Refactor code in charge of grabbing the relations of a subscription

GetSubscriptionRelations() and GetSubscriptionNotReadyRelations() share
mostly the same code, which scans pg_subscription_rel and fetches all
the relations of a given subscription.  The only difference is that the
second routine looks for all the relations not in a ready state.  This
commit refactors the code to use a single routine, shaving a bit of
code.

Author: Vignesh C
Reviewed-By: Kyotaro Horiguchi, Amit Kapila, Michael Paquier, Peter
Smith
Discussion: https://postgr.es/m/CALDaNm0eW-9g4G_EzHebnFT5zZoasWCS_EzZQ5BgnLZny9S=pg@mail.gmail.com

src/backend/catalog/pg_subscription.c

@@ -533,65 +533,14 @@ HasSubscriptionRelations(Oid subid)
 }
 
 /*
- * Get all relations for subscription.
+ * Get the relations for the subscription.
  *
- * Returned list is palloc'ed in current memory context.
+ * If not_ready is true, return only the relations that are not in a ready
+ * state, otherwise return all the relations of the subscription.  The
+ * returned list is palloc'ed in the current memory context.
  */
 List *
-GetSubscriptionRelations(Oid subid)
+GetSubscriptionRelations(Oid subid, bool not_ready)
-{
-	List	   *res = NIL;
-	Relation	rel;
-	HeapTuple	tup;
-	ScanKeyData skey[1];
-	SysScanDesc scan;
-
-	rel = table_open(SubscriptionRelRelationId, AccessShareLock);
-
-	ScanKeyInit(&skey[0],
-				Anum_pg_subscription_rel_srsubid,
-				BTEqualStrategyNumber, F_OIDEQ,
-				ObjectIdGetDatum(subid));
-
-	scan = systable_beginscan(rel, InvalidOid, false,
-							  NULL, 1, skey);
-
-	while (HeapTupleIsValid(tup = systable_getnext(scan)))
-	{
-		Form_pg_subscription_rel subrel;
-		SubscriptionRelState *relstate;
-		Datum		d;
-		bool		isnull;
-
-		subrel = (Form_pg_subscription_rel) GETSTRUCT(tup);
-
-		relstate = (SubscriptionRelState *) palloc(sizeof(SubscriptionRelState));
-		relstate->relid = subrel->srrelid;
-		relstate->state = subrel->srsubstate;
-		d = SysCacheGetAttr(SUBSCRIPTIONRELMAP, tup,
-							Anum_pg_subscription_rel_srsublsn, &isnull);
-		if (isnull)
-			relstate->lsn = InvalidXLogRecPtr;
-		else
-			relstate->lsn = DatumGetLSN(d);
-
-		res = lappend(res, relstate);
-	}
-
-	/* Cleanup */
-	systable_endscan(scan);
-	table_close(rel, AccessShareLock);
-
-	return res;
-}
-
-/*
- * Get all relations for subscription that are not in a ready state.
- *
- * Returned list is palloc'ed in current memory context.
- */
-List *
-GetSubscriptionNotReadyRelations(Oid subid)
 {
 	List	   *res = NIL;
 	Relation	rel;
@@ -607,10 +556,11 @@ GetSubscriptionNotReadyRelations(Oid subid)
 				BTEqualStrategyNumber, F_OIDEQ,
 				ObjectIdGetDatum(subid));
 
-	ScanKeyInit(&skey[nkeys++],
+	if (not_ready)
-				Anum_pg_subscription_rel_srsubstate,
+		ScanKeyInit(&skey[nkeys++],
-				BTEqualStrategyNumber, F_CHARNE,
+					Anum_pg_subscription_rel_srsubstate,
-				CharGetDatum(SUBREL_STATE_READY));
+					BTEqualStrategyNumber, F_CHARNE,
+					CharGetDatum(SUBREL_STATE_READY));
 
 	scan = systable_beginscan(rel, InvalidOid, false,
 							  NULL, nkeys, skey);

src/backend/commands/subscriptioncmds.c

@@ -814,7 +814,7 @@ AlterSubscription_refresh(Subscription *sub, bool copy_data,
 		pubrel_names = fetch_table_list(wrconn, sub->publications);
 
 		/* Get local table list. */
-		subrel_states = GetSubscriptionRelations(sub->oid);
+		subrel_states = GetSubscriptionRelations(sub->oid, false);
 
 		/*
 		 * Build qsorted array of local table oids for faster lookup. This can
@@ -1494,7 +1494,7 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	 * the apply and tablesync workers and they can't restart because of
 	 * exclusive lock on the subscription.
 	 */
-	rstates = GetSubscriptionNotReadyRelations(subid);
+	rstates = GetSubscriptionRelations(subid, true);
 	foreach(lc, rstates)
 	{
 		SubscriptionRelState *rstate = (SubscriptionRelState *) lfirst(lc);

src/backend/replication/logical/tablesync.c

@@ -1479,7 +1479,7 @@ FetchTableStates(bool *started_tx)
 		}
 
 		/* Fetch all non-ready tables. */
-		rstates = GetSubscriptionNotReadyRelations(MySubscription->oid);
+		rstates = GetSubscriptionRelations(MySubscription->oid, true);
 
 		/* Allocate the tracking info in a permanent memory context. */
 		oldctx = MemoryContextSwitchTo(CacheMemoryContext);

src/include/catalog/pg_subscription_rel.h

@@ -88,7 +88,6 @@ extern char GetSubscriptionRelState(Oid subid, Oid relid, XLogRecPtr *sublsn);
 extern void RemoveSubscriptionRel(Oid subid, Oid relid);
 
 extern bool HasSubscriptionRelations(Oid subid);
-extern List *GetSubscriptionRelations(Oid subid);
+extern List *GetSubscriptionRelations(Oid subid, bool not_ready);
-extern List *GetSubscriptionNotReadyRelations(Oid subid);
 
 #endif							/* PG_SUBSCRIPTION_REL_H */