what GetMemoryChunkSpace() works on IIUC.
Am i correct here?
That's interesting an interesting realization. You're right that we
cannot use GetMemoryChunkSpace() in that case.
However, I'm wondering if the better approach wouldn't be to change fd.c
to use a long-lived memory context. Then all bookkeeping would happen
automatically and the memory size could simply be reported via existing
memory context stats infrastructure.
Not entirely sure though if there's some roadblock when switching to a
memory context.
I don't see any issue with this either. However, the only benefit we would
gain is using existing infrastructure but only for backend vfd cache memory
(i.e cache_bytes).
Everything else stays the same (counters, cluster-wide memory); therefore,
if there's no other benefit to replacing with memory contexts, maybe it's
not worth it.
The biggest benefit in my view is consistency with the rest of PostgreSQL.
That is from a usage point of view as well as from a coding point of view.
If you want, I can give that a try and share a patch with you if successful.
--
David Geier
