Re: Add pg_stat_vfdcache view for VFD cache statistics

>>> Yes of course, I’d be happy to take a look.
>> Attached is the patch. It's pretty small and passes regress tests.
>>
> Nice one.
> Few comments on it:
> #1:
> + oldcontext = MemoryContextSwitchTo(VfdCxt);
> + newVfdCache = repalloc_array(VfdCache, Vfd, newCacheSize);
> + MemoryContextSwitchTo(oldcontext);
>
> Can't we just do this?
> + newVfdCache = repalloc_array(VfdCache, Vfd, newCacheSize);
>
> because repalloc doesn't need CurrentMemoryContext.

Yes. You can then make it even simpler and get rid of newVfdCache via

VfdCache = repalloc_array(VfdCache, Vfd, newCacheSize);

> #2:
> + newDescs = MemoryContextAllocExtended(VfdCxt,
> + newMax * sizeof(AllocateDesc), MCXT_ALLOC_NO_OOM);
> if (newDescs == NULL)
> return false;
> + memcpy(newDescs, allocatedDescs, maxAllocatedDescs *
> sizeof(AllocateDesc));
> + pfree(allocatedDescs);
>
> We can also just replace it with:
> + newDescs = repalloc_array_extended(allocatedDescs, AllocateDesc,
> + newMax, MCXT_ALLOC_NO_OOM);
> Correct?

Yes.

v7-0001: looks good to me.

v7-0003: I'm wondering if we still want cache_bytes in pg_stat_vfdcache,
now where it's exposed via pg_backend_memory_contexts. It seems to me
that other stats functionality also doesn't expose memory info that is
accessible via pg_backend_memory_contexts. But I'm not completely sure
what's best here.

--
David Geier