Hi, dba friends:
Look at the following test result, the first one is from oracle9.2, and the
second is from the oracle 817. The table is same, and as you see, the execution path
is the same.
But there is difference in statistics: db_block_gets, in oracle92, it is 0,
and in oracle817, it is not.
And i noticed that in oracle8i, all sql that does only query with execution
path full scan of table/index,there will always be db_block_gets, while in 9i, select
won't make db_block_gets.
As tom said, db_block_gets is increased when data is accessed for update, how
does this query generate this statistics?
ORA92> select count(*) from abc;
COUNT(*)
----------
10000
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=6 Card=1)
1 0 SORT (AGGREGATE)
2 1 TABLE ACCESS (FULL) OF 'ABC' (Cost=6 Card=10000)
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
27 consistent gets
0 physical reads
0 redo size
379 bytes sent via SQL*Net to client
503 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
ORA817> select count(*) from abc;
COUNT(*)
----------
10000
Elapsed: 00:00:00.26
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE
1 0 SORT (AGGREGATE)
2 1 TABLE ACCESS (FULL) OF 'ABC'
Statistics
----------------------------------------------------------
0 recursive calls
12 db block gets
28 consistent gets
24 physical reads
0 redo size
367 bytes sent via SQL*Net to client
425 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
Regards
zhu chao
msn:[EMAIL PROTECTED]
www.happyit.net
www.cnoug.org(China Oracle User Group)
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