Improve ERROR/LOG messages added by commits ddd5f4f and 7a424ec.

Additionally, in slotsync.c, replace one StringInfoData variable usage
with a constant string to avoid palloc/pfree. Also, replace the inclusion
of "logical.h" with "slot.h" to prevent the exposure of unnecessary
implementation details.

Reported-by: Kyotaro Horiguchi, Masahiko Sawada
Author: Shveta Malik based on suggestions by Robert Haas and Amit Kapila
Reviewed-by: Kyotaro Horiguchi, Amit Kapila
Discussion: https://postgr.es/m/20240214.162652.773291409747353211.horikyota.ntt@gmail.com
Discussion: https://postgr.es/m/20240219.134015.1888940527023074780.horikyota.ntt@gmail.com
Discussion: https://postgr.es/m/CAD21AoCYXhDYOQDAS-rhGasC2T+tYbV=8Y18o94sB=5AxcW+yA@mail.gmail.com

Author: Amit Kapila

src/backend/replication/logical/slotsync.c

@@ -35,7 +35,7 @@
 #include "access/xlogrecovery.h"
 #include "catalog/pg_database.h"
 #include "commands/dbcommands.h"
-#include "replication/logical.h"
+#include "replication/slot.h"
 #include "replication/slotsync.h"
 #include "storage/ipc.h"
 #include "storage/lmgr.h"
@@ -368,14 +368,13 @@ update_and_persist_local_synced_slot(RemoteSlot *remote_slot, Oid remote_dbid)
 		 * XXX should this be changed to elog(DEBUG1) perhaps?
 		 */
 		ereport(LOG,
-				errmsg("could not sync slot information as remote slot precedes local slot:"
-					   " remote slot \"%s\": LSN (%X/%X), catalog xmin (%u) local slot: LSN (%X/%X), catalog xmin (%u)",
-					   remote_slot->name,
-					   LSN_FORMAT_ARGS(remote_slot->restart_lsn),
-					   remote_slot->catalog_xmin,
-					   LSN_FORMAT_ARGS(slot->data.restart_lsn),
-					   slot->data.catalog_xmin));
-
+				errmsg("could not sync slot \"%s\" as remote slot precedes local slot",
+					   remote_slot->name),
+				errdetail("Remote slot has LSN %X/%X and catalog xmin %u, but local slot has LSN %X/%X and catalog xmin %u.",
+						  LSN_FORMAT_ARGS(remote_slot->restart_lsn),
+						  remote_slot->catalog_xmin,
+						  LSN_FORMAT_ARGS(slot->data.restart_lsn),
+						  slot->data.catalog_xmin));
 		return;
 	}
 
@@ -569,8 +568,12 @@ synchronize_slots(WalReceiverConn *wrconn)
 
 	WalRcvExecResult *res;
 	TupleTableSlot *tupslot;
-	StringInfoData s;
 	List	   *remote_slot_list = NIL;
+	const char *query = "SELECT slot_name, plugin, confirmed_flush_lsn,"
+		" restart_lsn, catalog_xmin, two_phase, failover,"
+		" database, conflict_reason"
+		" FROM pg_catalog.pg_replication_slots"
+		" WHERE failover and NOT temporary";
 
 	SpinLockAcquire(&SlotSyncCtx->mutex);
 	if (SlotSyncCtx->syncing)
@@ -586,19 +589,8 @@ synchronize_slots(WalReceiverConn *wrconn)
 
 	syncing_slots = true;
 
-	initStringInfo(&s);
-
-	/* Construct query to fetch slots with failover enabled. */
-	appendStringInfo(&s,
-					 "SELECT slot_name, plugin, confirmed_flush_lsn,"
-					 " restart_lsn, catalog_xmin, two_phase, failover,"
-					 " database, conflict_reason"
-					 " FROM pg_catalog.pg_replication_slots"
-					 " WHERE failover and NOT temporary");
-
 	/* Execute the query */
-	res = walrcv_exec(wrconn, s.data, SLOTSYNC_COLUMN_COUNT, slotRow);
-	pfree(s.data);
+	res = walrcv_exec(wrconn, query, SLOTSYNC_COLUMN_COUNT, slotRow);
 
