Re: Long-running SQL

Cherie_Machler_at_gelco.com wrote:
>
> We have a statement that I feel takes too long to run in a nightly data
> load.
> The table it runs against has 386,000 records. It runs for about 10
> seconds
> on average. We're only loading about 50,000 records a night but this
> statement
> is running during the majority of the 9-hour load time. This is causing
> the
> load to run longer than our allowable window and causing me untold
> headaches.
> If anyone has any suggestions to make this run faster, I'd be greatly
> appreciative.
>
> The columns in the where statement are all part of an index. However,
> the functions on the columns add additional execution time and complexity.
>
> This is an 8.0.4 database so I can not make this a function-based index.
>
> I put this in a couple of SQL tuning tools and came up with no valid
> alternatives.
> I can't help thinking that the statement could be rewritten into a couple
> of statements
> so that it would be more efficient. However, I'm not skilled enough with
> SQL to
> do it. Perhaps someone else is. Here's the code.
>
> SELECT /*+ INDEX(EXP_COST_CENTER_DIM EXP_COST_CENTER_DIM_IDX1) + */
> EXP_COST_CENTER_KEY
> FROM EXP_COST_CENTER_DIM
>
> WHERE ACCOUNT_NUMBER = :b1 AND
> NVL(ORG_LEVEL_1_VALUE,'NONE') = NVL(:b2,'NONE') AND
> NVL(ORG_LEVEL_2_VALUE,'NONE') = NVL(:b3,'NONE') AND
> NVL(ORG_LEVEL_3_VALUE,'NONE') = NVL(:b4,'NONE') AND
> NVL(ORG_LEVEL_4_VALUE,'NONE') = NVL(:b5,'NONE') AND
> NVL(ORG_LEVEL_5_VALUE,'NONE') = NVL(:b6,'NONE') AND
> NVL(ORG_LEVEL_6_VALUE,'NONE') = NVL(:b7,'NONE') AND
> NVL(ORG_LEVEL_7_VALUE,'NONE') = NVL(:b8,'NONE') AND
> NVL(ORG_LEVEL_8_VALUE, 'NONE')= NVL(:b9,'NONE') AND
> ROWNUM = 1
>
> SQL> desc exp_cost_center_dim
> Name Null? Type
> ------------------------------- -------- ----
> EXP_COST_CENTER_KEY NOT NULL NUMBER(7)
> ACCOUNT_NUMBER NOT NULL NUMBER(9)
> BATCH_WINDOW_DATE_KEY NOT NULL NUMBER(5)
> ORG_LEVEL_1_VALUE VARCHAR2(20)
> ORG_LEVEL_2_VALUE VARCHAR2(20)
> ORG_LEVEL_3_VALUE VARCHAR2(20)
> ORG_LEVEL_4_VALUE VARCHAR2(20)
> ORG_LEVEL_5_VALUE VARCHAR2(20)
> ORG_LEVEL_6_VALUE VARCHAR2(20)
> ORG_LEVEL_7_VALUE VARCHAR2(20)
> ORG_LEVEL_8_VALUE VARCHAR2(20)
> DATA_SOURCE_MOD_DATETIME NOT NULL DATE
> DATA_WAREHOUSE_MOD_DATETIME NOT NULL DATE
> DATA_MART_MOD_DATETIME NOT NULL DATE
>
> SQL> select column_name from dba_ind_columns where index_name
> ='EXP_COST_CENTER_D
> IM_IDX1';
>
> COLUMN_NAME
> --------------------------------------------------------------------------------
> ACCOUNT_NUMBER
> ORG_LEVEL_1_VALUE
> ORG_LEVEL_2_VALUE
> ORG_LEVEL_3_VALUE
> ORG_LEVEL_4_VALUE
> ORG_LEVEL_5_VALUE
> ORG_LEVEL_6_VALUE
> ORG_LEVEL_7_VALUE
> ORG_LEVEL_8_VALUE
>
> SQL> select column_name from dba_ind_columns where index_name
> ='EXP_COST_CENTER_D
> IM_PK';
>
> COLUMN_NAME
> --------------------------------------------------------------------------------
> EXP_COST_CENTER_KEY
>
> Thanks,
>
> Cherie Machler
> Oracle DBA
> Gelco Information Network
>

Cherie,

   I have only seen pieces of what I was expecting, so I am stepping in somewhat belatedly :
 o as several people underlined, your NVL functions are performance killers. Basically, the only usable column in your concatenated index happens to be ACCOUNT_NUMBER. Whether Oracle decides or not to use it is not very relevant, the point is that it's a rather useless index for this query.
 o I see two ways out :

• Either you make all your ORG_LEVEL_n_VALUE columns NOT NULL, and modify the table so as to define NONE (or anything else) as default value. It may, though, not be totally acceptable and will certainly cause a good deal of internal fragmentation when you'll do it. That said, your table is not enormous and can be reorganized afterwards. You will then be able to remove all left-hand side NVLs and the index will be usable and, in all likelihood, used.
• Or you create a function-based index on (ACCOUNT_NUMBER, NVL(ORG_LEVEL_1_VALUE,'NONE'), NVL(ORG_LEVEL_2_VALUE,'NONE'), NVL(ORG_LEVEL_3_VALUE,'NONE'), NVL(ORG_LEVEL_4_VALUE,'NONE'), NVL(ORG_LEVEL_5_VALUE,'NONE'), NVL(ORG_LEVEL_6_VALUE,'NONE') = NVL(:b7,'NONE'), NVL(ORG_LEVEL_7_VALUE,'NONE'), NVL(ORG_LEVEL_8_VALUE, 'NONE')) which will take more space than the curent index but will be directly usable by the query.

-- 
HTH,

Stephane Faroult
Oriole Software
-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: Stephane Faroult
  INET: sfaroult_at_oriole.com

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