Please see my answers in-line. Guang -----Original Message----- From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx]On Behalf Of Mladen Gogala Sent: Monday, March 01, 2004 12:29 PM To: oracle-l@xxxxxxxxxxxxx Subject: Re: query slow in 9i, but not slow in 8i Are all tables analyzed? Do you have index histograms? Did you collect system statistics? -- all application tables are anaylzed, not sure about index histograms, but don't. -- system statistics: yes -- 9i: SQL> select NAME, Value from v$parameter where name = 'timed_statistics'; NAME ---------------------------------------------------------------- VALUE ---------------------------------------------------------------------------- ---- timed_statistics TRUE -- 8i: MT@atlas-SQL> select NAME, Value from v$parameter where name = 'timed_statistics'; NAME ---------------------------------------------------------------- VALUE ---------------------------------------------------------------------------- ---- timed_statistics TRUE What is are the values of the following parameters: - hash_area_size - hash_join_enabled - optimizer_index_caching - optimizer_index_cost_adj -- 9i: SQL> select NAME, Value from v$parameter where name = 'hash_area_size'; NAME ---------------------------------------------------------------- VALUE ---------------------------------------------------------------------------- ---- hash_area_size 180000000 SQL> select NAME, Value from v$parameter where name = 'hash_join_enabled'; NAME ---------------------------------------------------------------- VALUE ---------------------------------------------------------------------------- ---- hash_join_enabled TRUE SQL> select NAME, Value from v$parameter where name like 'optimizer%'; NAME ---------------------------------------------------------------- VALUE ---------------------------------------------------------------------------- ---- optimizer_features_enable 9.2.0 optimizer_mode CHOOSE optimizer_max_permutations 2000 NAME ---------------------------------------------------------------- VALUE ---------------------------------------------------------------------------- ---- optimizer_index_cost_adj 100 optimizer_index_caching 0 optimizer_dynamic_sampling 1 -- 8i: MT@atlas-SQL> select NAME, Value from v$parameter where name = 'hash_area_size'; NAME ---------------------------------------------------------------- VALUE ---------------------------------------------------------------------------- ---- hash_area_size 180000000 MT@atlas-SQL> select NAME, Value from v$parameter where name = 'hash_join_enabled'; NAME ---------------------------------------------------------------- VALUE ---------------------------------------------------------------------------- ---- hash_join_enabled TRUE MT@atlas-SQL> select NAME, Value from v$parameter where name like 'optimizer%'; NAME ---------------------------------------------------------------- VALUE ---------------------------------------------------------------------------- ---- optimizer_features_enable 8.1.7 optimizer_mode CHOOSE optimizer_max_permutations 80000 NAME ---------------------------------------------------------------- VALUE ---------------------------------------------------------------------------- ---- optimizer_index_cost_adj 100 optimizer_index_caching 0 optimizer_percent_parallel 0 On 03/01/2004 12:09:48 PM, Guang Mei wrote: > 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 -----------------------------------------------------------------