11g new feature "Partition pruning based on bloom filtering" is what?

Question

While idly reading the Oracle 11g Database New Features I stumbled upon the following - BEGIN QUOTE:
1.11.1.2 Enhanced Partition Pruning Capabilities
Partition pruning now uses bloom filtering instead of subquery pruning. While subquery pruning was activated on a cost-based decision and consumed internal (recursive) resources, pruning based on bloom filtering is activated all the time without consuming additional resources.
END QUOTE
I haven't found any other references to bloom filtering in the manuals, and very few via google and MetaLink. So I am left wondering what the above paragraph actually means?
Best regards,
Hans Henrik Krohn

Answer 1

Hi Hans
The problem of subquery pruning is that part of the SQL statement is executed twice. Therefore, a cost-based decision is necessary to decide if it makes to do it or not...
To avoid this double execution they introduced join-filter pruning (which takes advantage of a bloom filter). Since this new method has a very small overhead, it makes always sense to use it if pruning can be used. With it you will see execution plans like the following one.
| Operation                           | Name    | Pstart| Pstop |
| HASH JOIN                           |         |       |       |
|  PART JOIN FILTER CREATE            | :BF0000 |       |       |
|   TABLE ACCESS BY GLOBAL INDEX ROWID| T       | ROWID | ROWID |
|    INDEX UNIQUE SCAN                | T_PK    |       |       |
|  PARTITION RANGE JOIN-FILTER        |         |:BF0000|:BF0000|
|   TABLE ACCESS FULL                 | T       |:BF0000|:BF0000|
-----------------------------------------------------------------HTH
Chris