oracle-l-bounce_at_freelists.org] *On Behalf Of *amonte
> *Sent:* Tuesday, November 14, 2006 9:59 AM
> *To:* oracle-l_at_freelists.org
> *Subject:* Aligning Oracle Blocks with Filesystem Block Size
>
> Hi
>
> I have a 9i database running on HP-UX which uses 4k db_block_size. The
> filesystem used is OnlineJFS (vxfs version 4).
>
> The Filesystem block size is 8k (f_bsize 8192)
>
> I was wondering what sort of impact can this missalignment cause? Would
> I/O system perform twice I/O it should?
>
> TIA
>
> Alex
>
>
>

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