Set status for backend in background jobs

The status of background workers is recorded in PostgreSQL using the
function `pgstat_record_activity` which allow the status of the
background worker to be inspected using the `status` field in
`pg_stat_activity`.  This is used by the TimescaleDB `job_stats` view
to show if a job is running, scheduled, or paused.

However, the activity was never recorded in the code and hence the
field was always NULL. Since this was the default for the `job_status`
field of `timescaledb_information.job_stats` it would always show as
`Scheduled`.

This commit fixes this by adding calls to `pgstat_record_activity` at
suitable locations.

Fixes #2831

src/bgw/job_stat.c

@@ -429,6 +429,7 @@ ts_bgw_job_stat_mark_start(int32 bgw_job_id)
 									  RowExclusiveLock))
 			bgw_job_stat_insert_relation(rel, bgw_job_id, true, DT_NOBEGIN);
 		table_close(rel, ShareRowExclusiveLock);
+		pgstat_report_activity(STATE_IDLE, NULL);
 	}
 }
 
@@ -446,6 +447,7 @@ ts_bgw_job_stat_mark_end(BgwJob *job, JobResult result)
 								  &res,
 								  RowExclusiveLock))
 		elog(ERROR, "unable to find job statistics for job %d", job->fd.id);
+	pgstat_report_activity(STATE_IDLE, NULL);
 }
 
 bool

src/bgw/scheduler.c

@@ -734,6 +734,8 @@ ts_bgw_scheduler_process(int32 run_for_interval_ms,
 	TimestampTz start = ts_timer_get_current_timestamp();
 	TimestampTz quit_time = DT_NOEND;
 
+	pgstat_report_activity(STATE_RUNNING, NULL);
+
 	/* txn to read the list of jobs from the DB */
 	StartTransactionCommand();
 	scheduled_jobs = ts_update_scheduled_jobs_list(scheduled_jobs, scheduler_mctx);
@@ -763,7 +765,9 @@ ts_bgw_scheduler_process(int32 run_for_interval_ms,
 		next_wakeup = least_timestamp(next_wakeup, earliest_wakeup_to_start_next_job());
 		next_wakeup = least_timestamp(next_wakeup, earliest_job_timeout());
 
+		pgstat_report_activity(STATE_IDLE, NULL);
 		ts_timer_wait(next_wakeup);
+		pgstat_report_activity(STATE_RUNNING, NULL);
 
 		CHECK_FOR_INTERRUPTS();
 

tsl/src/bgw_policy/job.c

@@ -463,6 +463,7 @@ job_execute(BgwJob *job)
 	List *name;
 	FuncExpr *funcexpr;
 	MemoryContext parent_ctx = CurrentMemoryContext;
+	StringInfo query;
 
 	if (!IsTransactionOrTransactionBlock())
 	{
@@ -504,6 +505,19 @@ job_execute(BgwJob *job)
 							InvalidOid,
 							COERCE_EXPLICIT_CALL);
 
+	/* Here we create a query string from the function/procedure name that we
+	 * are calling. We do not update the status after the execution has
+	 * finished since this is wrapped inside the code that starts and stops
+	 * any job, not just custom jobs. We just provide more detailed
+	 * information here that we are actually calling a specific custom
+	 * function. */
+	query = makeStringInfo();
+	appendStringInfo(query,
+					 "CALL %s.%s()",
+					 quote_identifier(NameStr(job->fd.proc_schema)),
+					 quote_identifier(NameStr(job->fd.proc_name)));
+	pgstat_report_activity(STATE_RUNNING, query->data);
+
 	switch (prokind)
 	{
 		case PROKIND_FUNCTION:

tsl/test/expected/bgw_db_scheduler.out

@@ -212,6 +212,26 @@ SELECT application_name FROM pg_stat_activity WHERE application_name LIKE 'User-
  User-Defined Action [1001]
 (1 row)
 
+\x on
+SELECT job_id, job_status FROM timescaledb_information.job_stats;
+-[ RECORD 1 ]-------
+job_id     | 1001
+job_status | Running
+
+-- Showing non-volatile information from pg_stat_activity for
+-- debugging purposes. Information schema above reads from this view.
+SELECT datname, usename, application_name, state, query, wait_event_type, wait_event
+  FROM pg_stat_activity WHERE application_name LIKE 'User-Defined Action%';
+-[ RECORD 1 ]----+------------------------------------
+datname          | db_bgw_db_scheduler
+usename          | default_perm_user
+application_name | User-Defined Action [1001]
+state            | active
+query            | CALL public.ts_bgw_test_job_sleep()
+wait_event_type  | Timeout
+wait_event       | PgSleep
+
+\x off
 -- have to suppress notices here as delete_job will print pid of the running background worker processes
 SET client_min_messages TO WARNING;
 SELECT delete_job(:job_id);

tsl/test/sql/bgw_db_scheduler.sql

@@ -150,6 +150,14 @@ SELECT ts_bgw_db_scheduler_test_run();
 SELECT wait_for_logentry(:job_id);
 SELECT application_name FROM pg_stat_activity WHERE application_name LIKE 'User-Defined Action%';
 
+\x on
+SELECT job_id, job_status FROM timescaledb_information.job_stats;
+-- Showing non-volatile information from pg_stat_activity for
+-- debugging purposes. Information schema above reads from this view.
+SELECT datname, usename, application_name, state, query, wait_event_type, wait_event
+  FROM pg_stat_activity WHERE application_name LIKE 'User-Defined Action%';
+\x off
+
 -- have to suppress notices here as delete_job will print pid of the running background worker processes
 SET client_min_messages TO WARNING;
 SELECT delete_job(:job_id);