Re: Creating a function for exposing memory usage of backend process

On Fri, Aug 21, 2020 at 11:27:06PM +0900, torikoshia wrote:
> OK. Added a regression test on sysviews.sql.
> (0001-Added-a-regression-test-for-pg_backend_memory_contex.patch)
>
> Fujii-san gave us an example, but I added more simple one considering
> the simplicity of other tests on that.

What you have sent in 0001 looks fine to me. A small test is much
better than nothing.

> Added a patch for relocating the codes to mcxtfuncs.c.
> (patches/0001-Rellocated-the-codes-for-pg_backend_memory_contexts-.patch)

The same code is moved around line-by-line.

> Of course, this restriction makes pg_backend_memory_contexts hard to use
> when the user of the target session is not granted pg_monitor because the
> scope of this view is session local.
>
> In this case, I imagine additional operations something like temporarily
> granting pg_monitor to that user.

Hmm. I am not completely sure either that pg_monitor is the best fit
here, because this view provides information about a bunch of internal
structures. Something that could easily be done though is to revoke
the access from public, and then users could just set up GRANT
permissions post-initdb, with pg_monitor as one possible choice. This
is the safest path by default, and this stuff is of a caliber similar
to pg_shmem_allocations in terms of internal contents.

It seems to me that you are missing one "REVOKE ALL on
pg_backend_memory_contexts FROM PUBLIC" in patch 0003.

By the way, if that was just for me, I would remove used_bytes, which
is just a computation from the total and free numbers. I'll defer
that point to Fujii-san.
--
Michael