Re: a explain plan question
- From: Wolfgang Breitling <breitliw@xxxxxxxxxxxxx>
- To: ax.mount@xxxxxxxxx
- Date: Tue, 30 Jan 2007 08:22:28 -0700
At 07:43 AM 1/30/2007, amonte wrote:
Hi
I have this query
SNIP
and this plan
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=1022392 Card=934
Bytes=49502)
1 0 SORT (GROUP BY) (Cost=1022392 Card=934 Bytes=49502)
2 1 NESTED LOOPS (Cost=814767 Card=182275095 Bytes=9660580035)
3 2 TABLE ACCESS (FULL) OF 'TUD_FEDIA' (Cost=3 Card=30 Bytes=480)
4 2 PARTITION RANGE (ITERATOR)
5 4 TABLE ACCESS (FULL) OF 'TUH_NVPAGINA' (Cost=27159
Card=5992606 Bytes=221726422)
--------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes |
Cost | Pstart| Pstop |
--------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 934 | 49502
| 1022K| | |
| 1 | SORT GROUP BY | | 934 | 49502
| 1022K| | |
| 2 | NESTED
LOOPS | | 182M| 9213M| 814K| | |
|* 3 | TABLE ACCESS FULL | TUD_FEDIA | 30 | 480
| 3 | | |
| 4 | PARTITION RANGE
ITERATOR| | | | | KEY | KEY |
|* 5 | TABLE ACCESS FULL | TUH_NVPAGINA | 5992K| 211M|
27159 | KEY | KEY |
--------------------------------------------------------------------------------------------
SNIP
I was wondering how to read this plan, the order of steps. From old
set autotrace trace exp it seems to me that step 5 is the first step?
Unless I'm completely mistaken, the first step is to access the
driving table of the nested loop join, i.e. step 3. Besides, if it
didn't it wouldn't have the information for the filter predicate for step 5
An interesting side-observation (for me at least) was that the M
stands for MB as in 1,048,576=1024*1024, not Million as in 1,000,000.
I wouldn't intuitively count rows in multiples of 1024.
Regards
Wolfgang Breitling
Centrex Consulting Corporation
www.centrexcc.com
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