disk cache useful?

We currently have an IBM RS/6000 C20 (Power PC 604, 64 Mb RAM, 2.2Gb disk) which is running AIX V4.1.4 and Oracle 7.1.6.

We are debating whether an L2 cache would be worth purchasing for this machine. At the moment, the database is pre-production but eventually we plan to have as many as 150 concurrent users each doing about 1 database transaction (lookup and/or update) per minute.

I maintain that the L2 cache would have almost no impact on performance in this scenario. My reasoning is that:
1. Any data that's in the L2 cache would also be in the oracle cache.

(Because Oracle maintains its own cache for data blocks and this cache
   is larger than the L2 cache,)

2. Any data that wouldn't be in the Oracle cache would also not be in the L2 cache.

(Because A. the Oracle cache is larger, and B. the L2 cache is used for all disk
     I/O not just disk I/O related to the database.)

My guess is that if we want to improve response time, more RAM and/or a RAID disk system would be a better place to invest than in an L2 cache.

Have I missed something here?

Thanks.

Scott Winger
LAN administrator
UW-Madison Division of Business Services swinger_at_mailsrvr.bussvc.wisc.edu Received on Mon Jan 22 1996 - 00:00:00 CET