Re: Too many db calls

Cary,

Thank you.

Could you elaborate on the issue of excessive database calls, which show up as excessive network traffic?

I can picture a PL/SQL loop, which executes an SQL statement over and over again. This would produce many database calls, and it might be possible to remove the loop altogether, replacing it with a single SQL statement. This would reduce the database calls.

Is this the "classic" type of situation that produces too many db calls? Or are there other situations I'm missing that are more likely to be the source of this problem?

Thanks again.

• Original Message ----- To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com> Sent: Friday, November 15, 2002 4:13 PM

> Greg,
>
> I believe that the cultural root cause of the excessive LIO problem is
> the conception that physical I/O is what makes databases slow. Disk I/O
> certainly *can* make a system slow, but in about 598 of 600 cases we've
> seen in the past three years, it hasn't. ["Why you should focus on LIOs
> instead of PIOs" at www.hotsos.com/catalog]
>
> The fixation on PIO of course focuses people's attention on the database
> buffer cache hit ratio (BCHR) metric for evaluating efficiency. The
> problem is that the BCHR is a metric of INSTANCE efficiency, not SQL
> efficiency. However, many people mistakenly apply it as a metric of SQL
> efficiency anyway.
>
> Of course, if one's radar equates SQL efficiency with the BCHR's
> proximity to 100%, then a lot of really bad SQL is going to show up on
> your radar wrongly identified as really good SQL. ["Why a 99% buffer
> cache hit ratio is not okay" at www.hotsos.com/catalog]
>
> One "classic" result is that people go on search and destroy missions
> for all full-table scans. They end up producing more execution plans
> that look like this than they should have:
>
> NESTED LOOPS
> TABLE ACCESS BY INDEX ROWID
> INDEX RANGE SCAN
> TABLE ACCESS BY INDEX ROWID
> INDEX RANGE SCAN
>
> This kind of plan produces great hit ratios because it tends to revisit
> the same small set of blocks over and over again. This kind of plan is
> of course appropriate in many cases. But sometimes it is actually less
> work in the database to use full-table scans. ["When to use an index" at
> www.hotsos.com/catalog.]
>
>
> Cary Millsap
> Hotsos Enterprises, Ltd.
> http://www.hotsos.com
>
> Upcoming events:
> - Hotsos Clinic, Dec 9-11 Honolulu
> - 2003 Hotsos Symposium on OracleR System Performance, Feb 9-12 Dallas
> - Jonathan Lewis' Optimising Oracle, Nov 19-21 Dallas
>
>
> -----Original Message-----
> Sent: Friday, November 15, 2002 4:39 PM
> To: Multiple recipients of list ORACLE-L
>
> A while back someone mentioned that the two main causes of slow SQL are
> excesive LIO's and excesscive database calls, which show up as excessive
> CPU
> use and excessive network traffic, respectively.
>
> Regarding the database calls, is there a "classic" reason for this
> problem?
>
> My best guess is it's caused by an SQL statement in a PL/SQL loop, which
> could be rewritten as a single SQL statement. But is this the single,
> commonly seen cause for this problem, or are there other common ways
> this
> inefficiency is introduced?
>
> Thanks in advance for help in understanding this.
>
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.com
> --
> Author: Greg Moore
> INET: sqlgreg_at_pacbell.net
>
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-- 
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-- 
Author: Greg Moore
  INET: sqlgreg_at_pacbell.net

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