Index Fast Full Scans

Index Fast Full Scans are similar to Index Full Scans i.e they read index blocks in unsorted order, as they exist on disk.This scan does not use the index to probe the table, but reads the index instead of the table, essentially using the index itself as a table.

SQL_ID  fu0k5nvx7sftm, child number 0
-------------------------------------
select /*+ index_ffs(departments dept_id_pk) */ count(*) from departments

Plan hash value: 3940160378
--------------------------------------------------------------------------
| Id | Operation             | Name       | Rows  |Cost (%CPU)| Time     |
--------------------------------------------------------------------------
|  0 | SELECT STATEMENT      |            |       |    2 (100)|          |
|  1 |  SORT AGGREGATE       |            |     1 |           |          |
|  2 |   INDEX FAST FULL SCAN| DEPT_ID_PK |    27 |    2   (0)| 00:00:01 |
--------------------------------------------------------------------------

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s