DISTMYSQL-396: Fix for DISTMYSQL-243 can lead to Orchestrator hitting duplicate keys

https://perconadev.atlassian.net/browse/DISTMYSQL-396

Fix for DISTMYSQL-243 didn't consider the case when two clusters have
the same suggested custer aliases (the value of it can originate from
ClusterNameToAlias, DetectClusterAliasQuery or be set manually by the
user). In such a case we end up with the situation like:

> create table t1 (a int primary key, b int, unique key (b));
> insert into t1 values (0, 1);
> insert into t1 values (1, 2);
> insert into t1 values (0, 2) on duplicate key update a=0, b=2;
ERROR 1062 (23000): Duplicate entry '2' for key 't1.b'

The fix implements the fallback to REPLACE INTO approach in case of
the failure of the optimized approach using
INSERT INTO ... ON DUPLICATE KEY.

Author: kamil-holubicki

go/inst/cluster_alias_dao.go

@@ -114,65 +114,102 @@ func writeClusterAliasManualOverride(clusterName string, alias string) error {
 	return ExecDBWriteFunc(writeFunc)
 }
 
+// Original, safe approach, which uses REPLACE INTO
+func updateClusterAliasesUsingReplace() error {
+	_, err := db.ExecOrchestrator(`
+	replace into
+			cluster_alias (alias, cluster_name, last_registered)
+		select
+			suggested_cluster_alias,
+				cluster_name,
+				now()
+			from
+			database_instance
+			left join database_instance_downtime using (hostname, port)
+		  where
+			suggested_cluster_alias!=''
+				/* exclude newly demoted, downtimed masters */
+				and ifnull(
+						database_instance_downtime.downtime_active = 1
+						and database_instance_downtime.end_timestamp > now()
+						and database_instance_downtime.reason = ?
+					, 0) = 0
+			order by
+				ifnull(last_checked <= last_seen, 0) asc,
+				read_only desc,
+				num_slave_hosts asc
+	`, DowntimeLostInRecoveryMessage)
+
+	return err
+}
+
+// Optimized approach using INSERT INTO ... ON DUPLICATE KEY UPDATE
+// While this approach is much faster and works in most cases, it is not
+// guaranteed to be working in every case.
+// cluster_alias table has two unique indexes:
+// 1. primary on cluster_name column
+// 2. alias_uidx on alias colum
+//
+// The data which is going to be inserted originates from database_instance
+// table, in particular the following columns:
+// 1. `cluster_name` varchar(128) NOT NULL
+// 2. `suggested_cluster_alias` varchar(128) CHARACTER SET ascii COLLATE
+//	   ascii_general_ci NOT NULL
+//
+// So it is possible to end up in the following situation when we use this
+// approach:
+// create table t1 (a int primary key, b int, unique key (b));
+// insert into t1 values (0, 1);
+// insert into t1 values (1, 2);
+// insert into t1 values (0, 2) on duplicate key update a=0, b=2;
+// ERROR 1062 (23000): Duplicate entry '2' for key 't1.b'
+func updateClusterAliasesUsingInsert() error {
+	_, err := db.ExecOrchestrator(`
+	INSERT INTO cluster_alias
+	(
+		alias,
+		cluster_name,
+		last_registered
+	)
+	SELECT    di.suggested_cluster_alias,
+		  di.cluster_name,
+		  now()
+	FROM      database_instance di
+	LEFT JOIN database_instance_downtime did
+	USING     (hostname, port)
+	WHERE     di.suggested_cluster_alias != ''
+	/* exclude newly demoted, downtimed masters */
+	AND       Ifnull(did.downtime_active = 1
+		  AND did.end_timestamp > Now()
+		  AND did.reason = ?, 0) = 0
+	ORDER BY  Ifnull(di.last_checked <= di.last_seen, 0) ASC,
+		  di.read_only DESC,
+		  di.num_slave_hosts ASC
+	ON DUPLICATE KEY
+	UPDATE alias = di.suggested_cluster_alias,
+	cluster_name = di.cluster_name,
+	last_registered = now()
+	`, DowntimeLostInRecoveryMessage)
+
+	return err
+}
+
 // UpdateClusterAliases writes down the cluster_alias table based on information
 // gained from database_instance
 func UpdateClusterAliases() error {
 	writeFunc := func() error {
 		var err error
 		if IsSQLite() {
 			// Sql lite backend
-			_, err = db.ExecOrchestrator(`
-				replace into
-						cluster_alias (alias, cluster_name, last_registered)
-					select
-					    suggested_cluster_alias,
-							cluster_name,
-							now()
-						from
-					    database_instance
-					    left join database_instance_downtime using (hostname, port)
-					  where
-					    suggested_cluster_alias!=''
-							/* exclude newly demoted, downtimed masters */
-							and ifnull(
-									database_instance_downtime.downtime_active = 1
-									and database_instance_downtime.end_timestamp > now()
-									and database_instance_downtime.reason = ?
-								, 0) = 0
-						order by
-							ifnull(last_checked <= last_seen, 0) asc,
-							read_only desc,
-							num_slave_hosts asc
-				`, DowntimeLostInRecoveryMessage)
+			err = updateClusterAliasesUsingReplace()
 		} else {
 			// MySQL backend (Orchestrator supports only SQLite and MySQL backends)
 			// INSERT ON DUPLICATE KEY UPDATE is more performant than REPLACE in MySQL
-			_, err = db.ExecOrchestrator(`
-				INSERT INTO cluster_alias
-				(
-					alias,
-					cluster_name,
-					last_registered
-				)
-				SELECT    di.suggested_cluster_alias,
-					  di.cluster_name,
-					  now()
-				FROM      database_instance di
-				LEFT JOIN database_instance_downtime did
-				USING     (hostname, port)
-				WHERE     di.suggested_cluster_alias != ''
-				/* exclude newly demoted, downtimed masters */
-				AND       Ifnull(did.downtime_active = 1
-				AND       did.end_timestamp > Now()
-				AND       did.reason = ?, 0) = 0
-				ORDER BY  Ifnull(di.last_checked <= di.last_seen, 0) ASC,
-					  di.read_only DESC,
-					  di.num_slave_hosts ASC
-				ON DUPLICATE KEY
-				UPDATE alias = di.suggested_cluster_alias,
-				cluster_name = di.cluster_name,
-				last_registered = now()
-				`, DowntimeLostInRecoveryMessage)
+			err = updateClusterAliasesUsingInsert()
+			if (err != nil) {
+				// Fallback to the original, safe implementation
+				err = updateClusterAliasesUsingReplace()
+			}
 		}
 		return log.Errore(err)
 	}

script/ensure-go-installed

@@ -1,7 +1,7 @@
 #!/bin/bash
 
 PREFERRED_GO_VERSION=go1.20.3
-SUPPORTED_GO_VERSIONS='go1.1[6789]|go1.2[0]'
+SUPPORTED_GO_VERSIONS='go1.1[6789]|go1.2[01]'
 
 export ROOTDIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )/.." && pwd )"
 cd $ROOTDIR