How much can SEQUENCE drag down speed of SQL?
10%? 20%? Below my working case show you SEQUENCE drag down 600% speed of one SQL.
It is during my recently shooting of a job's performance issue, i notice this SQL in the job block.
This is quite a simple SQL, two tables join, only thing secial is that it is using a sequence GGGC_SSBA.SEQ_MIM_CCCC_PPPP_SSS.NEXTVAL:
dwxxxx2 > SELECT /*+ USE_HASH(S1 TM)*/ GGGC_SSBA.SEQ_MIM_CCCC_PPPP_SSS.NEXTVAL ,330404 ,TO_DATE('2012-12-18 06:45:18', 'YYYY-MM-DD HH24:MI:SS') ,TO_DATE('2012-12-18 06:45:18', 'YYYY-MM-DD HH24:MI:SS') ,TO_DATE('2100-12-31', 'YYYY-MM-DD') ,S1.MATNR AS MATNR ,S1.VKORG AS VKORG ,S1.VTWEG AS VTWEG ,S1.KONDM AS KONDM ,S1.DWERK AS DWERK ,S1.VMSTA AS VMSTA ,S1.VMSTD AS VMSTD ,S1.LVORM AS LVORM ,S1.DT_TM_XTR AS DT_TM_XTR ,S1.CDHDR_UDATE AS CDHDR_UDATE ,S1.PROVG AS PROVG FROM GEPC_TEMP_TABLE.KKK_MIM_XXXX_RRRR_SSS TM GEPC_SOURCE.EEEIE_ZZZZZ_MMML_SLS S1 WHERE TM.SOURCE_ROWID = S1.ROWID; 643418 rows selected. Elapsed: 00:01:00.21 Execution Plan ---------------------------------------------------------- Plan hash value: 3276368232 -------------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 36837 | 2590K| 759 (3)| 00:00:14| | 1 | SEQUENCE | SEQ_MIM_CCCC_PPPP_SSS | | | | | |* 2 | HASH JOIN | | 36837 | 2590K| 759 (3)| 00:00:14| | 3 | TABLE ACCESS FULL| KKK_MIM_XXXX_RRRR_SSS | 36837 | 359K| 29 (0)| 00:00:01| | 4 | TABLE ACCESS FULL| EEEIE_ZZZZZ_MMML_SLS | 643K| 38M| 724 (3)| 00:00:14| -------------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 2 - access("TM"."SOURCE_ROWID"="S1".ROWID) Statistics ---------------------------------------------------------- 128804 recursive calls 96793 db block gets 77309 consistent gets 661 physical reads 21141944 redo size 25998756 bytes sent via SQL*Net to client 472358 bytes received via SQL*Net from client 42896 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 643418 rows processed
From above red part we see the SQL esclape time is one minute.
That is too long after considerring the query's base tables data volumn, it should not take that much time.
We also notice that big "recursive calls" and "db block gets" Statistics.
It is very clear that they are caused by the sequence in the SQL.
So let's remove the sequence from the query and check again:
dwxxxx2 > SELECT /*+ USE_HASH(S1 TM)*/ 330404
,TO_DATE('2012-12-18 06:45:18', 'YYYY-MM-DD HH24:MI:SS')
,TO_DATE('2012-12-18 06:45:18', 'YYYY-MM-DD HH24:MI:SS')
,TO_DATE('2100-12-31', 'YYYY-MM-DD') ,S1.MATNR AS MATNR ,S1.VKORG AS
VKORG ,S1.VTWEG AS VTWEG ,S1.KONDM AS KONDM ,S1.DWERK AS DWERK
,S1.VMSTA AS VMSTA ,S1.VMSTD AS VMSTD ,S1.LVORM AS LVORM
,S1.DT_TM_XTR AS DT_TM_XTR ,S1.CDHDR_UDATE AS CDHDR_UDATE
,S1.PROVG AS PROVG FROM GEPC_TEMP_TABLE.KKK_MIM_XXXX_RRRR_SSS TM
GEPC_SOURCE.EEEIE_ZZZZZ_MMML_SLS S1 WHERE TM.SOURCE_ROWID = S1.ROWID;
643418 rows selected.
