Tom Arthurs wrote:
Yes, shared buffers in postgres are not used for caching

Shared buffers in Postgres _are_ used for caching, they just form a secondary cache on top of the kernel's IO cache. Postgres does IO through the filesystem, which is then cached by the kernel. Increasing shared_buffers means that less memory is available for the kernel to cache IO -- increasing shared_buffers has been shown to be a net performance loss beyond a certain point. Still, there is value in shared_buffers as it means we can avoid a read() system call for hot pages. We can also do better buffer replacement in the PG shared buffer than the kernel can do (e.g. treating IO caused by VACUUM specially).

My biggest challenge with solaris/sparc is trying to reduce context

It would be interesting to see if this is improved with current sources, as Tom's bufmgr rewrite should have hopefully have reduced this problem.


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