Re: Buffer cache hit very low...!!!
- From: Lou Fangxin <anysql@xxxxxxxxx>
- To: chiragdba@xxxxxxxxx
- Date: Wed, 14 Sep 2005 08:51:53 +0800
You need to check the time interval value, not the absolute value in
v$sysstat, this value can be reseted due to overflow.
On 9/14/05, Chirag DBA <chiragdba@xxxxxxxxx> wrote:
>
> Hi Team,
> My OEM shows buffer cache hit ratio as 28% and library cache as 99%.
> Another query shows different results for buffer cache.
>
> SQL> SELECT NAME,100-PHYSICAL_READS/(DB_BLOCK_GETS + CONSISTENT_GETS) FROM
> V$BUFFER_POOL_STATISTICS;
>
> NAME 100-PHYSICAL_READS/(DB_BLOCK_GETS+CONSISTENT_GETS)
> -------------------- --------------------------------------------------
> DEFAULT 99.9072457
>
> SQL> show sga
>
> Total System Global Area 252273320 bytes
> Fixed Size 434856 bytes
> Variable Size 150994944 bytes
> Database Buffers 100663296 bytes
> Redo Buffers 180224 bytes
>
> And my db_block_buffers show value as 0.
>
> but it should be the value of database buffers / db_block_size .
>
> SQL> show parameter db_block
>
> NAME TYPE VALUE
> ------------------------------------ ----------- ----------------------
> db_block_buffers integer 0
> db_block_checking boolean FALSE
> db_block_checksum boolean TRUE
> db_block_size integer 8192
>
> Is really my buffer cache hits very low?
>
> Regards - Chirag
>
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