Re: same sql: different db block gets in different oracle version

Cho,

This is not unusual. I suspect your db_cache_size (or db_block_buffers) in 9.2 is more than db_block_buffers in 8.1. When you do a FTS, all the blocks are loaded into the buffers first time so 'db block gets' is a non zero value (it's the physical IO). The next time you do this, the blocks are found in the buffer already, so there is no physical IO, hence a zero value for 'db block gets'. However, your logical reads (consistent gets) should be the same and they are the same. In 817, run the query once again and see the 'db block gets' , it should be 0. If not then check if db_block_buffers is less than db_cache_size (or db_block_buffers) in 9.2.

HTH. Arup

• Original Message ----- To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com> Sent: Wednesday, January 22, 2003 1:53 AM

> 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:chao_ping_at_163.com
> www.happyit.net
> www.cnoug.org(China Oracle User Group)
>
>
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> Author: chao_ping
> INET: chao_ping_at_vip.163.com
>
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-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.net
-- 
Author: Arup Nanda
  INET: arupnanda_at_hotmail.com

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