ALL_% performance issue in 10G

Question

Hi,
I'm working in 10.2.0.3 and we have a huge difference in performance (compared to Oracle9) whenever we use all_% views.
Any explaination/fix?
Kind Regards,
Ffrank

Answer 1

It is unclear what the purpose or meaning of the copy/paste of the note is.
In 10g, the default value for optimizer_mode has changed. This change requires that statistics be collected the dictionary segments. Examples of these segments are TAB$, OBJ$, SEG$, etc. Statistics on these segments are collected automatically by the 10g maintenance auto stats job (if you haven't disabled it). The V$ and X$ views (these are not physical tables, but rather views into memory structures, but they are called fixed tables) also need statistics collected on them (but just once for a representative workload).
GATHER_FIXED_OBJECTS_STATS collects stats on V$ and X$ fixed tables.
GATHER_DICTIONARY_STATS collects stats on the SYS and SYSTEM segments.
As I mentioned, one needs statistics for both groups.
Given the original post mentioned a large number of objects, chances are the TAB$, SEG$, etc stats are non representative.
I would recommend that you check out
Upgrading from Oracle Database 9i to 10g: What to expect from the Optimizer
http://www.oracle.com/technology/products/bi/db/10g/pdf/twp_bidw_optimizer_10gr2_0208.pdf
This is discussed on page 7 & 8 (Statistics on Dictionary Tables & Statistics on Fixed Objects)
As you can see, ALL_TABLES is composed of fixed tables and sys segments.
SQL> explain plan for select * from all_tables;
Explained.
SQL>  select * from table(dbms_xplan.display(format=>'basic'));
| Id  | Operation                    | Name       |
|   0 | SELECT STATEMENT             |            |
|   1 |  FILTER                      |            |
|   2 |   HASH JOIN RIGHT OUTER      |            |
|   3 |    TABLE ACCESS FULL         | SEG$       |
|   4 |    HASH JOIN RIGHT OUTER     |            |
|   5 |     TABLE ACCESS FULL        | USER$      |
|   6 |     HASH JOIN RIGHT OUTER    |            |
|   7 |      INDEX FAST FULL SCAN    | I_OBJ1     |
|   8 |      HASH JOIN               |            |
|   9 |       TABLE ACCESS FULL      | USER$      |
|  10 |       HASH JOIN              |            |
|  11 |        TABLE ACCESS FULL     | OBJ$       |
|  12 |        HASH JOIN RIGHT OUTER |            |
|  13 |         INDEX FAST FULL SCAN | I_OBJ2     |
|  14 |         HASH JOIN            |            |
|  15 |          MERGE JOIN CARTESIAN|            |
|  16 |           HASH JOIN          |            |
|  17 |            FIXED TABLE FULL  | X$KSPPI    |
|  18 |            FIXED TABLE FULL  | X$KSPPCV   |
|  19 |           BUFFER SORT        |            |
|  20 |            TABLE ACCESS FULL | TS$        |
|  21 |          TABLE ACCESS FULL   | TAB$       |
|  22 |   NESTED LOOPS               |            |
|  23 |    INDEX RANGE SCAN          | I_OBJAUTH1 |
|  24 |    FIXED TABLE FULL          | X$KZSRO    |
|  25 |   FIXED TABLE FULL           | X$KZSPR    |
32 rows selected.--
Regards,
Greg Rahn
http://structureddata.org