Rule of thumb for CACHE_SIZE

Hi all,
I do have a system outsourced, where the DB (MAXDB 7.6.05) runs on a single SLES 10 server.
This server has got 16 GB RAM. The CACHE_SIZE is configured to 20 GB (2500000 pages) and a top shows me, that from the 40 GB swap 20 GB are used (file system cache is so low, that it can be ignored) ... and swapd runs with at least 6% CPU all the time.
Is this a good situation? Not for me! Does anybody have a rule of thumb for CACHE_SIZE?
I would say 75 % of RAM should be the highest value... any othe suggestion?
Thank you!
Christian

Cache must always fit in the physical RAM. The purpose of the cache is to hold data in the memory that it doesn't need to be read again and again from the disk. If you now configure that cache bigger than the physical available RAM (minus application minus operating system) the system will start swapping/paging in and out and hence slowing down the full system.
Ideally the machine is not swapping at all and all data is in the memory.
Markus

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