To the best of my knowledge, smgr is a layer that abstract the storage operations. Therefore, it is a good place to control or collect information the storage operations without touching the physical storage layer.
Moreover, smgr is coming with actual disk IO operation (not consider the OS cache) for postgres. So we do not need to worry about the buffer management in postgres.
It will make the purpose of hook is pure: a hook for actual disk IO.
Regards,
Haozhou
On Wed, Dec 26, 2018 at 1:56 PM Michael Paquier <michael@paquier.xyz> wrote:
On Wed, Nov 21, 2018 at 09:47:44AM -0500, Robert Haas wrote: > +1 for adding some hooks to support this kind of thing, but I think > the names you've chosen are not very good. The hook name should > describe the place from which it is called, not the purpose for which > one imagines that it will be used, because somebody else might imagine > another use. Both BufferExtendCheckPerms_hook_type and > SmgrStat_hook_type are imagining that they know what the hook does - > CheckPerms in the first case and Stat in the second case.
I personally don't mind making Postgres more pluggable, but I don't think that we actually need the extra ones proposed here at the layer of smgr, as smgr is already a layer designed to call an underlying set of APIs able to extend, unlink, etc. depending on the storage type.
> For this particular purpose, I don't immediately see why you need a > hook in both places. If ReadBuffer is called with P_NEW, aren't we > guaranteed to end up in smgrextend()?
