Simplify determining logical replication worker types.

We deduce a LogicalRepWorker's type from the values of several different
fields ('relid' and 'leader_pid') whenever logic needs to know it.

In fact, the logical replication worker type is already known at the time
of launching the LogicalRepWorker and it never changes for the lifetime of
that process. Instead of deducing the type, it is simpler to just store it
one time, and access it directly thereafter.

Author: Peter Smith
Reviewed-by: Amit Kapila, Bharath Rupireddy
Discussion: http://postgr.es/m/CAHut+PttPSuP0yoZ=9zLDXKqTJ=d0bhxwKaEaNcaym1XqcvDEg@mail.gmail.com

src/backend/replication/logical/applyparallelworker.c

@@ -435,7 +435,8 @@ pa_launch_parallel_worker(void)
 		return NULL;
 	}
 
-	launched = logicalrep_worker_launch(MyLogicalRepWorker->dbid,
+	launched = logicalrep_worker_launch(WORKERTYPE_PARALLEL_APPLY,
+										MyLogicalRepWorker->dbid,
 										MySubscription->oid,
 										MySubscription->name,
 										MyLogicalRepWorker->userid,

src/backend/replication/logical/launcher.c

@@ -303,7 +303,8 @@ logicalrep_workers_find(Oid subid, bool only_running)
  * Returns true on success, false on failure.
  */
 bool
-logicalrep_worker_launch(Oid dbid, Oid subid, const char *subname, Oid userid,
+logicalrep_worker_launch(LogicalRepWorkerType wtype,
+						 Oid dbid, Oid subid, const char *subname, Oid userid,
 						 Oid relid, dsm_handle subworker_dsm)
 {
 	BackgroundWorker bgw;
@@ -315,10 +316,18 @@ logicalrep_worker_launch(Oid dbid, Oid subid, const char *subname, Oid userid,
 	int			nsyncworkers;
 	int			nparallelapplyworkers;
 	TimestampTz now;
-	bool		is_parallel_apply_worker = (subworker_dsm != DSM_HANDLE_INVALID);
+	bool		is_tablesync_worker = (wtype == WORKERTYPE_TABLESYNC);
+	bool		is_parallel_apply_worker = (wtype == WORKERTYPE_PARALLEL_APPLY);
 
-	/* Sanity check - tablesync worker cannot be a subworker */
-	Assert(!(is_parallel_apply_worker && OidIsValid(relid)));
+	/*----------
+	 * Sanity checks:
+	 * - must be valid worker type
+	 * - tablesync workers are only ones to have relid
+	 * - parallel apply worker is the only kind of subworker
+	 */
+	Assert(wtype != WORKERTYPE_UNKNOWN);
+	Assert(is_tablesync_worker == OidIsValid(relid));
+	Assert(is_parallel_apply_worker == (subworker_dsm != DSM_HANDLE_INVALID));
 
 	ereport(DEBUG1,
 			(errmsg_internal("starting logical replication worker for subscription \"%s\"",
@@ -393,7 +402,7 @@ retry:
 	 * sync worker limit per subscription. So, just return silently as we
 	 * might get here because of an otherwise harmless race condition.
 	 */
-	if (OidIsValid(relid) && nsyncworkers >= max_sync_workers_per_subscription)
+	if (is_tablesync_worker && nsyncworkers >= max_sync_workers_per_subscription)
 	{
 		LWLockRelease(LogicalRepWorkerLock);
 		return false;
@@ -427,6 +436,7 @@ retry:
 	}
 
 	/* Prepare the worker slot. */
+	worker->type = wtype;
 	worker->launch_time = now;
 	worker->in_use = true;
 	worker->generation++;
@@ -466,7 +476,7 @@ retry:
 				 subid);
 		snprintf(bgw.bgw_type, BGW_MAXLEN, "logical replication parallel worker");
 	}
-	else if (OidIsValid(relid))
+	else if (is_tablesync_worker)
 	{
 		snprintf(bgw.bgw_function_name, BGW_MAXLEN, "TablesyncWorkerMain");
 		snprintf(bgw.bgw_name, BGW_MAXLEN,
@@ -847,7 +857,7 @@ logicalrep_sync_worker_count(Oid subid)
 	{
 		LogicalRepWorker *w = &LogicalRepCtx->workers[i];
 
-		if (w->subid == subid && OidIsValid(w->relid))
+		if (w->subid == subid && isTablesyncWorker(w))
 			res++;
 	}
 
