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Home -> Community -> Mailing Lists -> Oracle-L -> RE: query slow in 9i, but not slow in 8i
Yes, The statistics is update to date on all the tables (in both 8i and 9i).
I ran
execute DBMS_STATS.GATHER_TABLE_STATS(<owenr>, <table_name> ,cascade => TRUE); on all the tables in the schema.
Guang
-----Original Message-----
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org]On Behalf Of Juan Cachito Reyes
Pacheco
Sent: Monday, March 01, 2004 12:11 PM
To: oracle-l_at_freelists.org
Subject: Re: query slow in 9i, but not slow in 8i
If you have statictis up to date with dbms package.
We had a problem with the new views cbo feature
try to use the /*+ NO_MERGE */ hint,
if this is the same problem we had , this will fix that.
Otherwise no idea.
> Hi:
>
> I have a query which gave two very different explain plan on 8173 and
9204.
> The two instances (on two separate Sun Solaris boxes) both have the same
> db_file_multiblock_read_count (8), block_size (8k), sort_area_size
> (90000000) and sort_area_retained_size (9000000). I narrowed down the part
> which causeed this:
>
> select distinct accession2, id from (
> select accession2,
> Identifier.id
> from mt.External_accession, mt.identifier
> where external_accession.SEQTABLEID = identifier.seqtabid and
> identifier.type != 'A' and
> identifier.speciesid in
> (24,31,2,19,18,17,23,21,27,32,20,34,30,22,25,26,28,29)
> );
>
>
> -- on 9204 (slow):
>
> Execution Plan
> ----------------------------------------------------------
> 0 SELECT STATEMENT Optimizer=CHOOSE (Cost=118228 Card=8046044
> Bytes=225289232)
>
> 1 0 SORT (UNIQUE) (Cost=118228 Card=8046044 Bytes=225289232)
> 2 1 MERGE JOIN (Cost=1102 Card=8046044 Bytes=225289232)
> 3 2 TABLE ACCESS (BY INDEX ROWID) OF 'EXTERNAL_ACCESSION'
> (Cost=826 Card=28898835 Bytes=404583690)
>
> 4 3 INDEX (FULL SCAN) OF 'EXTACC_SEQTABID_INDEX' (NON-UN
> IQUE) (Cost=26 Card=28898835)
>
> 5 2 SORT (JOIN) (Cost=276 Card=51045 Bytes=714630)
> 6 5 TABLE ACCESS (FULL) OF 'IDENTIFIER' (Cost=96 Card=51
> 045 Bytes=714630)
>
>
> -- on 8173 (not slow):
>
> Execution Plan
> ----------------------------------------------------------
> 0 SELECT STATEMENT Optimizer=CHOOSE (Cost=77324 Card=6490972 B
> ytes=188238188)
>
> 1 0 SORT (UNIQUE) (Cost=77324 Card=6490972 Bytes=188238188)
> 2 1 HASH JOIN (Cost=41347 Card=6490972 Bytes=188238188)
> 3 2 TABLE ACCESS (FULL) OF 'IDENTIFIER' (Cost=95 Card=3892
> 9 Bytes=545006)
>
> 4 2 TABLE ACCESS (FULL) OF 'EXTERNAL_ACCESSION' (Cost=4111
> 4 Card=38102138 Bytes=571532070)
>
>
> It looks like 9i thinks MERGE JOIN is better than HASH JOIN for the
subquery
> (which is fine). The problem is that when I have "select distinct
> accession2, id from ..." from the outside, the "SORT (UNIQUE)" part makes
> the cost 100 times higher in 9204 (from 1102 to 118228) while in 8173 it
> only increases the cost less than two times (from 41347 to 77324).
>
> I tried the a couple of ways in 9i, such as adding a hint /*+
> USE_HASH(identifier) */ in the subquery. This did results in the subquery
> using hash join instead of merge join, but it did not solve the problem.
The
> cost still went to 100 times higher when I put "select distinct
accession2,
> id from ..." there. I aslo changed the init parameter
> "optimizer_max_permutations" to 80000 for the session but it did not help
> either.
>
> So my question is:
>
> 1. What is the reason that in 9204 the sort opration costs that high while
> it does not in 8173?
>
> 2. Any work around?
>
> TIA.
>
> Guang
>
>
>
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-- Archives are at http://www.freelists.org/archives/oracle-l/ FAQ is at http://www.freelists.org/help/fom-serve/cache/1.html ----------------------------------------------------------------- ---------------------------------------------------------------- Please see the official ORACLE-L FAQ: http://www.orafaq.com ---------------------------------------------------------------- To unsubscribe send email to: oracle-l-request_at_freelists.org put 'unsubscribe' in the subject line. -- Archives are at http://www.freelists.org/archives/oracle-l/ FAQ is at http://www.freelists.org/help/fom-serve/cache/1.html -----------------------------------------------------------------Received on Mon Mar 01 2004 - 11:18:38 CST
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