Re: More blocks in buffer cache than object on disk

Well, there are read consistent copies of the table blocks. You may also have previous image copies if you have RAC. You can have RC copies, for many different SCN numbers.

On 2/26/20 4:45 PM, Rich J wrote:
> Hey all,
>
> In one of our 12.1.0.2 DBs, there's some discussion involving a table
> and/or its indexes.  In gathering info about the table, I see that
> while the table size is 683264 blocks (from DBA_SEGMENTS), there
> appears to be 1071098 blocks in the buffer cache for that table,
> according to V$BH.  That's ~8.4GB cache for a ~5.3GB table (8K block
> size).  Seems....excessive.
>
> Maybe my buffer cache query is at fault:
>
> SELECT
>      dbo.owner||'.'||dbo.object_name object_name,
>      bh.objd,
>      COUNT(*)*8192/1024/1024 size_mb,
>      count(*) size_blocks
> FROM
>      dba_objects DBO,
>      v$bh bh
> WHERE
>      dbo.data_object_id = bh.objd
>      and dbo.object_name = 'MYTABLE'
> GROUP BY
>      dbo.owner,
>      dbo.object_name,
>      bh.objd;
>
> If it matters, this instance is on AIX, has an SGA of ~130GB, non-ASM,
> non-AMM, and is a primary for ADG.  It's been up for about 40 days. 
> The ERP application that uses it gets bounced weekly due to middle
> tier Java entropy (so, no lingering transactions).
>
> Thoughts?
>
> Thanks,
> Rich

-- 
Mladen Gogala
Database Consultant
Tel: (347) 321-1217


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