fix: prevent max listeners warning

If establishing a database connection is slow and database migration runs and there are many models, sql operations are queued up and this leads to the node.js max emitters exceeded warning. A default value for max emitters has now been introduced, and it can also be configured in datasources.json. Signed-off-by: Dominique Emond <[email protected]>
loopbackio · Aug 1, 2019 · afdc19b · afdc19b
1 parent ad4edc6
commit afdc19b
Showing 1 changed file with 21 additions and 0 deletions.
diff --git a/lib/datasource.js b/lib/datasource.js
@@ -207,6 +207,11 @@ DataSource.prototype._setupConnector = function() {
       this.connector.dataSource = this;
     }
     const dataSource = this;
+
+    // Set max listeners to a default/configured value
+    // solves bug https://github.com/strongloop/loopback-next/issues/2198
+    dataSource.setMaxListeners(dataSource.getMaxOfflineRequests());
+
     this.connector.log = function(query, start) {
       dataSource.log(query, start);
     };
@@ -2699,6 +2704,22 @@ DataSource.prototype.beginTransaction = function(options) {
   return Transaction.begin(this.connector, options);
 };
 
+/**
+ * Get the maximum number of event listeners
+ */
+DataSource.prototype.getMaxOfflineRequests = function() {
+    // Set max listeners to a default value
+    // Override this default value with a datasource setting
+    // 'maxOfflineRequests' from an application's datasources.json
+    // solves bug https://github.com/strongloop/loopback-next/issues/2198
+    let maxOfflineRequests = 16;
+    if (this.settings && this.settings.maxOfflineRequests) {
+      if (this.settings.maxOfflineRequests > maxOfflineRequests)
+        maxOfflineRequests = this.settings.maxOfflineRequests;
+    }
+  return maxOfflineRequests;
+};
+
 /*! The hidden property call is too expensive so it is not used that much
 */
 /**