Re: iostat - multiblock read count

utkanbir wrote:
> Hi ,
>
> My system is a two node rac on redhat linux 2.1 , 4 ia64 cpus ,
> 8gb.ram , ocfs and emc raid 10
>
> The db_block_size is 16kb. , current multi_block_read_Count is 64
> (which makes 1mb. of read)
>
>
> Below is some samples for different multiblock read counts . It seems
> when i decrease the multblock read count , performance increases:
>
> Sample query :
>
> select /*+parallel(m,8)*/count(*) from taniadm.MERKEZ_CIKIS_34 m
>
> the table is stored in a tablespace within locally managed tablespace
> . The tablespace uses uniform extent sizes of 10mb. ( I have just
> created it for this test, and have chosen this large extent size in
> order to allow dbserver to use multiblock effectively.)
>
>
>
> parallel 8 , 64 multiblock takes : 1:07 min.
>
> Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await
> svctm %util
> sdh1 43890.20 0.00 896.80 1.40 50860.00 1.40 56.63 119.07 131.83 1.09
> 100.00
>
> parallel 8 , 32 multiblock takes : 59 sec
>
> Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await
> svctm %util
> sdh1 56885.00 0.00 1051.60 1.20 58651.60 1.20 55.71 138.40 130.24 0.93
> 100.00
>
> parallel 8 , 16 multiblock takes : 45 secs
>
> Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await
> svctm %util
> sdh1 66734.20 0.00 1347.80 1.80 76781.60 1.80 56.89 48.62 36.00 0.72
> 100.00
>
> parallel 8 , 8 multiblcok takes: 44 sec
>
> Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await
> svctm %util
> sdh1 66598.40 0.00 1371.40 2.00 77467.20 2.00 56.41 24.22 17.66 0.71
> 100.02
>
>
> 1.It seems when i decrease the multiblock read count parameter , the
> rsec/s increases , but i expect to see the opposite.What's wrong with
> this?
>
> 2. Are the values in r/s normal? Or do they point that my disks are
> saturated. I have read an article explaining that 100 or 200 read per
> second is enough to saturate disks but here i see large values .
>
> 3. Related to my second question , since i use raid 10 (striping +
> mirroring ) is it possible to get higher io rates ? Looking at the
> iostat values , (rsec/s) / (r/s) more or less equals to 28kb. (This is
> the kb. read in each read.)It seems a very low value to me. On a sun
> solaris ufs file system for instance , i can achive 128KB or even 1MB.
> per read by playing with the parameters , i dont understand why my
> linux box is different.
>
>
> Any help will be appreciated.
> Kind Regards,
> tolga

To answer your questions really requires a StatsPack or AWR Report

Upgrading to RedHat 3 will likely improve things substantially

Depending on your hardware you could look at ethernet bonding to increase through-put. Depends on what the limiting factor is.

-- 
Daniel A. Morgan
http://www.psoug.org
damorgan_at_x.washington.edu
(replace x with u to respond)