Cache behavior changes on restarting DB.

Question

I selected 10 records from db - that time the cache size was 3 blocks.
I took reading for 100, 1000, etc,. records in the same way and cache size was noticed.
I noticed a strainge behavior that after restarting the machine, the previous reading was different.
That is, for 10 records the cache size was 20 blocks.. same behaviour repeats on each restarting.
May i know if anyone noticed the behavior?

Answer 1

Manu wrote:
Hi Amen,
The database version is 11g R2 64bit.
Number of blocks used is calclulated by
SELECT SUM(number_of_blocks)
FROM
(SELECT o.object_name, h.status, count(*) number_of_blocks
FROM V$BH h, DBA_OBJECTS o
WHERE h.objd=o.data_object_id AND o.owner NOT IN('SYS','SYSTEM','SYSMAN')
AND h.status NOT IN('free') GROUP BY o.object_name,h.status
ORDER BY count(*) DESC)
Could be effects of delayed block cleanout.
Could be effects of dynamic sampling
For an empty cache (after startup or flush buffer cache in 11g) could be related to cache warmup - as indicated by statistic "physical reads prefetch warmup"
But the question you have to ask yourself is: "Do you have any problem that you're trying to address - or is this just curiosity?"
Regards
Jonathan Lewis