IDS Forum

RE: RE: BUFFERPOOL

Posted By: Mike Walker
Date: Thursday, 1 February 2018, at 8:23 a.m.

In Response To: Re: RE: BUFFERPOOL (MUKESH TANUKU)

Those values are high - indicating that the contents of the bufferpools are
being overwritten frequently. The lower the number the better, and below 10
is a good value to aim for.

Are you actually experiencing any performance problems, or is this more of
an academic exercise?

From these numbers, I would suggest increasing the size of both bufferpools
(maybe doubling if you can), and then checking the BTR again after the
system has been up for a while to see if it has improved.

You must also undertake some tuning of the queries, focusing on which ones
are reading more records than are actually needed. The tuning can get quite
involved, but a good place to start is to look for full table scans of large
tables. A scan of a big table can overwrite everything in the bufferpool.
If you have frequent scans of the same table (assuming that it doesn't all
fit in the bufferpool), or scans of multiple tables, then this can easily
result in the bufferpool contents continually being overwritten - resulting
in poor caching.

Here's a query that I use to identify the 5 tables with the highest KB
scanned per hour. It might be a good start to find out which tables may be
responsible for overwriting the cache:

select first 5

p.dbsname, p.tabname,

p.seqscans,

i.ti_nrows,

round((i.ti_npused * i.ti_pagesize/1024),0) size_kb,

round(p.seqscans /

(select (((sh_curtime - sh_pfclrtime)/60)/60)

from sysshmvals),0) scans_hr,

round(p.seqscans * i.ti_nrows /

(select (((sh_curtime - sh_pfclrtime)/60)/60)

from sysshmvals),0) rows_scn_hr,

round(p.seqscans * (i.ti_npused * i.ti_pagesize/1024) /

(select (((sh_curtime - sh_pfclrtime)/60)/60)

from sysshmvals),0) kb_scn_hr,

dbinfo("DBSPACE", partnum) dbspace,

(select ROUND ((((sh_curtime - sh_pfclrtime)/60)/60),2)

from sysshmvals) hr_since_reset
from sysptprof p, systabinfo i
where p.partnum = i.ti_partnum
order by kb_scn_hr desc;

Once you identify these, you will need to look at the queries that are
running against these tables to see which ones can be tuned.

You may also want to start by looking at the queries that are simply taking
a long time to complete, or doing many reads/writes. You can monitor with
onstats (-u, -g ntt, -ses), or try using SQLTRACE to capture them.

Mike Walker
Advanced DataTools Corporation

-----Original Message-----
From: ids-bounces@iiug.org [mailto:ids-bounces@iiug.org] On Behalf Of MUKESH
TANUKU
Sent: Thursday, February 01, 2018 1:58 AM
To: ids@iiug.org
Subject: Re: RE: BUFFERPOOL [40619]

Hello Mike

I got the BTR for my database.

bufsize pagreads bufwrites nbuffs btr
------- ----------- ----------- ------ ----
4096 13085208125 14482959 126057 427.6493472
8192 812811552 21356077543 224950 405.5567738

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Messages In This Thread

• BUFFERPOOL
  MUKESH TANUKU -- Wednesday, 31 January 2018, at 12:51 p.m.
  • Re: BUFFERPOOL
    MUKESH TANUKU -- Wednesday, 31 January 2018, at 1:04 p.m.
    • Re: BUFFERPOOL
      Jack Parker -- Wednesday, 31 January 2018, at 1:31 p.m.
  • RE: BUFFERPOOL
    Mike Walker -- Wednesday, 31 January 2018, at 1:05 p.m.
    • Re: RE: BUFFERPOOL
      MUKESH TANUKU -- Thursday, 1 February 2018, at 3:57 a.m.
      • RE: RE: BUFFERPOOL
        Mike Walker -- Thursday, 1 February 2018, at 8:23 a.m.
        • RE: RE: BUFFERPOOL
          Mike Walker -- Thursday, 1 February 2018, at 8:27 a.m.
          • Re: RE: RE: BUFFERPOOL
            MUKESH TANUKU -- Friday, 2 February 2018, at 2:43 a.m.
        • Re: RE: RE: BUFFERPOOL
          MUKESH TANUKU -- Friday, 9 February 2018, at 7:01 a.m.
          • RE: RE: RE: BUFFERPOOL
            Mike Walker -- Friday, 9 February 2018, at 8:15 a.m.
            • Re: RE: RE: RE: BUFFERPOOL
              MUKESH TANUKU -- Saturday, 10 February 2018, at 12:51 a.m.
              • RE: RE: RE: RE: BUFFERPOOL
                Mike Walker -- Saturday, 10 February 2018, at 9:54 a.m.

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