 	if (res->status != WALRCV_OK_TUPLES)
 		ereport(ERROR,
@@ -743,12 +735,12 @@ validate_remote_info(WalReceiverConn *wrconn)
 		ereport(ERROR,
 				errmsg("could not fetch primary_slot_name \"%s\" info from the primary server: %s",
 					   PrimarySlotName, res->err),
-				errhint("Check if \"primary_slot_name\" is configured correctly."));
+				errhint("Check if primary_slot_name is configured correctly."));
 
 	tupslot = MakeSingleTupleTableSlot(res->tupledesc, &TTSOpsMinimalTuple);
 	if (!tuplestore_gettupleslot(res->tuplestore, true, false, tupslot))
 		elog(ERROR,
-			 "failed to fetch tuple for the primary server slot specified by \"primary_slot_name\"");
+			 "failed to fetch tuple for the primary server slot specified by primary_slot_name");
 
 	remote_in_recovery = DatumGetBool(slot_getattr(tupslot, 1, &isnull));
 	Assert(!isnull);
@@ -764,9 +756,9 @@ validate_remote_info(WalReceiverConn *wrconn)
 	if (!primary_slot_valid)
 		ereport(ERROR,
 				errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-				errmsg("bad configuration for slot synchronization"),
+				errmsg("slot synchronization requires valid primary_slot_name"),
 		/* translator: second %s is a GUC variable name */
-				errdetail("The replication slot \"%s\" specified by \"%s\" does not exist on the primary server.",
+				errdetail("The replication slot \"%s\" specified by %s does not exist on the primary server.",
 						  PrimarySlotName, "primary_slot_name"));
 
 	ExecClearTuple(tupslot);
@@ -792,8 +784,7 @@ ValidateSlotSyncParams(void)
 		ereport(ERROR,
 		/* translator: %s is a GUC variable name */
 				errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-				errmsg("bad configuration for slot synchronization"),
-				errhint("\"%s\" must be defined.", "primary_slot_name"));
+				errmsg("slot synchronization requires %s to be defined", "primary_slot_name"));
 
 	/*
 	 * hot_standby_feedback must be enabled to cooperate with the physical
@@ -804,15 +795,14 @@ ValidateSlotSyncParams(void)
 		ereport(ERROR,
 		/* translator: %s is a GUC variable name */
 				errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-				errmsg("bad configuration for slot synchronization"),
-				errhint("\"%s\" must be enabled.", "hot_standby_feedback"));
+				errmsg("slot synchronization requires %s to be enabled",
+					   "hot_standby_feedback"));
 
 	/* Logical slot sync/creation requires wal_level >= logical. */
 	if (wal_level < WAL_LEVEL_LOGICAL)
 		ereport(ERROR,
 				errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-				errmsg("bad configuration for slot synchronization"),
-				errhint("\"wal_level\" must be >= logical."));
+				errmsg("slot synchronization requires wal_level >= \"logical\""));
 
 	/*
 	 * The primary_conninfo is required to make connection to primary for
@@ -822,8 +812,8 @@ ValidateSlotSyncParams(void)
 		ereport(ERROR,
 		/* translator: %s is a GUC variable name */
 				errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-				errmsg("bad configuration for slot synchronization"),
-				errhint("\"%s\" must be defined.", "primary_conninfo"));
+				errmsg("slot synchronization requires %s to be defined",
+					   "primary_conninfo"));
 
 	/*
 	 * The slot synchronization needs a database connection for walrcv_exec to
@@ -834,12 +824,11 @@ ValidateSlotSyncParams(void)
 		ereport(ERROR,
 
 		/*
-		 * translator: 'dbname' is a specific option; %s is a GUC variable
-		 * name
+		 * translator: dbname is a specific option; %s is a GUC variable name
 		 */
 				errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-				errmsg("bad configuration for slot synchronization"),
-				errhint("'dbname' must be specified in \"%s\".", "primary_conninfo"));
+				errmsg("slot synchronization requires dbname to be specified in %s",
+					   "primary_conninfo"));
 }
 
 /*

src/test/recovery/t/040_standby_failover_slots_sync.pl

@@ -319,7 +319,7 @@
 ($result, $stdout, $stderr) =
   $standby1->psql('postgres', "SELECT pg_sync_replication_slots();");
 ok( $stderr =~
-	  /HINT:  'dbname' must be specified in "primary_conninfo"/,
+	  /ERROR:  slot synchronization requires dbname to be specified in primary_conninfo/,
 	"cannot sync slots if dbname is not specified in primary_conninfo");
 
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