Re: I/O and db_file_multiblock_read_count

Adding fuel to the fire.

This on a somewhat busy Dual CPU linux box.
The SAN is Clariion CX700.

Disk is a dedicated RAID10, though I'm not positive about
the number of spindles.  There are I believe 6 spindles.

The command was run once, then both run to account for SAN caching.

time dd if=/u01/oradata/dv04/cimindxsmall_01.dbf of=/dev/null bs=1048576
1500+1 records in
1500+1 records out

real    0m1.207s
user    0m0.002s
sys     0m1.205s

time dd if=/u01/oradata/dv04/cimindxsmall_01.dbf of=/dev/null bs=65536
24000+1 records in
24000+1 records out

real    0m0.744s
user    0m0.014s
sys     0m0.729s

Interesting that the 64K blocksize significantly outperforms the 1M
blocksize.


On 12/11/06, Keith Moore <kmoore@xxxxxxxxxxxx> wrote:


We also use Hitachi Sans. I ran dd for 64K and 1M block sizes and the
reads
with 1M block size were slightly faster. This is on Solaris8 / Sunfire
15K.

Strangely, the sys time is much lower with the 1M blocksize. Is there an
explanation for that?

Keith

orapls> time dd if=polaris_data_04.dbf of=/dev/null bs=65536
163840+1 records in
163840+1 records out

real    4m15.57s
user    0m0.85s
sys     2m37.34s
ddcspora07 - pol2p - /plsoraprd01/u03/oradata/pol2p

orapls> time dd if=polaris_data_04.dbf of=/dev/null bs=1048576
10240+1 records in
10240+1 records out

real    3m59.18s
user    0m0.02s
sys     0m21.93s


> do the "same" thing using dd. Whatever your db_block_size is, plug it in
> as follows:
>
> $ time dd if=<datafile_for_the tablespace> of=-/dev/null
> bs=<block_size_in_bytes*16>
>
> then re-run:
> $ time dd if=<datafile_for_the tablespace> of=-/dev/null
> bs=<block_size_in_bytes*128>
>
> please let me know what you find
>
>
>
>
> ________________________________
>
>       From: oracle-l-bounce@xxxxxxxxxxxxx
> [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Kevin Lidh
>       Sent: Friday, December 08, 2006 12:46 PM
>       To: oracle-l
>       Subject: I/O and db_file_multiblock_read_count
>
>
>       I was reading an article about the appropriate setting for
> db_file_multiblock_read_count.  I'm on a HP-UX 11.11 64-bit system with
> Oracle 9.2.0.7.0.  The original value was 16 and I bounced the database
> and ran a million record full-scan test (10046 trace) and then set the
> value to 128 (max value) and re-ran the
>
>


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Jared Still
Certifiable Oracle DBA and Part Time Perl Evangelist

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