Cache hash chains

From: Paul Harrison <cure_at_austin.rr.com>
Date: Tue, 3 Mar 2015 15:50:05 -0600
Message-ID: <003c01d055fc$032e4d30$098ae790$_at_austin.rr.com>

Hi Team,  

The query below returns 4 rows. The database object BUFFCACHETEST has 4 database buffer headers(doubled linked list) attached to a hash bucket? Why do we have 4 database buffer headers linked to 1 working data set( database buffer cache block )?  

select HLADDR, decode(STATE,0,'free',1,'xcur',2,'scur',3,'cr', 4,'read',5,'mrec',6,'irec',7,'write',8,'pi', 9,

'memory',10,'mwrite',11,'donated', 12,'protected', 13,'securefile', 14,'siop',15,'recckpt', 16,

'flashfree', 17, 'flashcur', 18, 'flashna') as STATE, PRV_HASH, NXT_HASH,

                       BA, DBARFIL, DBABLK   

            from X$BH where OBJ = 78451 and DBABLK = 196393;

 

##

update BUFFCACHETEST set NUM=13 where NUM=3;  

HLADDR STATE PRV_HASH NXT_HASH BA

• ---------- ---------------- ---------------- ---------------- DBARFIL DBABLK---------- ----------

000000007A3E3548 xcur 000000007A3E38E8 0000000066FD2FF0 0000000066F04000 1 196393  

000000007A3E3548 cr 0000000066FD2EA8 0000000066FD3138 0000000066F06000 1 196393  

000000007A3E3548 cr 0000000066FD2FF0 0000000068FB7C50 0000000066F08000 1 196393    

HLADDR STATE PRV_HASH NXT_HASH BA

• ---------- ---------------- ---------------- ---------------- DBARFIL DBABLK---------- ----------

000000007A3E3548 cr 0000000066FD3138 000000007A3E38E8 0000000068C5E000 1 196393    

Thanks,

Paul

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Received on Tue Mar 03 2015 - 22:50:05 CET