Re: Using ProcSignal to get memory context stats from a running backend

On 2017-12-19 13:17:52 -0500, Tom Lane wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> > On Tue, Dec 19, 2017 at 8:44 AM, Craig Ringer <craig(at)2ndquadrant(dot)com> wrote:
> >> I didn't want to mess with the MemoryContextMethods and expose a
> >> printf-wrapper style typedef in memnodes.h, so I went with a hook global.
>
> > That looks pretty grotty to me. I think if you want to elog/ereport
> > this, you need to pass another argument to MemoryContextStats() or add
> > another memory context method. This is pretty much a textbook example
> > of the wrong way to use a global variable, IMHO.

Agreed.

> Yeah. But please don't mess with MemoryContextStats per se ---
> I dunno about you guys but "call MemoryContextStats(TopMemoryContext)"
> is kinda wired into my gdb reflexes. I think what'd make sense
> is a new function "MemoryContextStatsTo(context, function_pointer)".
> It's okay to redefine the APIs of the per-context-type functions
> these would call, though, because nobody calls those functions directly.

We already have MemoryContextStatsDetail() - it seems to make sense to
expand that API and leave MemoryContextStats() alone. I don't think
there's a need for a third variant?

Greetings,

Andres Freund