From 3cdb60b548d58abc7e7876094a495d4015a1b96d Mon Sep 17 00:00:00 2001
From: Phil Pluckthun <phil@kitten.sh>
Date: Fri, 24 Apr 2020 17:19:11 +0100
Subject: [PATCH] Split up optimistic result flush logic to two streams

---
 exchanges/graphcache/src/cacheExchange.ts | 52 ++++++++++++-----------
 1 file changed, 28 insertions(+), 24 deletions(-)

diff --git a/exchanges/graphcache/src/cacheExchange.ts b/exchanges/graphcache/src/cacheExchange.ts
index ab1f27fdfa..f80b5985db 100644
--- a/exchanges/graphcache/src/cacheExchange.ts
+++ b/exchanges/graphcache/src/cacheExchange.ts
@@ -17,7 +17,6 @@ import {
   share,
   fromPromise,
   fromArray,
-  fromValue,
   buffer,
   take,
   mergeMap,
@@ -384,41 +383,46 @@ export const cacheExchange = (opts?: CacheExchangeOpts): Exchange => ({
     const result$ = pipe(
       merge([nonCacheOps$, cacheMissOps$]),
       map(prepareForwardedOperation),
-      forward
+      forward,
+      share
+    );
+
+    // Results that can immediately be resolved
+    const nonOptimisticResults$ = pipe(
+      result$,
+      filter(result => !optimisticKeysToDependencies.has(result.operation.key))
     );
 
     // Prevent mutations that were previously optimistic from being flushed
     // immediately and instead clear them out slowly
-    const resultWithUpdate$ = pipe(
+    const optimisticMutationCompletion$ = pipe(
       result$,
+      filter(result => optimisticKeysToDependencies.has(result.operation.key)),
       mergeMap(
         (result: OperationResult): Source<OperationResult> => {
-          if (optimisticKeysToDependencies.has(result.operation.key)) {
-            mutationResultBuffer.push(result);
-            if (
-              mutationResultBuffer.length < optimisticKeysToDependencies.size
-            ) {
-              return empty;
-            }
-
-            for (let i = 0; i < mutationResultBuffer.length; i++) {
-              clearLayer(store.data, mutationResultBuffer[i].operation.key);
-            }
-
-            const results: OperationResult[] = [];
-            let bufferedResult: OperationResult | void;
-            while ((bufferedResult = mutationResultBuffer.shift()))
-              results.push(updateCacheWithResult(bufferedResult));
+          const length = mutationResultBuffer.push(result);
+          if (length < optimisticKeysToDependencies.size) {
+            return empty;
+          }
 
-            return fromArray(results);
+          for (let i = 0; i < mutationResultBuffer.length; i++) {
+            clearLayer(store.data, mutationResultBuffer[i].operation.key);
           }
 
-          return fromValue(updateCacheWithResult(result));
+          const results: OperationResult[] = [];
+          let bufferedResult: OperationResult | void;
+          while ((bufferedResult = mutationResultBuffer.shift()))
+            results.push(updateCacheWithResult(bufferedResult));
+
+          return fromArray(results);
         }
-      ),
-      filter(result => !!result)
+      )
     );
 
-    return merge([resultWithUpdate$, cacheResult$]);
+    return merge([
+      nonOptimisticResults$,
+      optimisticMutationCompletion$,
+      cacheResult$,
+    ]);
   };
 };