mincache=direct

[David S. Bell]

I have read in this forum that adding this option to the mounts for my Oracle database filesystems would be helpfull. in these same messages it says that I should exclude the log and index areas from this. Can someone explain why I would only do the data and not logs and index areas?

[Alan Riggs]

The recommendations I have seen from oracle are:
archive log, backups, database exports:
utilize unix buffer cache.

rollback, temp:
utilize mincache=dsync,convosync=dsync

datafiles, redo logs:
utilize mincache=direct,convosync=direct

I would also add nodatainlog for the datafiles (which includes data & index).

[James A. Donovan]

It surprises me that people would recommend not setting mincache=direct for index datafiles. As stated in the mount_vxfs man page, the mincache=direct value cause any writes without the O_SYNC flag and all reads to be handled as if the VX_DIRECT cacheing advisory was set.

As long as your Oracle block size is a multiple of your filesystem block size, I think you should use mincache=direct to avoid "double-buffering" your data.

Another good source for some info is the vxfsio man page.

[Bryan Hunter_1]

Alan - Do you have an Oracle document that gives the recommendations you mentioned. A recent request from Oracle for guidance was responded to with a "see HP" response.

[Bryan Hunter_1]

One possible reason for keeping the index areas in cache is as follows.

If you follow the recommendations, you may end up with 2 caches like this. The first one in Oracle has both data and index pages. The second in the OS would have mainly index pages presuming this box is nearly dedicated to Oracle. The OS cache can be much larger than the Oracle cache, thus creating a very large index cache. In this situation (especially if the application is index intensive), the benefit of having a very large index cache could exceed the cost of double caching.

Any comments please.

[Mark Mitchell]

These tools are becoming obsolete for giving you any real performance on todays systems. Since JFS or (Veritas) file systems are in use with HP. I would look at "Veritas Database edition for Oracle on HP-UX". It takes your vxfs file systems and submits them like they are raw, you get performance without giving up data protection. http://www.veritas.com/products/category/ProductDetail.jhtml?_requestid=18119