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. ----- Original Message ----- From: "Guang Mei" <gmei@xxxxxxxxxx> To: "Oracle-L-freelists" <oracle-l@xxxxxxxxxxxxx> Sent: Monday, March 01, 2004 1:09 PM Subject: query slow in 9i, but not slow in 8i > 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 > > > > ---------------------------------------------------------------- > Please see the official ORACLE-L FAQ: http://www.orafaq.com > ---------------------------------------------------------------- > To unsubscribe send email to: oracle-l-request@xxxxxxxxxxxxx > put 'unsubscribe' in the subject line. > -- > Archives are at //www.freelists.org/archives/oracle-l/ > FAQ is at //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@xxxxxxxxxxxxx put 'unsubscribe' in the subject line. -- Archives are at //www.freelists.org/archives/oracle-l/ FAQ is at //www.freelists.org/help/fom-serve/cache/1.html -----------------------------------------------------------------