RE: Delete Performance Issue

From: Ken Naim <kennaim_at_gmail.com>
Date: Thu, 21 Dec 2006 14:29:21 -0500
Message-ID: <003601c72536$528be4f0$68b016ac@KenHome>

Deleting 2.3 million rows takes time especially in 65 million rows table. The way I might handle this is load a global temporary table with the values returned by the subquery and "create table as select " a new table with the data you want add the index and them swap the names. If that is not an option try loading the values into a temp table and then doing the delete with a not in and add an index to the runseq field.

Ken

From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Don Doo
Sent: Thursday, December 21, 2006 12:47 PM To: oracle-l_at_freelists.org
Subject: Delete Performance Issue

Hi,
We are facing a serious performance
issue. This is a delete statement and
it takes 4 hours to delete 2.3 million
rows from a 65 million row table.
The c_trace table has only one index
(the primary key) The table is not
partitioned (we don't have the budget
to pay for partition option) Other tables have less than 5000 rows.
The sub-query returns 3 to 6 rows
depending on the values
Query
delete from c_trace
where targetperiod= 200612
and RUNSEQ in (select

 RunSeq from   C_Run pr,
               C_Summary ss,
               C_Stage st
      where  pr.RunSeq = ss.RunSeq
                and    ss.stageType = st.stageType
                and    st.name = 'load' 
              and    pr.period = 361
       and    ss.Active   = 'yes')

The V$session_longops shows
1 select OPNAME||' '||MESSAGE||' '||ELAPSED_SECONDS from v$session_longops
2* where sql_hash_value=2467621466
SQL> /
OPNAME||''||MESSAGE||''||ELA

Hash Join Hash Join:  : 6592 out of 6592 Blocks done  13688
Hash Join Hash Join:  : 6272 out of 6272 Blocks done  12753
Hash Join Hash Join:  : 6272 out of 6272 Blocks done  13594
Hash Join Hash Join:  : 7488 out of 7488 Blocks done  14050

Looks like it takes 14050 seconds to complete the hash join which matches the time taken to complete the delete. select HASH_VALUE,CPU_TIME,elapsed_time/(1000000*60),

      fetches,disk_reads,
             BUFFER_GETS,ROWS_PROCESsed
                  from v$sql where hash_value = 2467621466
HASH_VALUE   CPU_TIME     FETCHES DISK_READS BUFFER_GETS ROWS_PROCESSED
---------- ---------- ------------------------- ---------- ----------
----------- --------------
2467621466  193010000                0                      1265770
13820713         2325397

Oracle version 9.2.0.4
Hash_area_size 8 MB
Sort_area_size 4 MB
Statistics are current..
We are using ASSM for these tables.
I would really appreciate any ideas to improve this statement. We cannot do a event trace
here until mid of January next year because we are behind the SLA and don't want to make it slower.
Regards,
Don

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Received on Thu Dec 21 2006 - 13:29:21 CST