RE: Optimizer path

From: Hameed, Amir <Amir.Hameed_at_xerox.com>
Date: Mon, 5 Mar 2012 16:06:05 -0500
Message-ID: <304F58144267C5439E733532ABC9A3A1144A1C14_at_USA0300MS02.na.xerox.net>

Hi Rodrigo,
The Index type is NORMAL.  

Thanks

From: Rodrigo Mufalani [mailto:rodrigo_at_mufalani.com.br] Sent: Monday, March 05, 2012 4:02 PM
To: Hameed, Amir
Cc: oracle-l_at_freelists.org
Subject: Re: Optimizer path  

Hi Amir,

  The index type used on IXRWI0_WIP_CMPL_IDX5 is NORMAL or FUNCTION-BASED? Best Regards,

Rodrigo Mufalani
Oracle Ace Member
http://www.mufalani.com.br
 <http://mufalani.com.br/site/wp-content/uploads/2012/01/logo.png>

Folks,
I have a statement, which produces the following plan, which is based on FTS: SELECT * FROM <TABLE_NAME>

WHERE reprocess_flag = 'Y'

AND processing_phase = 1

AND processing_status_code2 = 'Running'

AND processing_mode_code2 = 'Normal'

;

---

---

| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |

---

---

| 0 | SELECT STATEMENT | | 139K| 52M| 5158 (1)| 00:01:02 |

|* 1 | TABLE ACCESS FULL| TXRWI0_WIP_CMPL_INTF | 139K| 52M| 5158 (1)| 00:01:02 |

---

---

Predicate Information (identified by operation id):

---

1 - filter("PROCESSING_PHASE"=1 AND "REPROCESS_FLAG"='Y' AND

"PROCESSING_STATUS_CODE2"='Running' AND
"PROCESSING_MODE_CODE2"='Normal')

When the same statement is run with a little modification in the WHERE clause, it produces a different and more efficient execution plan:

SELECT * FROM <TABLE_NAME>

WHERE reprocess_flag = 'Y'

AND processing_phase = 1

AND upper(processing_status_code2) = 'RUNNING'

AND upper(processing_mode_code2 )= 'NORMAL'

;

---

---

| Id | Operation | Name | Rows |
Bytes | Cost (%CPU)| Time |

---

---

| 0 | SELECT STATEMENT | | 1 |
397 | 4 (0)| 00:00:01 |

|* 1 | TABLE ACCESS BY INDEX ROWID| TXRWI0_WIP_CMPL_INTF | 1 | 397 | 4 (0)| 00:00:01 |

|* 2 | INDEX RANGE SCAN | IXRWI0_WIP_CMPL_IDX5 | 1 | | 3 (0)| 00:00:01 |

---

---

Predicate Information (identified by operation id):

---

1 - filter("REPROCESS_FLAG"='Y')

2 - access("PROCESSING_PHASE"=1)

filter(UPPER("PROCESSING_STATUS_CODE2")='RUNNING' AND

UPPER("PROCESSING_MODE_CODE2")='NORMAL') Below is the what the index IXRWI0_WIP_CMPL_IDX5 looks like:

INDEX_NAME COLUMN_NAME COLUMN_POSITION

• ------------------------- ---------------

IXRWI0_WIP_CMPL_IDX5 PROCESSING_PHASE 1 PROCESSING_STATUS_CODE2 2 PROCESSING_MODE_CODE2 3 INDEX_NAME IND_ROWS DISTINCT_KEYS
CLUSTERING_FACTOR TAB_ROWS TAB_BLOCKS

• ---------- ------------- ----------------- ---------- ----------

IXRWI0_WIP_CMPL_IDX5 281189 1
11220 282400 18882

All of the columns of the index have bad selectivity, individually, as well as combined:

select processing_phase, processing_status_code2, processing_mode_code2 , count(*) from txrwi0_wip_cmpl_intf group by

processing_phase, processing_status_code2, processing_mode_code2

;

PROCESSING_PHASE PROCESSING_STATUS_CODE2 PROCESSING_MODE_CODE2 COUNT(*)

• ------------------------------
  ------------------------------ ----------
  

4 Completed Normal
283934

1 Completed Error
2

I have the following question:

• When the statement is run with functions in the WHERE clause, the optimizer decided to use the leading column of the index to fetch rows, even though the selectivity of that column was bad. What made the optimizer go that route and why it did not choose it with the first run?

The eventual solution of the problem is to use histograms on column PROCESSING_PHASE, which worked fine.

Thanks

Amir

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Received on Mon Mar 05 2012 - 15:06:05 CST