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>

pkg/services/sqlstore/migrator/postgres_dialect.go

@@ -3,9 +3,11 @@ package migrator
 import (
 	"errors"
 	"fmt"
+	"regexp"
 	"strconv"
 	"strings"
 
+	"github.com/golang-migrate/migrate/v4/database"
 	"github.com/lib/pq"
 
 	"github.com/grafana/grafana/pkg/util/errutil"
@@ -257,3 +259,76 @@ func (db *PostgresDialect) UpsertSQL(tableName string, keyCols, updateCols []str
 	)
 	return s
 }
+
+func (db *PostgresDialect) Lock(cfg LockCfg) error {
+	// trying to obtain the lock for a resource identified by a 64-bit or 32-bit key value
+	// the lock is exclusive: multiple lock requests stack, so that if the same resource is locked three times
+	// it must then be unlocked three times to be released for other sessions' use.
+	// it will either obtain the lock immediately and return true,
+	// or return false if the lock cannot be acquired immediately.
+	query := "SELECT pg_try_advisory_lock(?)"
+	var success bool
+
+	key, err := db.getLockKey()
+	if err != nil {
+		return fmt.Errorf("failed to generate advisory lock key: %w", err)
+	}
+	_, err = cfg.Session.SQL(query, key).Get(&success)
+	if err != nil {
+		return err
+	}
+	if !success {
+		return ErrLockDB
+	}
+
+	return nil
+}
+
+func (db *PostgresDialect) Unlock(cfg LockCfg) error {
+	// trying to release a previously-acquired exclusive session level advisory lock.
+	// it will either return true if the lock is successfully released or
+	// false if the lock was not held (in addition an SQL warning will be reported by the server)
+	query := "SELECT pg_advisory_unlock(?)"
+	var success bool
+
+	key, err := db.getLockKey()
+	if err != nil {
+		return fmt.Errorf("failed to generate advisory lock key: %w", err)
+	}
+	_, err = cfg.Session.SQL(query, key).Get(&success)
+	if err != nil {
+		return err
+	}
+	if !success {
+		return ErrReleaseLockDB
+	}
+	return nil
+}
+
+func getDBName(dsn string) (string, error) {
+	if strings.HasPrefix(dsn, "postgres://") || strings.HasPrefix(dsn, "postgresql://") {
+		parsedDSN, err := pq.ParseURL(dsn)
+		if err != nil {
+			return "", err
+		}
+		dsn = parsedDSN
+	}
+	re := regexp.MustCompile(`dbname=(\w+)`)
+	submatch := re.FindSubmatch([]byte(dsn))
+	if len(submatch) < 2 {
+		return "", fmt.Errorf("failed to get database name")
+	}
+	return string(submatch[1]), nil
+}
+
+func (db *PostgresDialect) getLockKey() (string, error) {
+	dbName, err := getDBName(db.engine.DataSourceName())
+	if err != nil {
+		return "", err
+	}
+	key, err := database.GenerateAdvisoryLockId(dbName)
+	if err != nil {
+		return "", err
+	}
+	return key, nil
+}