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

Jonathan Lewis,

		Thanks very much for your reply. Yes, in oracle 8i on sun solaris, the db block gets of fulltable scan is always 4block, no matter what the size of the table is. But in my tests in linux/817, it always show 12(8170 and 8172).I run the full scan again and again, but the value does not change.
		And another problem is why in oracle9i, there is no db_block_gets when doing full segment scan.I checked asktom.oracle.com, but unable to find the answer. And i also tested 9.0.1 on sun solaris , when very small, db_block_gets is 6,while larger tables(12K records from dba_tables), db_block_gets is 12.  
		Scanning the segment header caused the current mode read,is it because of scanning the buffer pool head and getting the cache buffer chains latch in exclusive mode,and the buffer head will be moved the other end lru list? why scanning the other data block does not cause the current read? Sorry, I asked to much, and maybe they are meanless, but if possible, I still want to know. 

		Sony kristanto, what kind of parameters do you think will affect the db_block_gets? I will post them.
        Thanks.

Regards
zhu chao
msn:chao_ping_at_163.com
www.happyit.net
www.cnoug.org(China Oracle User Group)

• 2003-01-22 00:33:00 ,you wrote£º=======

>Tablescans in Oracle 8 start with 4 current
>gets (db block gets) on the segment header
>block - in Oracle 9 tablescans start with
>2 consistent gets on the segment header.
>
>I can't tell you why you have 12 current gets
>rather than 4 - but if the tests aren't identical,
>the physical reads and extra current gets may
>be related to delayed cleanout on a first read.
>
>
>
>Regards
>
>Jonathan Lewis
>http://www.jlcomp.demon.co.uk
>
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>-----Original Message-----
>To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
>Date: 22 January 2003 07:42
>
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