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Re: Database link. Select performance mystery

From: Alexander Zemerov <azemerov_at_yahoo.com>
Date: 22 Nov 2002 14:55:33 -0800
Message-ID: <3ba925c8.0211221455.3c980d0@posting.google.com>


How could network problem influence query performance differently for two tables located on the same schema?

Sybrand Bakker <gooiditweg_at_sybrandb.demon.nl> wrote in message news:<q4hqtuogl56v6qufvdg87eov02as4ntum4_at_4ax.com>...
> On 21 Nov 2002 12:25:44 -0800, azemerov_at_yahoo.com (Alexander Zemerov)
> wrote:
>
> >Hi,
> >
> >I found that select query performance through database link has very
> >unpredictabale dependency on the source table, source and destination
> >databases.
> >
> >I have three different schemas on three different instances -
> >SRC_at_SRCDB, DST_at_DSTDB1 and DST_at_DSTDB2. SRC schema contains two table
> >TABLE1 and TABLE2, tables have different structures. DST_at_DSTDB1 and
> >DST_at_DB2 schemas have database links to the SRC_at_SRCDB named SRCDB.
> >I execute the next script on these three schemas. In case of SRC
> >schema I used simple table names without database link name becouse I
> >select the local tables. Additionally I used different ROWNUM limits
> >to get acceptable responce time in case of slow performance on the
> >DSTDB2.

...
> > from from from
> >table SRC (locally) DSTDB1 DSTDB2
> > about the same about the same very different!!!!
> >------- -------------- -------------- ------------
> >TABLE1 100,000/5=20000 100,000/20=500 1,000/70= 14
> >TABLE2 100,000/4=25000 100,000/12=833 10,000/5=2000
> >
> >My question is
> >Why select performance for TABLE1 and TABLE2 from the DSTDB1 is about
> >the same (500 ws 833), but from the DSTDB2 the results are so
> >drammatically different ( 14 ws 2000)? I can not find any reasonable
> >explanation.
> >
> >Thanks for any idea.
> >Alexander.
>
>
> Obviously you need first to exclude it's a network problem.
>
> Hth
>
>
> Sybrand Bakker, Senior Oracle DBA
>
> To reply remove -verwijderdit from my e-mail address
Received on Fri Nov 22 2002 - 16:55:33 CST

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