Fix concurrency issue when granting privileges on databases (#224)

Co-authored-by: Timothe Genzmer <[email protected]>

Author: timothegenzmer

README.md

@@ -20,7 +20,7 @@ Building The Provider
 Clone repository to: `$GOPATH/src/github.com/cyrilgdn/terraform-provider-postgresql`
 
 ```sh
-$ mkdir -p $GOPATH/src/github.com/terraform-providers; cd $GOPATH/src/github.com/terraform-providers
+$ mkdir -p $GOPATH/src/github.com/cyrilgdn; cd $GOPATH/src/github.com/cyrilgdn
 $ git clone [email protected]:cyrilgdn/terraform-provider-postgresql
 ```
 

postgresql/helpers.go

@@ -477,6 +477,19 @@ func pgLockRole(txn *sql.Tx, role string) error {
 	return nil
 }
 
+// Lock a database and all his members to avoid concurrent updates on some resources
+func pgLockDatabase(txn *sql.Tx, database string) error {
+	// Disable statement timeout for this connection otherwise the lock could fail
+	if _, err := txn.Exec("SET statement_timeout = 0"); err != nil {
+		return fmt.Errorf("could not disable statement_timeout: %w", err)
+	}
+	if _, err := txn.Exec("SELECT pg_advisory_xact_lock(oid::bigint) FROM pg_database WHERE datname = $1", database); err != nil {
+		return fmt.Errorf("could not get advisory lock for database %s: %w", database, err)
+	}
+
+	return nil
+}
+
 func arrayDifference(a, b []interface{}) (diff []interface{}) {
 	m := make(map[interface{}]bool)
 

postgresql/resource_postgresql_grant.go

@@ -150,6 +150,12 @@ func resourcePostgreSQLGrantCreate(db *DBConnection, d *schema.ResourceData) err
 		return err
 	}
 
+	if objectType == "database" {
+		if err := pgLockDatabase(txn, database); err != nil {
+			return err
+		}
+	}
+
 	owners, err := getRolesToGrant(txn, d)
 	if err != nil {
 		return err
@@ -189,7 +195,8 @@ func resourcePostgreSQLGrantDelete(db *DBConnection, d *schema.ResourceData) err
 		return fmt.Errorf("feature is not supported: %v", err)
 	}
 
-	txn, err := startTransaction(db.client, d.Get("database").(string))
+	database := d.Get("database").(string)
+	txn, err := startTransaction(db.client, database)
 	if err != nil {
 		return err
 	}
@@ -200,6 +207,13 @@ func resourcePostgreSQLGrantDelete(db *DBConnection, d *schema.ResourceData) err
 		return err
 	}
 
+	objectType := d.Get("object_type").(string)
+	if objectType == "database" {
+		if err := pgLockDatabase(txn, database); err != nil {
+			return err
+		}
+	}
+
 	owners, err := getRolesToGrant(txn, d)
 	if err != nil {
 		return err