Disappointing query performance with object-relational storag

Question

Hello,
after some frustrating days trying to improve query performance on an xmltype table I'm on my wits' end. I have tried all possible combinations of indexes, added scopes, tried out of line and inline storage, removed recursive type definition from the schema, tried the examples from the form thread Setting Attribute SQLInline to false for Out-of-Line Storage (having the same problems) and still have no clue. I have prepared a stripped down example of my schema which shows the same problems as the real one. I'm using 10.2.0.4.0:
SQL> select * from v$version;
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - Prod
PL/SQL Release 10.2.0.4.0 - Production
CORE 10.2.0.4.0 Production
TNS for Linux: Version 10.2.0.4.0 - Production
NLSRTL Version 10.2.0.4.0 - Production
You can find the script on http://www.grmblfrz.de/xmldbproblem.sql (I tried including it here but got an internal server error) The results are on http://www.grmblfrz.de/xmldbtest.lst . I have no idea how to improve the performance (and if even with this simple schema query rewrite does not work, how can oracle xmldb be feasible for more complex structures?). I must have made a mistake somewhere, hopefully someone can spot it.
Thanks in advance.
--Swen
Edited by: user636644 on Aug 30, 2008 3:55 PM
Edited by: user636644 on Aug 30, 2008 4:12 PM

Answer 1

Marc,
thanks, I did not know that it is possible to use "varray store as table" for the reference tables. I have tried your example. I can create the nested table, the scope and the indexes, but I get a different result - full table scan on t_element. With the original table I get an index scan. On the original table there is a trigger (t_element$xd) which is missing on the new table. I have tried the same with an xmltype table (drop table t_element; create table t_element of xmltype ...) with the same result. My script ... is on [google groups|http://groups.google.com/group/oracle-xmldb-temporary-group/browse_thread/thread/f30c3cf0f3dbcafc] (internal server error while trying to include it here). Here is the plan of the query
select rt.object_value
from t_element rt
where existsnode(rt.object_value,'/mddbelement/group[attribute[@name="an27"]="99"]') = 1;
Execution Plan
Plan hash value: 4104484998
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
| 0 | SELECT STATEMENT | | 1 | 40 | 2505 (1)| 00:00:38 |
| 1 | TABLE ACCESS BY INDEX ROWID | NT_GROUP | 1 | 20 | 3 (0)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | SYS_C0082879 | 1 | | 2 (0)| 00:00:01 |
|* 3 | FILTER | | | | | |
| 4 | TABLE ACCESS FULL | T_ELEMENT | 1000 | 40000 | 4 (0)| 00:00:01 |
| 5 | NESTED LOOPS SEMI | | 1 | 88 | 5 (0)| 00:00:01 |
| 6 | NESTED LOOPS | | 1 | 59 | 4 (0)| 00:00:01 |
| 7 | TABLE ACCESS BY INDEX ROWID| NT_GROUP | 1 | 20 | 3 (0)| 00:00:01 |
|* 8 | INDEX RANGE SCAN | SYS_C0082879 | 1 | | 2 (0)| 00:00:01 |
|* 9 | TABLE ACCESS BY INDEX ROWID| T_GROUP | 1 | 39 | 1 (0)| 00:00:01 |
|* 10 | INDEX UNIQUE SCAN | SYS_C0082878 | 1 | | 0 (0)| 00:00:01 |
|* 11 | INDEX RANGE SCAN | SYS_IOT_TOP_184789 | 1 | 29 | 1 (0)| 00:00:01 |
Predicate Information (identified by operation id):
2 - access("NESTED_TABLE_ID"=:B1)
3 - filter( EXISTS (SELECT /*+ ???)
8 - access("NESTED_TABLE_ID"=:B1)
9 - filter("T_GROUP"."SYS_NC0001300014$" IS NOT NULL AND
SYS_CHECKACL("ACLOID","OWNERID",xmltype('<privilege
xmlns="http://xmlns.oracle.com/xdb/acl.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-insta
nce" xsi:schemaLocation="http://xmlns.oracle.com/xdb/acl.xsd
http://xmlns.oracle.com/xdb/acl.xsd DAV:http://xmlns.oracle.com/xdb/dav.xsd"><read-properties
/><read-contents/></privilege>'))=1)
10 - access("SYS_ALIAS_3"."COLUMN_VALUE"="T_GROUP"."SYS_NC_OID$")
11 - access("NESTED_TABLE_ID"="T_GROUP"."SYS_NC0001300014$")
filter("SYS_XDBBODY$"='99' AND "NAME"='an27')
Edited by: user636644 on Sep 1, 2008 9:56 PM