Elapsed: 00:00:10.23
Execution Plan
----------------------------------------------------------
Plan hash value: 2074598172
-------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 36837 | 2590K| 759 (3)| 00:00:14|
|* 1 | HASH JOIN | | 36837 | 2590K| 759 (3)| 00:00:14|
| 2 | TABLE ACCESS FULL| KKK_MIM_XXXX_RRRR_SSS | 36837 | 359K| 29 (0)| 00:00:01|
| 3 | TABLE ACCESS FULL| EEEIE_ZZZZZ_MMML_SLS | 643K| 38M| 724 (3)| 00:00:14|
-------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - access("TM"."SOURCE_ROWID"="S1".ROWID)
Statistics
----------------------------------------------------------
1 recursive calls
0 db block gets
44998 consistent gets
0 physical reads
0 redo size
21501260 bytes sent via SQL*Net to client
472358 bytes received via SQL*Net from client
42896 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
643418 rows processedWithout the sequence the job completes in 10 seconds.
In another word, the sequence drag down 600% speed of this SQL.
Let's check the sequence attribute:
dwxxxx2 >select * from dba_sequences where SEQUENCE_NAME='SEQ_MIM_CCCC_PPPP_SSS';
SEQUENCE_OWNER SEQUENCE_NAME INCREMENT_BY C O CACHE_SIZE LAST_NUMBER
-------------- --------------------- ------------ - - ---------- -----------
GGGC_SSBA SEQ_MIM_CCCC_PPPP_SSS 1 N N 20 109594869The CACHE_SIZE is 20.
20 is a default value, it is not suitable in our case.
I increase the value to 500 and re-execute the SQL.
This time:
dwxxxx2 > SELECT /*+ USE_HASH(S1 TM)*/ GGGC_SSBA.SEQ_MIM_CCCC_PPPP_SSS.NEXTVAL ,330404
,TO_DATE('2012-12-18 06:45:18', 'YYYY-MM-DD HH24:MI:SS')
,TO_DATE('2012-12-18 06:45:18', 'YYYY-MM-DD HH24:MI:SS')
,TO_DATE('2100-12-31', 'YYYY-MM-DD') ,S1.MATNR AS MATNR ,S1.VKORG AS
VKORG ,S1.VTWEG AS VTWEG ,S1.KONDM AS KONDM ,S1.DWERK AS DWERK
,S1.VMSTA AS VMSTA ,S1.VMSTD AS VMSTD ,S1.LVORM AS LVORM
,S1.DT_TM_XTR AS DT_TM_XTR ,S1.CDHDR_UDATE AS CDHDR_UDATE
,S1.PROVG AS PROVG FROM GEPC_TEMP_TABLE.KKK_MIM_XXXX_RRRR_SSS TM
GEPC_SOURCE.EEEIE_ZZZZZ_MMML_SLS S1 WHERE TM.SOURCE_ROWID = S1.ROWID;
643418 rows selected.
Elapsed: 00:00:29.60
Execution Plan
----------------------------------------------------------
Plan hash value: 3276368232
--------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 36837 | 2590K| 759 (3)| 00:00:14|
| 1 | SEQUENCE | SEQ_MIM_CCCC_PPPP_SSS | | | | |
|* 2 | HASH JOIN | | 36837 | 2590K| 759 (3)| 00:00:14|
| 3 | TABLE ACCESS FULL| KKK_MIM_XXXX_RRRR_SSS | 36837 | 359K| 29 (0)| 00:00:01|
| 4 | TABLE ACCESS FULL| EEEIE_ZZZZZ_MMML_SLS | 643K| 38M| 724 (3)| 00:00:14|
--------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("TM"."SOURCE_ROWID"="S1".ROWID)
Statistics
----------------------------------------------------------
5153 recursive calls
3870 db block gets
46287 consistent gets
0 physical reads
844460 redo size
25998756 bytes sent via SQL*Net to client
472358 bytes received via SQL*Net from client
42896 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
643418 rows processedSQL completes in 30 seconds. Also "db block gets" and "recursive calls" is much smaller then first serneriao--cache is 20.
30 seconds means still the sequence drag down 3 times of the sql's speed.
It is still not reasonable.
The DB have mutiple samiliar queries, I don't have enough free time to look deep into this. I may raise a ticket with oracle support to check this once i get free time.
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