[8.4.x]: SQLStore: Prevent concurrent migrations (#44101) (#45447)

* SQLStore: Prevent concurrent migrations (#44101)

* SQLStore: Prevent concurrent migrations

* Hide behind a feature toggle

* Configurable locking attempt timeout

* Update docs/sources/administration/configuration.md

Co-authored-by: Igor Suleymanov <radiohead@users.noreply.github.com>
Co-authored-by: achatterjee-grafana <70489351+achatterjee-grafana@users.noreply.github.com>
(cherry picked from commit d718ee1918)

* Resolve dependency cycle (#45427)

(cherry picked from commit 6a38ce2307)

pkg/services/sqlstore/migrator/mysql_dialect.go

@@ -1,6 +1,7 @@
 package migrator
 
 import (
+	"database/sql"
 	"errors"
 	"fmt"
 	"strconv"
@@ -8,6 +9,7 @@ import (
 
 	"github.com/VividCortex/mysqlerr"
 	"github.com/go-sql-driver/mysql"
+	"github.com/golang-migrate/migrate/v4/database"
 	"github.com/grafana/grafana/pkg/util/errutil"
 	"xorm.io/xorm"
 )
@@ -225,3 +227,66 @@ func (db *MySQLDialect) UpsertSQL(tableName string, keyCols, updateCols []string
 	)
 	return s
 }
+
+func (db *MySQLDialect) Lock(cfg LockCfg) error {
+	query := "SELECT GET_LOCK(?, ?)"
+	var success sql.NullBool
+
+	lockName, err := db.getLockName()
+	if err != nil {
+		return fmt.Errorf("failed to generate lock name: %w", err)
+	}
+
+	// trying to obtain the lock with the specific name
+	// the lock is exclusive per session and is released explicitly by executing RELEASE_LOCK() or implicitly when the session terminates
+	// it returns 1 if the lock was obtained successfully,
+	// 0 if the attempt timed out (for example, because another client has previously locked the name),
+	// or NULL if an error occurred
+	// starting from MySQL 5.7 it is even possible for a given session to acquire multiple locks for the same name
+	// however other sessions cannot acquire a lock with that name until the acquiring session releases all its locks for the name.
+	_, err = cfg.Session.SQL(query, lockName, cfg.Timeout).Get(&success)
+	if err != nil {
+		return err
+	}
+	if !success.Valid || !success.Bool {
+		return ErrLockDB
+	}
+	return nil
+}
+
+func (db *MySQLDialect) Unlock(cfg LockCfg) error {
+	query := "SELECT RELEASE_LOCK(?)"
+	var success sql.NullBool
+
+	lockName, err := db.getLockName()
+	if err != nil {
+		return fmt.Errorf("failed to generate lock name: %w", err)
+	}
+
+	// trying to release the lock with the specific name
+	// it returns 1 if the lock was released,
+	// 0 if the lock was not established by this thread (in which case the lock is not released),
+	// and NULL if the named lock did not exist (it was never obtained by a call to GET_LOCK() or if it has previously been released)
+	_, err = cfg.Session.SQL(query, lockName).Get(&success)
+	if err != nil {
+		return err
+	}
+	if !success.Valid || !success.Bool {
+		return ErrReleaseLockDB
+	}
+	return nil
+}
+
+func (db *MySQLDialect) getLockName() (string, error) {
+	cfg, err := mysql.ParseDSN(db.engine.DataSourceName())
+	if err != nil {
+		return "", err
+	}
+
+	s, err := database.GenerateAdvisoryLockId(cfg.DBName)
+	if err != nil {
+		return "", fmt.Errorf("failed to generate advisory lock key: %w", err)
+	}
+
+	return s, nil
+}