PL instrumentation plugin and Rendezvous variable support - version 2

This is an updated version of the PL instrumentation plugin patch that I
submitted on July-28. The new version re-implements the plugin loader
code to use "rendezvous variables" as suggested by Tom Lane (thanks Tom,
very elegant design).

I have not implemented any support for unloading shared libraries. Once
we've finalized the design for rendezvous variables, I'll submit a
separate documentation patch.

-- Korry

--
Korry Douglas korryd(at)enterprisedb(dot)com
EnterpriseDB http://www.enterprisedb.com

"korryd(at)enterprisedb(dot)com" <korryd(at)enterprisedb(dot)com> writes:
> This is an updated version of the PL instrumentation plugin patch that I
> submitted on July-28. The new version re-implements the plugin loader
> code to use "rendezvous variables" as suggested by Tom Lane (thanks Tom,
> very elegant design).

Applied with a few small changes --- I renamed the GUC variables after a
suggestion by Simon Riggs, and fixed things so that
backend_load_libraries could actually do something useful (you had it as
PGC_POSTMASTER, making it effectively no more flexible than the existing
preload_libraries list).

The only change that will directly impact your code is that I thought
it'd be better to provide plpgsql_exec_error_callback and
exec_assign_expr as separate fields instead of arguments to func_setup,
viz

if (*plugin_ptr)
{
(*plugin_ptr)->error_callback = plpgsql_exec_error_callback;
(*plugin_ptr)->assign_expr = exec_assign_expr;

if ((*plugin_ptr)->func_setup)
((*plugin_ptr)->func_setup)(estate, func);
}

I'm not totally wedded to this if you don't like it, but my thought was
that passing these as arguments to func_setup would mean a lot of pain
anytime we wanted to change the set of function pointers provided:
every plugin would need textual changes whether it actually used these
functions or not.

> I have not implemented any support for unloading shared libraries. Once
> we've finalized the design for rendezvous variables, I'll submit a
> separate documentation patch.

I added docs for the GUC variables but didn't do more than that. I
think the code comments are probably sufficient as far as rendezvous
variables and PLpgSQL_plugin go ... did you have something else in mind?

regards, tom lane

> Applied with a few small changes --- I renamed the GUC variables after a
> suggestion by Simon Riggs, and fixed things so that
> backend_load_libraries could actually do something useful (you had it as
> PGC_POSTMASTER, making it effectively no more flexible than the existing
> preload_libraries list).

'Doh! That was a cut/paste error on my part. Thanks.

> The only change that will directly impact your code is that I thought
> it'd be better to provide plpgsql_exec_error_callback and
> exec_assign_expr as separate fields instead of arguments to func_setup,
> viz
>
> if (*plugin_ptr)
> {
> (*plugin_ptr)->error_callback = plpgsql_exec_error_callback;
> (*plugin_ptr)->assign_expr = exec_assign_expr;
>
> if ((*plugin_ptr)->func_setup)
> ((*plugin_ptr)->func_setup)(estate, func);
> }
>
> I'm not totally wedded to this if you don't like it, but my thought was
> that passing these as arguments to func_setup would mean a lot of pain
> anytime we wanted to change the set of function pointers provided:
> every plugin would need textual changes whether it actually used these
> functions or not.

Good idea, those two function pointers are sort of necessary-evil
required only by the debugger plugin (other plugins presumably won't
need them).

> > I have not implemented any support for unloading shared libraries. Once
> > we've finalized the design for rendezvous variables, I'll submit a
> > separate documentation patch.
>
> I added docs for the GUC variables but didn't do more than that. I
> think the code comments are probably sufficient as far as rendezvous
> variables and PLpgSQL_plugin go ... did you have something else in mind?

I'll look around the existing documentation to see if I can find an
appropriate place, but we don't really have an implementor's guide.

Thanks for your help and suggestions.

-- Korry

--
Korry Douglas korryd(at)enterprisedb(dot)com
EnterpriseDB http://www.enterprisedb.com