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Rule of thumb for CACHE_SIZE

Former Member
0 Kudos

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

Accepted Solutions (1)

Accepted Solutions (1)

markus_doehr2
Active Contributor
0 Kudos

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

Former Member
0 Kudos

Hi Markus,

so I was right.

The server was created as a vmware clone, and it was forgotten to add additional RAM. In next maintainance window this will be done.

Thank you.

Best regards

Christian

markus_doehr2
Active Contributor
0 Kudos

> The server was created as a vmware clone, and it was forgotten to add additional RAM. In next maintainance window this will be done.

Be aware that "cloning" a SAP instance using VMWare tools and renaming the host is unsupported.

Markus

Former Member
0 Kudos

Hi Markus,

the container was empty (without SAP) when it was cloned. So this should be supported.

Best regards

Christian

Answers (0)