Re: [HACKERS] exposing wait events for non-backends (was: Trackingwait event for latches)

Hello everyone,

As discussed in this thread, I've attached a set of patches to show
auxiliary processes, autovacuum launcher and bgworker along with other
backends in pg_stat_activity. For now, I've extended
BackendStatusArray to store auxiliary processes. Backends use slots
indexed in the range from 1 to MaxBackends (inclusive), so we use
MaxBackends + AuxProcType + 1 as the index of the slot for an
auxiliary process. However, BackendStatusArray should be renamed to
something like 'ProcStatusArray' along with many others in pgstat.c
and pgstatfuncs.c(Ex: LocalPgBackendStatus etc). But, that needs a
major code refactoring. I can do the changes if we agree with that.

I've also kept a local array, named localBackendStatusIndex, which
stores the index of currently active backends from BackendStatusArray.
It assigns ids to currently active backend from 1 to the number of
active backends.(It is required in some pgstat_* functions, for
example: pg_stat_get_backend_idset). Hence, we are not affecting the
outputs of other sql functions apart from pg_stat_activity and
pg_stat_get_activity.

I've also added an extra column, named proc_type (suggested by Craig
and Robert), to indicate the type of process in pg_stat_activity view.
proc_type includes:

* client backend
* autovacuum launcher
* wal sender
* bgworker
* writer
* checkpointer
* wal writer
* wal receiver

Here is the present output with the relevant columns. (Didn't show
backend_start since it takes too long space)

postgres=# select pid, usesysid, application_name, wait_event_type,
wait_event, state, proc_type from pg_stat_activity;
  pid   | usesysid |       application_name       | wait_event_type |
   wait_event      | state  |      proc_type

--------+----------+------------------------------+-----------------+---------------------+--------+---------------------
 109945 |          |                              | Activity        |
AutoVacuumMain      | idle   | autovacuum launcher
 109947 |          | logical replication launcher | Activity        |
LogicalLauncherMain | idle   | bgworker
 109962 |       10 | walreceiver                  | Activity        |
WalSenderMain       | idle   | wal sender
 109976 |       10 | psql                         |                 |
                   | active | client backend
 109943 |          |                              | Activity        |
BgWriterMain        | idle   | writer
 109942 |          |                              | Activity        |
CheckpointerMain    | idle   | checkpointer
 109944 |          |                              | Activity        |
WalWriterMain       | idle   | wal writer
(7 rows)

Whereas, the output of other pgstat_* functions remains unchanged. For example,

postgres=# SELECT pg_stat_get_backend_pid(s.backendid) AS procpid,
       pg_stat_get_backend_activity(s.backendid) AS current_query
    FROM (SELECT pg_stat_get_backend_idset() AS backendid) AS s;
 procpid |                           current_query
---------+-------------------------------------------------------------------
  120713 | SELECT pg_stat_get_backend_pid(s.backendid) AS procpid,          +
         |        pg_stat_get_backend_activity(s.backendid) AS current_query+
         |     FROM (SELECT pg_stat_get_backend_idset() AS backendid) AS s;


Thoughts?

-- 
Thanks & Regards,
Kuntal Ghosh
EnterpriseDB: http://www.enterprisedb.com

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