@@ -1180,7 +1190,8 @@ ApplyLauncherMain(Datum main_arg)
 				(elapsed = TimestampDifferenceMilliseconds(last_start, now)) >= wal_retrieve_retry_interval)
 			{
 				ApplyLauncherSetWorkerStartTime(sub->oid, now);
-				logicalrep_worker_launch(sub->dbid, sub->oid, sub->name,
+				logicalrep_worker_launch(WORKERTYPE_APPLY,
+										 sub->dbid, sub->oid, sub->name,
 										 sub->owner, InvalidOid,
 										 DSM_HANDLE_INVALID);
 			}
@@ -1290,7 +1301,7 @@ pg_stat_get_subscription(PG_FUNCTION_ARGS)
 		worker_pid = worker.proc->pid;
 
 		values[0] = ObjectIdGetDatum(worker.subid);
-		if (OidIsValid(worker.relid))
+		if (isTablesyncWorker(&worker))
 			values[1] = ObjectIdGetDatum(worker.relid);
 		else
 			nulls[1] = true;

src/backend/replication/logical/tablesync.c

@@ -587,7 +587,8 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
 						TimestampDifferenceExceeds(hentry->last_start_time, now,
 												   wal_retrieve_retry_interval))
 					{
-						logicalrep_worker_launch(MyLogicalRepWorker->dbid,
+						logicalrep_worker_launch(WORKERTYPE_TABLESYNC,
+												 MyLogicalRepWorker->dbid,
 												 MySubscription->oid,
 												 MySubscription->name,
 												 MyLogicalRepWorker->userid,

src/include/replication/worker_internal.h

@@ -27,9 +27,20 @@
 #include "storage/shm_toc.h"
 #include "storage/spin.h"
 
+/* Different types of worker */
+typedef enum LogicalRepWorkerType
+{
+	WORKERTYPE_UNKNOWN = 0,
+	WORKERTYPE_TABLESYNC,
+	WORKERTYPE_APPLY,
+	WORKERTYPE_PARALLEL_APPLY
+} LogicalRepWorkerType;
 
 typedef struct LogicalRepWorker
 {
+	/* What type of worker is this? */
+	LogicalRepWorkerType type;
+
 	/* Time at which this worker was launched. */
 	TimestampTz launch_time;
 
@@ -232,7 +243,8 @@ extern void logicalrep_worker_attach(int slot);
 extern LogicalRepWorker *logicalrep_worker_find(Oid subid, Oid relid,
 												bool only_running);
 extern List *logicalrep_workers_find(Oid subid, bool only_running);
-extern bool logicalrep_worker_launch(Oid dbid, Oid subid, const char *subname,
+extern bool logicalrep_worker_launch(LogicalRepWorkerType wtype,
+									 Oid dbid, Oid subid, const char *subname,
 									 Oid userid, Oid relid,
 									 dsm_handle subworker_dsm);
 extern void logicalrep_worker_stop(Oid subid, Oid relid);
@@ -315,19 +327,19 @@ extern void pa_decr_and_wait_stream_block(void);
 extern void pa_xact_finish(ParallelApplyWorkerInfo *winfo,
 						   XLogRecPtr remote_lsn);
 
-#define isParallelApplyWorker(worker) ((worker)->leader_pid != InvalidPid)
+#define isParallelApplyWorker(worker) ((worker)->type == WORKERTYPE_PARALLEL_APPLY)
+#define isTablesyncWorker(worker) ((worker)->type == WORKERTYPE_TABLESYNC)
 
 static inline bool
 am_tablesync_worker(void)
 {
-	return OidIsValid(MyLogicalRepWorker->relid);
+	return isTablesyncWorker(MyLogicalRepWorker);
 }
 
 static inline bool
 am_leader_apply_worker(void)
 {
-	return (!am_tablesync_worker() &&
-			!isParallelApplyWorker(MyLogicalRepWorker));
+	return (MyLogicalRepWorker->type == WORKERTYPE_APPLY);
 }
 
 static inline bool

src/tools/pgindent/typedefs.list

@@ -1500,6 +1500,7 @@ LogicalRepStreamAbortData
 LogicalRepTupleData
 LogicalRepTyp
 LogicalRepWorker
+LogicalRepWorkerType
 LogicalRewriteMappingData
 LogicalTape
 LogicalTapeSet