Re: Make MemoryContextMemAllocated() more precise

On Mon, Mar 16, 2020 at 2:45 PM Jeff Davis <pgsql(at)j-davis(dot)com> wrote:
> Attached is a patch that makes mem_allocated a method (rather than a
> field) of MemoryContext, and allows each memory context type to track
> the memory its own way. They all do the same thing as before
> (increment/decrement a field), but AllocSet also subtracts out the free
> space in the current block. For Slab and Generation, we could do
> something similar, but it's not as much of a problem because there's no
> doubling of the allocation size.
>
> Although I think this still matches the word "allocation" in spirit,
> it's not technically correct, so feel free to suggest a new name for
> MemoryContextMemAllocated().

Procedurally, I think that it is highly inappropriate to submit a
patch two weeks after the start of the final CommitFest and then
commit it just over 48 hours later without a single endorsement of the
change from anyone.

Substantively, I think that whether or not this is improvement depends
considerably on how your OS handles overcommit. I do not have enough
knowledge to know whether it will be better in general, but would
welcome opinions from others.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company