Oracle text performance with context search indexes

Question

Search performance using context index.
We are intending to move our search engine to a new one based on Oracle Text, but we are meeting some
bad performance issues when using search.
Our application allows the user to search stored documents by name, object identifier and annotations(formerly set on objects).
For example, suppose I want to find a document named ImportSax2.c: according to user set parameters, our search engine format the following
search queries :
1) If the user explicitely ask for a search by document name, the query is the following one =>
     select objid FROM ADSOBJ WHERE CONTAINS( OBJFIELDURL , 'ImportSax2.c WITHIN objname' , 1 ) > 0;
2) If the user don't specify any extra parameters, the query is the following one =>
     select objid FROM ADSOBJ WHERE CONTAINS( OBJFIELDURL , 'ImportSax2.c' , 1 ) > 0;
Oracle text only need around 7 seconds to answer the second query, whereas it need around 50 seconds to give an answer for the first query.
Here is a part of the sql script used for creating the Oracle Text index on the column OBJFIELDURL
(this column stores a path to an xml file containing properties that have to be indexed for each object) :
begin
Ctx_Ddl.Create_Preference('wildcard_pref', 'BASIC_WORDLIST');
ctx_ddl.set_attribute('wildcard_pref', 'wildcard_maxterms', 200) ;
ctx_ddl.set_attribute('wildcard_pref','prefix_min_length',3);
ctx_ddl.set_attribute('wildcard_pref','prefix_max_length',6);
ctx_ddl.set_attribute('wildcard_pref','STEMMER','AUTO');
ctx_ddl.set_attribute('wildcard_pref','fuzzy_match','AUTO');
ctx_ddl.set_attribute('wildcard_pref','prefix_index','TRUE');
ctx_ddl.set_attribute('wildcard_pref','substring_index','TRUE');
end;
begin
ctx_ddl.create_preference('doc_lexer_perigee', 'BASIC_LEXER');
ctx_ddl.set_attribute('doc_lexer_perigee', 'printjoins', '_-');
ctx_ddl.set_attribute('doc_lexer_perigee', 'BASE_LETTER', 'YES');
ctx_ddl.set_attribute('doc_lexer_perigee','index_themes','yes');
ctx_ddl.create_preference('english_lexer','basic_lexer');
ctx_ddl.set_attribute('english_lexer','index_themes','yes');
ctx_ddl.set_attribute('english_lexer','theme_language','english');
ctx_ddl.set_attribute('english_lexer', 'printjoins', '_-');
ctx_ddl.set_attribute('english_lexer', 'BASE_LETTER', 'YES');
ctx_ddl.create_preference('german_lexer','basic_lexer');
ctx_ddl.set_attribute('german_lexer','composite','german');
ctx_ddl.set_attribute('german_lexer','alternate_spelling','GERMAN');
ctx_ddl.set_attribute('german_lexer','printjoins', '_-');
ctx_ddl.set_attribute('german_lexer', 'BASE_LETTER', 'YES');
ctx_ddl.set_attribute('german_lexer','NEW_GERMAN_SPELLING','YES');
ctx_ddl.set_attribute('german_lexer','OVERRIDE_BASE_LETTER','TRUE');
ctx_ddl.create_preference('japanese_lexer','JAPANESE_LEXER');
ctx_ddl.create_preference('global_lexer', 'multi_lexer');
ctx_ddl.add_sub_lexer('global_lexer','default','doc_lexer_perigee');
ctx_ddl.add_sub_lexer('global_lexer','german','german_lexer','ger');
ctx_ddl.add_sub_lexer('global_lexer','japanese','japanese_lexer','jpn');
ctx_ddl.add_sub_lexer('global_lexer','english','english_lexer','en');
end;
begin
     ctx_ddl.create_section_group('axmlgroup', 'AUTO_SECTION_GROUP');
end;
drop index ADSOBJ_XOBJFIELDURL force;
create index ADSOBJ_XOBJFIELDURL on ADSOBJ(OBJFIELDURL) indextype is ctxsys.context
parameters
('datastore ctxsys.file_datastore
filter ctxsys.inso_filter
sync (on commit)
lexer global_lexer
language column OBJFIELDURLLANG
charset column OBJFIELDURLCHARSET
format column OBJFIELDURLFORMAT
section group axmlgroup
Wordlist wildcard_pref
Oracle created a table named DR$ADSOBJ_XOBJFIELDURL$I which now contains around 25 millions records.
ADSOBJ is the table contaings information for our documents,OBJFIELDURL is the field that contains the path to the xml file containing
data to index. That file looks like this :
<?xml version="1.0" encoding="UTF-8" ?>
<fields>
<OBJNAME><![CDATA[NomLnk_177527o.jpgp]]></OBJNAME>
<OBJREM><![CDATA[Z_CARACT_141]]></OBJREM>
<OBJID>295926o.jpgp</OBJID>
</fields>
Can someone tell me how I can make that kind of request
"select objid FROM ADSOBJ WHERE CONTAINS( OBJFIELDURL , 'ImportSax2.c WITHIN objname' , 1 ) > 0;"
run faster ?

Answer 1

Below are the execution plan for both the 2 requests :
select objid FROM ADSOBJ WHERE CONTAINS( OBJFIELDURL , 'ImportSax2.c WITHIN objname' , 1 ) > 0
PLAN_TABLE_OUTPUT
|     Id     | Operation                              |Name                         |Rows     |Bytes     |Cost (%CPU)|
|     0     | SELECT STATEMENT                    |                              |1272     |119K     |     4     (0)     |
|     1      | TABLE ACCESS BY INDEX ROWID     |ADSOBJ      |1272     |119K     |     4     (0)     |
|     2      |     DOMAIN INDEX                    |ADSOBJ_XOBJFIELDURL     |          |          |     4     (0)     |
Note
- 'PLAN_TABLE' is old version
Executed in 2 seconds
select objid FROM ADSOBJ WHERE CONTAINS( OBJFIELDURL , 'ImportSax2.c' , 1 ) > 0
PLAN_TABLE_OUTPUT
|     Id     |Operation                              |Name                         |Rows     |Bytes     |Cost (%CPU)|
|     0     | SELECT STATEMENT                    |                              |1272     |119K     |     4     (0)     |
|     1     | TABLE ACCESS BY INDEX ROWID     |ADSOBJ                         |1272     |119K     |     4     (0)     |
|     2     | DOMAIN INDEX                    |ADSOBJ_XOBJFIELDURL     |          |          |     4     (0)     |
Sorry for the result formatting, I can't get it "easily" readable :(