Re: SQL Query tuning help

From: <Jared.Still_at_radisys.com>
Date: Tue, 10 Sep 2002 12:32:57 -0700
Message-Id: <22528.293373@fatcity.com>

Dennis,

What is the distribution of sa.ret?

I didn't see it included in an index.

Jared

DENNIS WILLIAMS <DWILLIAMS_at_LIFETOUCH.COM> Sent by: root_at_fatcity.com
 09/10/2002 12:18 PM
 Please respond to ORACLE-L  

        To:     Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
        cc: 
        Subject:        SQL Query tuning help

I am trying to tune a SQL query on Oracle 8.1.6. I have tried several optimizations, but
so far have made no improvements. I would appreciate any suggestions.

SELECT am.lid, am.name
FROM am, so, sa
WHERE so.lid = am.lid

AND so.key_ = sa.so_key
AND am.active = 1
AND so.code = 11
AND sa.ret = 'SB'

ORDER BY am.name

Tables:

   am - 250,000 rows, 220,000 rows have active = 1, the others are 0.    so - 1.3 million rows, lid has 250,000 distinct values, key_ is unique,

             code has 12 values, evenly distributed.    sa - 1.3 million rows, ret has 281 values, fairly evenly distributed. so_key is pretty unique.

Now, you'll probably say there is essentially a 1-1 relationship between so
and sa. You are right, but the developer insists this flexibility is essential.

The query executes in 16 seconds and returns 185 rows. This is felt to be too slow for an online lookup screen.

                                 explain plan results:

                                 SELECT STATEMENT   Cost = 2955
                                   SORT ORDER BY
                                     HASH JOIN
                                       HASH JOIN
                                         TABLE ACCESS FULL SA
                                         TABLE ACCESS FULL SO
                                       TABLE ACCESS FULL AM

Here is what I've tried so far:

Using hints to force Oracle to use indexes.

Query Plan

---

---

SELECT STATEMENT Cost = 62031
  SORT AGGREGATE
    NESTED LOOPS

      HASH JOIN
        TABLE ACCESS BY INDEX ROWID SA
          INDEX FULL SCAN SO_KEY3
        TABLE ACCESS BY INDEX ROWID SO
          INDEX RANGE SCAN PRG_CODE3
      TABLE ACCESS BY INDEX ROWID AM
        INDEX UNIQUE SCAN LID6 

Timing result 25 minutes

Next I tried creating new indexes that combine both the accessing column as
well as the retrieved column, thinking that Oracle could get the result from
the index block and not need to retrieve the data block.

      create index test1 on am (lid, active);
      create index test2 on sa (so_key, code);

SELECT STATEMENT Cost = 2951
  SORT AGGREGATE
    HASH JOIN

      HASH JOIN
        INDEX FULL SCAN TEST2
        TABLE ACCESS FULL SO
      TABLE ACCESS BY INDEX ROWID AM
        INDEX RANGE SCAN TEST1
 

Hinting so Oracle will use the new indexes, for one table Oracle uses the index only and for the other table, Oracle hits both the index and table itself. Response time is slightly longer than the original query. At this point I'm fresh out of ideas, so any ideas would be appreciated. Thanks.  

Dennis Williams
DBA
Lifetouch, Inc.
dwilliams_at_lifetouch.com <mailto:dwilliams_at_lifetouch.com>

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Author: DENNIS WILLIAMS
  INET: DWILLIAMS_at_LIFETOUCH.COM

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