More precise errors from initial pg_control check

Use a separate error message for invalid checkpoint location and
invalid state instead of just "invalid data" for both.
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://www.postgresql.org/message-id/20191107041630.GK1768@paquier.xyz

src/backend/access/transam/xlog.c

@@ -6231,45 +6231,59 @@ StartupXLOG(void)
 	CurrentResourceOwner = AuxProcessResourceOwner;
 
 	/*
-	 * Verify XLOG status looks valid.
+	 * Check that contents look valid.
 	 */
-	if (ControlFile->state < DB_SHUTDOWNED ||
-		ControlFile->state > DB_IN_PRODUCTION ||
-		!XRecOffIsValid(ControlFile->checkPoint))
+	if (!XRecOffIsValid(ControlFile->checkPoint))
 		ereport(FATAL,
-				(errmsg("control file contains invalid data")));
+				(errmsg("control file contains invalid checkpoint location")));
 
-	if (ControlFile->state == DB_SHUTDOWNED)
+	switch (ControlFile->state)
 	{
-		/* This is the expected case, so don't be chatty in standalone mode */
-		ereport(IsPostmasterEnvironment ? LOG : NOTICE,
-				(errmsg("database system was shut down at %s",
-						str_time(ControlFile->time))));
+		case DB_SHUTDOWNED:
+			/* This is the expected case, so don't be chatty in standalone mode */
+			ereport(IsPostmasterEnvironment ? LOG : NOTICE,
+					(errmsg("database system was shut down at %s",
+							str_time(ControlFile->time))));
+			break;
+
+		case DB_SHUTDOWNED_IN_RECOVERY:
+			ereport(LOG,
+					(errmsg("database system was shut down in recovery at %s",
+							str_time(ControlFile->time))));
+			break;
+
+		case DB_SHUTDOWNING:
+			ereport(LOG,
+					(errmsg("database system shutdown was interrupted; last known up at %s",
+							str_time(ControlFile->time))));
+			break;
+
+		case DB_IN_CRASH_RECOVERY:
+			ereport(LOG,
+					(errmsg("database system was interrupted while in recovery at %s",
+							str_time(ControlFile->time)),
+					 errhint("This probably means that some data is corrupted and"
+							 " you will have to use the last backup for recovery.")));
+			break;
+
+		case DB_IN_ARCHIVE_RECOVERY:
+			ereport(LOG,
+					(errmsg("database system was interrupted while in recovery at log time %s",
+							str_time(ControlFile->checkPointCopy.time)),
+					 errhint("If this has occurred more than once some data might be corrupted"
+							 " and you might need to choose an earlier recovery target.")));
+			break;
+
+		case DB_IN_PRODUCTION:
+			ereport(LOG,
+					(errmsg("database system was interrupted; last known up at %s",
+							str_time(ControlFile->time))));
+			break;
+
+		default:
+			ereport(FATAL,
+					(errmsg("control file contains invalid database cluster state")));
 	}
-	else if (ControlFile->state == DB_SHUTDOWNED_IN_RECOVERY)
-		ereport(LOG,
-				(errmsg("database system was shut down in recovery at %s",
-						str_time(ControlFile->time))));
-	else if (ControlFile->state == DB_SHUTDOWNING)
-		ereport(LOG,
-				(errmsg("database system shutdown was interrupted; last known up at %s",
-						str_time(ControlFile->time))));
-	else if (ControlFile->state == DB_IN_CRASH_RECOVERY)
-		ereport(LOG,
-				(errmsg("database system was interrupted while in recovery at %s",
-						str_time(ControlFile->time)),
-				 errhint("This probably means that some data is corrupted and"
-						 " you will have to use the last backup for recovery.")));
-	else if (ControlFile->state == DB_IN_ARCHIVE_RECOVERY)
-		ereport(LOG,
-				(errmsg("database system was interrupted while in recovery at log time %s",
-						str_time(ControlFile->checkPointCopy.time)),
-				 errhint("If this has occurred more than once some data might be corrupted"
-						 " and you might need to choose an earlier recovery target.")));
-	else if (ControlFile->state == DB_IN_PRODUCTION)
-		ereport(LOG,
-				(errmsg("database system was interrupted; last known up at %s",
-						str_time(ControlFile->time))));
 
 	/* This is just to allow attaching to startup process with a debugger */
 #ifdef XLOG_REPLAY_DELAY