Viewing Execution Plans

You can generate and view execution plans for queries against cubes and dimensions the same as for those against relational tables.

The SQL EXPLAIN PLAN command creates a table with the content of the explain plan. The default table name is PLAN_TABLE.

Generating Execution Plans

The following command creates an execution plan for a basic query on a cube:

EXPLAIN PLAN FOR
  SELECT t.long_description time,
     p.long_description product,
     cu.long_description customer,
     ch.long_description channel,
     f.sales sales
  FROM time_calendar_view t,
     product_primary_view p,
     customer_shipments_view cu,
     channel_primary_view ch,
     units_cube_view f
  WHERE t.level_name = 'CALENDAR_YEAR'
     AND p.level_name = 'TOTAL'
     AND cu.level_name = 'TOTAL'
     AND ch.level_name = 'TOTAL'
     AND t.dim_key = f.TIME
     AND p.dim_key = f.product
     AND cu.dim_key = f.customer
     AND ch.dim_key = f.channel
  ORDER BY t.end_date;

The DISPLAY table function of the DBMS_XPLAN PL/SQL package formats and displays information from an execution plan, as shown in Example: Execution Plan for a Cube Query.

Example 3-8 Execution Plan for a Cube Query

SQL> SELECT plan_table_output FROM TABLE(dbms_xplan.display());
 
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------
Plan hash value: 1667678335
 
----------------------------------------------------------------------------------------------
| Id  | Operation                       | Name       | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                |            |     1 |   100 |   104   (3)| 00:00:02 |
|   1 |  SORT ORDER BY                  |            |     1 |   100 |   104   (3)| 00:00:02 |
|   2 |   JOINED CUBE SCAN PARTIAL OUTER|            |       |       |            |          |
|   3 |    CUBE ACCESS                  | UNITS_CUBE |       |       |            |          |
|   4 |    CUBE ACCESS                  | CHANNEL    |       |       |            |          |
|   5 |    CUBE ACCESS                  | CUSTOMER   |       |       |            |          |
|   6 |    CUBE ACCESS                  | PRODUCT    |       |       |            |          |
|*  7 |    CUBE ACCESS                  | TIME       |     1 |   100 |   103   (2)| 00:00:02 |
----------------------------------------------------------------------------------------------
 
Predicate Information (identified by operation id):
---------------------------------------------------
 
   7 - filter(SYS_OP_ATG(VALUE(KOKBF$),12,13,2)='CALENDAR_YEAR' AND
              SYS_OP_ATG(VALUE(KOKBF$),43,44,2)='TOTAL' AND
              SYS_OP_ATG(VALUE(KOKBF$),33,34,2)='TOTAL' AND
              SYS_OP_ATG(VALUE(KOKBF$),23,24,2)='TOTAL')
 
22 rows selected.

Example: Execution Plan for a Cube Join shows an execution plan for a query that joins a cube and a table. See "Joining Cubes to Tables and Views" for the query.

Example 3-9 Execution Plan for a Cube Join

PLAN_TABLE_OUTPUT
-------------------------------------------------------------------------------------------------
Plan hash value: 3634608218
-------------------------------------------------------------------------------------------------
| Id  | Operation                        |Name        |Rows | Bytes |TempSpc|Cost (%CPU)| Time    |
--------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                 |            |1464 |   128K|       | 1524  (94)| 00:00:19|
|   1 |  SORT ORDER BY                   |            |1464 |   128K|   152K| 1524  (94)| 00:00:19|
|*  2 |   CUBE JOIN                      |            |1464 |   128K|       | 1422 (100)| 00:00:18|
|   3 |    TABLE ACCESS FULL             |CUSTOMER_DIM|  61 |  2379 |       |    4   (0)| 00:00:01|
|   4 |    JOINED CUBE SCAN PARTIAL OUTER|            |     |       |       |           |         |
|   5 |     CUBE ACCESS                  |UNITS_CUBE  |     |       |       |           |         |
|   6 |     CUBE ACCESS                  |CHANNEL     |     |       |       |           |         |
|   7 |     CUBE ACCESS                  |PRODUCT     |     |       |       |           |         |
|*  8 |     CUBE ACCESS                  |TIME        |2520 |   125K|       | 1417 (100)| 00:00:18|
--------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access("CU"."SHIP_TO_ID"=SYS_OP_ATG(VALUE(KOKBF$),76,77,2))
   8 - filter(SYS_OP_ATG(VALUE(KOKBF$),32,33,2)='CY2006' AND
              SYS_OP_ATG(VALUE(KOKBF$),85,86,2)='TOTAL' AND 
              SYS_OP_ATG(VALUE(KOKBF$),65,66,2)='TOTAL')

22 rows selected.

Types of Execution Plans

Table: Descriptions of Execution Plans for Cubes and Dimensions describes the types of execution plans for cubes.

Table 3-1 Descriptions of Execution Plans for Cubes and Dimensions

Operation	Option	Description
`CUBE JOIN`	--	Joins a table or view on the left and a cube on the right.
`CUBE JOIN`	`ANTI`	Uses an antijoin for a table or view on the left and a cube on the right.
`CUBE JOIN`	`ANTI SNA`	Uses an antijoin (Single-sided Null Aware) for a table or view on the left and a cube on the right. The join column on the right (cube side) is `NOT NULL`. For example: SELECT cols FROM table WHERE table.c1 NOT IN (SELECT col FROM cube WHERE cube.col IS NOT NULL)
`CUBE JOIN`	`OUTER`	Uses an outer join for a table or view on the left and a cube on the right.
`CUBE JOIN`	`RIGHT SEMI`	Uses a right semijoin for a table or view on the left and a cube on the right.
`CUBE SCAN`	--	Uses inner joins for all cube access.
`CUBE SCAN`	`PARTIAL OUTER`	Uses an outer join for least one dimension, and inner joins for the other dimensions.
`CUBE SCAN`	`OUTER`	Uses outer joins for all cube access.