Merge pull request #320 from FlowFuse/319-flush-batching

Batch requests to flush context to backend

Author: hardillb

lib/context/FFContextStorage.js

@@ -111,24 +111,30 @@ class FFContextStorage {
             }
         }
         // update _flushPendingWrites to a real function
-        self._flushPendingWrites = function () {
+        self._flushPendingWrites = async function () {
             const scopes = Object.keys(self.pendingWrites)
             self.pendingWrites = {}
-            const promises = []
             const newContext = self.cache._export()
-            scopes.forEach(function (scope) {
-                const context = newContext[scope] || {}
-                const stringifiedContext = stringify(context)
-                if (stringifiedContext.circular && !self.knownCircularRefs[scope]) {
-                    console.warn('context.flowforge.error-circular', scope)
-                    self.knownCircularRefs[scope] = true
-                } else {
-                    delete self.knownCircularRefs[scope]
-                }
-                promises.push(self._writeCache(scope, stringifiedContext.json))
-            })
+            // Batch requests into a maximum of 5 at a time to avoid contention
+            // on the file-server
+            const chunkSize = 5
+            while (scopes.length > 0) {
+                // Grab a chunk of the pending scopes
+                const batch = scopes.splice(0, chunkSize)
+                // For each one, trigger the flush call and await all in the batch to complete
+                await Promise.all(batch.map((scope) => {
+                    const context = newContext[scope] || {}
+                    const stringifiedContext = stringify(context)
+                    if (stringifiedContext.circular && !self.knownCircularRefs[scope]) {
+                        console.warn('context.flowforge.error-circular', scope)
+                        self.knownCircularRefs[scope] = true
+                    } else {
+                        delete self.knownCircularRefs[scope]
+                    }
+                    return self._writeCache(scope, stringifiedContext.json)
+                }))
+            }
             delete self._pendingWriteTimeout
-            return Promise.all(promises)
         }
     }