Re: a explain plan question
- From: Wolfgang Breitling <breitliw@xxxxxxxxxxxxx>
- To: ax.mount@xxxxxxxxx
- Date: Tue, 30 Jan 2007 09:25:55 -0700
At 09:08 AM 1/30/2007, amonte wrote:
This is puzzling me
a change from NL to HASH (by using USE_HASH) then plan changed which
is obvious but also the stats? TUH_NVPAGINA which has over 2000
million of rows now shows correct estimation under HASH but showed a
miserable 6 million using NL. What is causing this?
In the NL plan there is a flter predicate on TUH_NVPAGINA. It will
read TUH_NVPAGINA an estimated 30 times (rows from step 3) returning
~6M rows each time for an estimated 30*6M = 180M rows coming out of
the nested loop (step 2 rows = 182M)
In the HA plan it reads TUH_NVPAGINA once, all 2163M rows (there is
no a access or filter predicate for step 5). Those 2163M rows are
than hashed in step 2 against the 30 rows out of step3 returning the
same estimated 182M rows.
--------------------------------------------------------------------------------------------
| 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 |
--------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - filter("TUD_FEDIA"."ID_MES"=TO_NUMBER(:Z))
5 - filter("TUH_NVPAGINA"."FE_DIA"="TUD_FEDIA"."FE_DIA")
--------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes |
Cost | Pstart| Pstop |
--------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 934 | 49502
| 1555K| | |
| 1 | SORT GROUP BY | | 934 | 49502
| 1555K| | |
|* 2 | HASH
JOIN | | 182M| 9213M| 1347K| | |
|* 3 | TABLE ACCESS FULL | TUD_FEDIA | 30 | 480
| 3 | | |
| 4 | PARTITION RANGE
ITERATOR| | | | | KEY | KEY |
| 5 | TABLE ACCESS FULL |
TUH_NVPAGINA | 2163M| 74G| 1330K| KEY | KEY |
--------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("TUH_NVPAGINA"."FE_DIA"="TUD_FEDIA"."FE_DIA")
3 - filter("TUD_FEDIA"."ID_MES"=TO_NUMBER(:Z))
Regards
Wolfgang Breitling
Centrex Consulting Corporation
www.centrexcc.com
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