RE: negative value for buffer cache hit ratio

From: Christopher Spence <cspence_at_FuelSpot.com>
Date: Tue, 07 Aug 2001 10:03:56 -0700
Message-ID: <F001.0036308D.20010807101351@fatcity.com>

Try this more accurate query:

select to_char(100 * misses / (hits + misses), '9990.00') || '%' miss_rate from ( select total_waits misses

              from sys.v_$system_event
            where event = 'db file sequential read' ),
         ( select sum(dbbget + conget - pread)  hits
             from sys.x_$kcbwds
           where inst_id = userenv('Instance') )

Also, send the actual values if this query still leads to similar results.

The difference here is it takes in account of direct writes.

"Do not criticize someone until you walked a mile in their shoes, that way when you criticize them, you are a mile a way and have their shoes."

Christopher R. Spence OCP MCSE MCP A+ RAPTOR CNA Oracle DBA
Phone: (978) 322-5744
Fax: (707) 885-2275

Fuelspot
73 Princeton Street
North, Chelmsford 01863

-----Original Message-----
Sent: Tuesday, August 07, 2001 1:51 PM
To: Multiple recipients of list ORACLE-L

Dear gurus !
I have a negative value for buffer cache hit ratio in my DB which is up for some 4 months . Any ideas why ? Thanks in advance.

SQL> SELECT (1 - (SUM(DECODE(a.name,'physical reads',value,0)) / 2 (SUM(DECODE(a.name,'consistent gets',value,0)) + 3 SUM(DECODE(a.name,'db block gets',value,0))))) * 100 "buffer cache hit ratio"
4 FROM v$sysstat a;

buffer cache hit ratio

-52.99284

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Author: Christopher Spence
INET: cspence_at_FuelSpot.com

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