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

On 2020-08-24 13:13, Fujii Masao wrote:
> On 2020/08/24 13:01, torikoshia wrote:
>> On 2020-08-22 21:18, Michael Paquier wrote:
>> 
>> Thanks for reviewing!
>> 
>>> 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.
> 
> +1
> 
> But as I proposed upthread, what about a bit complicated test as 
> follows,
> e.g., to confirm that the internal logic for level works expectedly?
> 
>      SELECT name, ident, parent, level, total_bytes >= free_bytes FROM
> pg_backend_memory_contexts WHERE level = 0;

OK!
Attached an updated patch.

> 
> 
>>> 
>>>> Added a patch for relocating the codes to mcxtfuncs.c.
>>>> (patches/0001-Rellocated-the-codes-for-pg_backend_memory_contexts-.patch)
> 
> Thanks for the patch! Looks good to me.
> Barring any objection, I will commit this patch at first.
> 
> 
>>> 
>>> 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.
>> 
>> I think this is a better way than what I did in
>> 0001-Rellocated-the-codes-for-pg_backend_memory_contexts-.patch.
> 
> You mean 
> 0001-Restrict-the-access-to-pg_backend_memory_contexts-to.patch?

Oops, I meant 
0001-Restrict-the-access-to-pg_backend_memory_contexts-to.patch.

> 
> 
>> Attached a patch.
> 
> Thanks for updating the patch! This also looks good to me.
> 
> 
>>> 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.
> 
> Yeah, I was just thinking that displaying also used_bytes was useful,
> but this might be inconsistent with the other views' ways.
> 
> Regards,

Regards,

--
Atsushi Torikoshi
NTT DATA CORPORATION