Re: RFC: replace pg_stat_activity.waiting with something more descriptive

On 08/04/2015 03:15 PM, Robert Haas wrote:
> On Tue, Jul 28, 2015 at 3:28 PM, Heikki Linnakangas <hlinnaka(at)iki(dot)fi> wrote:
>> * The patch requires that the LWLOCK_INDIVIDUAL_NAMES array is kept in sync
>> with the list of individual locks in lwlock.h. Sooner or later someone will
>> add an LWLock and forget to update the names-array. That needs to be made
>> less error-prone, so that the names are maintained in the same place as the
>> #defines. Perhaps something like rmgrlist.h.
>
> This is a good idea, but it's not easy to do in the style of
> rmgrlist.h, because I don't believe there's any way to define a macro
> that expands to a preprocessor directive. Attached is a patch that
> instead generates the list of macros from a text file, and also
> generates an array inside lwlock.c with the lock names that gets used
> by the Trace_lwlocks stuff where applicable.
>
> Any objections to this solution to the problem? If not, I'd like to
> go ahead and push this much. I can't test the Windows changes
> locally, though, so it would be helpful if someone could check that
> out.

A more low-tech solution would be to something like this in lwlocknames.c:

static char *MainLWLockNames[NUM_INDIVIDUAL_LWLOCKS];

/* Turn pointer into one of the LWLocks in main array into an index
number */
#define NAME_LWLOCK(l, name) MainLWLockNames[l - MainLWLockArray)] = name

InitLWLockNames()
{
NAME_LWLOCK(ShmemIndexLock, "ShmemIndexLock");
NAME_LWLOCK(OidGenLock, "OidGenLock");
...
}

That would not be auto-generated, so you'd need to keep that list in
sync with lwlock.h, but it would be much better than the original patch
because if you forgot to add an entry in the names-array, the numbering
of all the other locks would not go wrong. And you could have a runtime
check that complains if there's an entry missing, like Ildus did in his
latest patch.

I have no particular objection to your perl script either, though. I'll
leave it up to you.

- Heikki