Tuning DB_BLOCK_BUFFER

HI everyone,

Is it going to hurt the database performance if I increase the number of DB_BLOCK_BUFFER to a large number? I am absolutely sure that the RAM and SHMMAX parameter is set in a way that it is big enough for the whole SGA to settle in. And the Oracle Version is 7.3.4.0.1 on Solaris 2.5.1. The cache hit ratio used to be 78%. I tried to increase it to 80s by increasing the number of DB_BLOCK_BUFFER. So the whole area of SGA goes from 185MB to 190MB (not too big for a normal database). ANd then the cache hit ratio dropped to around 40%!!!!

I know that you can set the db_lru_extended_statistic (or something similar) to check the the performance increase for each addition of db_block_buffer. But since that database is in production for 24*7. There is no way I can shutdown the database and check for it. Does anyone have any idea why this is the case?

I also checked the paging and swapping and the CPU utilization on the box, everything look normal.
ANd since we have application running on that database, the transactions are more or less the same daily.

Thanks very much

Winnie Received on Tue Sep 15 1998 - 21:40:37 CDT