Execution time of query on different indexes

Hello,
I have a query on the table, the execution time has hugh difference using different indexes on the table. The table has about 200,000 rows. Any explaination on it?
Thanks,
create table TB_test
( A1 number(9),
A2 number(9)
select count(*) from TB_test
where A1=123 and A2=456;
A. With index IDX_test on column A1:
Create index IDX_test on TB_test(A1);
Explain plan:
SELECT STATEMENT
Cost: 3,100
SORT AGGREGATE
Bytes: 38 Cardinality: 1
TABLE ACCESS BY INDEX ROWID TABLE TB_test
Cost: 3,100 Bytes: 36 Cardinality: 1
INDEX RANGE SCAN INDEX IDX_test
Cost: 40 Cardinality: 21,271
Execution time is : 5 Minutes
B. With index IDX_test on column A1 and A2:
Create index IDX_test on TB_test(A1, A2);
Explain plan:
SELECT STATMENT
Cost: 3 Bytes: 37 Cardinality: 1
SORT AGGREGATE
Bytes: 37 Cardinality: 1
INDEX RANGE SCAN INDEZ IDX_test
Cost: 3 Bytes 37 Cardinality:1
Execution time is: 1.5 Seconds

Additional you should check how many values you have in your table for the specific column values.
The following select might be helful for that.
select count(*) "total_count"
,count(case when A1=123 then 1 end) "A1_count"
,count(case when A1=123 and A2=456 then 1 end) "A1andA2_count"
from TB_test;Share your output of this.
I expect the value for A1_count still to be high. But the value for A1+A2_count relatively low.
However 5 minutes is far to long for such a small table. Even if you run it on a laptop.
There must be a reason why it is that slow.
First thing to consider would be to update your statistics for the table and the index.
Second thing could be that the table is very sparsly fillled. Meaning, if you frequently delete records from this table and load new data using APPEND hint, then the table will grow, because the free space from the deletes is never reused. Any table access in the execution plan, will be slower then needed.
A similar thing can happen, if many updates on previously empty columns are made on a table (row chaining problem).
So if you explain a little, how this table is filled and used, we could recognize a typical pattern that leads to performance issues.
Edited by: Sven W. on Nov 28, 2012 5:54 PM

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907814 wrote:
I am a C/C++ programmer and newbie to database. I find weird case to my company database. oracle 10g.
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4
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4.26
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12
2.77
17.88
11,179
1
732
2.13
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4.81
14.36
348
0
1
0.00
INDUS_TMP_DATA01
44,020
3
4.41
16.55
244
0
1,587
4.79
SYSAUX
19,373
1
19.81
1.05
14,489
1
0
0.00
INDUS_LOG_INDX01
17,559
1
4.75
1.96
2,837
0
2
0.00
SYSTEM
7,881
0
12.15
1.04
1,361
0
109
7.71
INDUS_TMP_INDX01
1,873
0
11.48
13.62
231
0
0
0.00
INDUS_MST_INDX01
256
0
13.09
1.04
194
0
2
10.00
UNDOTBS1
70
0
1.86
1.00
60
0
0
0.00
STG_DATA01
63
0
1.27
1.00
60
0
0
0.00
USERS
63
0
0.32
1.00
60
0
0
0.00
INDUS_LOB_DATA01
62
0
0.32
1.00
60
0
0
0.00
TS_AUDIT
62
0
0.48
1.00
60
0
0
0.00
18th Oct
Tablespace
Reads
Av Reads/s
Av Rd(ms)
Av Blks/Rd
Writes
Av Writes/s
Buffer Waits
Av Buf Wt(ms)
INDUS_TRN_DATA01
980,283
91
1.40
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The AWR reports for two days with same sqlID with different execution plan and Elapsed Time (s), Executions time please help me to find out what is reason for this change.
Please find the below detail 17th day my process are very slow as compare to 18th
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Regards
Mahir M. Quluzade

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