Fix statistics reporting in logical replication workers

This new arrangement ensures that statistics are reported right after
commit of transactions.  The previous arrangement didn't get this quite
right and could lead to assertion failures.

Author: Petr Jelinek <petr.jelinek@2ndquadrant.com>
Reported-by: Erik Rijkers <er@xs4all.nl>

src/backend/replication/logical/tablesync.c

@@ -274,6 +274,7 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
 	static List *table_states = NIL;
 	static HTAB *last_start_times = NULL;
 	ListCell   *lc;
+	bool		started_tx = false;
 
 	Assert(!IsTransactionState());
 
@@ -290,6 +291,7 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
 		table_states = NIL;
 
 		StartTransactionCommand();
+		started_tx = true;
 
 		/* Fetch all non-ready tables. */
 		rstates	= GetSubscriptionNotReadyRelations(MySubscription->oid);
@@ -304,8 +306,6 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
 		}
 		MemoryContextSwitchTo(oldctx);
 
-		CommitTransactionCommand();
-
 		table_states_valid = true;
 	}
 
@@ -350,11 +350,14 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
 			{
 				rstate->state = SUBREL_STATE_READY;
 				rstate->lsn = current_lsn;
-				StartTransactionCommand();
+				if (!started_tx)
+				{
+					StartTransactionCommand();
+					started_tx = true;
+				}
 				SetSubscriptionRelState(MyLogicalRepWorker->subid,
 										rstate->relid, rstate->state,
 										rstate->lsn);
-				CommitTransactionCommand();
 			}
 		}
 		else
@@ -457,6 +460,12 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
 			}
 		}
 	}
+
+	if (started_tx)
+	{
+		CommitTransactionCommand();
+		pgstat_report_stat(false);
+	}
 }
 
 /*
@@ -806,6 +815,7 @@ LogicalRepSyncTableStart(XLogRecPtr *origin_startpos)
 										MyLogicalRepWorker->relstate,
 										MyLogicalRepWorker->relstate_lsn);
 				CommitTransactionCommand();
+				pgstat_report_stat(false);
 
 				/*
 				 * We want to do the table data sync in single

src/backend/replication/logical/worker.c

@@ -453,6 +453,7 @@ apply_handle_commit(StringInfo s)
 		replorigin_session_origin_timestamp = commit_data.committime;
 
 		CommitTransactionCommand();
+		pgstat_report_stat(false);
 
 		store_flush_position(commit_data.end_lsn);
 	}
@@ -462,7 +463,6 @@ apply_handle_commit(StringInfo s)
 	/* Process any tables that are being synchronized in parallel. */
 	process_syncing_tables(commit_data.end_lsn);
 
-	pgstat_report_stat(false);
 	pgstat_report_activity(STATE_IDLE, NULL);
 }