Re: stored procedure stats in collector

Howdy,

Here's an updated version of the function stats patch. The biggest change is
that by default only procedural language functions are counted. The GUC variable
stats_function_level now takes 3 values: on, off and all. The latter also
counts SQL and C language functions, "on" means only to count procedural
language functions. The decision is now made in fmgr_info_cxt_security()
Trigger functions are now also counted.

Sample output:

select procname, calls, total_time, total_cpu, self_time, self_cpu
from pg_stat_user_functions order by self_cpu desc limit 5;

       procname      | calls | total_time | total_cpu | self_time | self_cpu
--------------------+-------+------------+-----------+-----------+----------
  next_batch         | 32765 |      27139 |      8574 |     27139 |     8574
  fetch_batch_events |  3636 |       9252 |      5622 |      3771 |     2717
  batch_event_sql    |  3636 |       5454 |      2888 |      3910 |     1962
  finish_batch       |  3420 |       3215 |      1475 |      3215 |     1475
  batch_event_tables |  3636 |       1448 |       865 |      1434 |      858
(5 rows)

This is still 8.2 only (tested on 8.2.4 and 8.2.5), has seen some production
usage here at Skype (about a month on reasonably busy boxes). So far so good.

Couple of issues:
- sometimes self_cpu > self_time - currently blaming it on Linux version of
gettimeofday().
- dropped functions are not purged from stats, might bloat the stats file for
some usage patterns.

PS. Would something like this be a canditate for 8.4 inclusion (if polished up)?

Regards,
Martin