Avoid copying entire cache on each optimistic read.

CHANGELOG.md

@@ -43,11 +43,19 @@
 
 ### Apollo Cache In-Memory (vNext)
 
+- The speed and memory usage of optimistic reads and writes has been
+  improved dramatically using a new layering technique that does not
+  require copying the non-optimistic contents of the cache.
+  [PR #4319](https://github.com/apollographql/apollo-client/pull/4319/)
+
+- The `RecordingCache` abstraction has been removed, and thus is no longer
+  exported from `apollo-cache-inmemory`.
+  [PR #4319](https://github.com/apollographql/apollo-client/pull/4319/)
+
 - Export the optimism `wrap` function using ES2015 export syntax, instead of
   CommonJS.  <br/>
   [@ardatan](https://github.com/ardatan) in [#4158](https://github.com/apollographql/apollo-client/pull/4158)
 
-
 ## Apollo Client (2.4.8)
 
 ### Apollo Client (2.4.8)

packages/apollo-cache-inmemory/src/__tests__/recordingCache.ts

@@ -1,43 +1,47 @@
-import { RecordingCache } from '../recordingCache';
+import { OptimisticCacheLayer } from '../inMemoryCache';
+import { ObjectCache } from '../objectCache';
 import { NormalizedCacheObject } from '../types';
 
-describe('RecordingCache', () => {
+describe('OptimisticCacheLayer', () => {
+  function makeLayer(root: ObjectCache) {
+    return new OptimisticCacheLayer('whatever', root, () => {});
+  }
+
   describe('returns correct values during recording', () => {
     const data = {
       Human: { __typename: 'Human', name: 'Mark' },
       Animal: { __typename: 'Mouse', name: '🐭' },
     };
-    const dataToRecord = { Human: { __typename: 'Human', name: 'John' } };
-    let cache: RecordingCache;
 
+    const dataToRecord = {
+      Human: { __typename: 'Human', name: 'John' },
+    };
+
+    const underlyingCache = new ObjectCache(data);
+
+    let cache = makeLayer(underlyingCache);
     beforeEach(() => {
-      cache = new RecordingCache({ ...data });
+      cache = makeLayer(underlyingCache);
     });
 
     it('should passthrough values if not defined in recording', () => {
-      cache.record(() => {
-        expect(cache.get('Human')).toBe(data.Human);
-        expect(cache.get('Animal')).toBe(data.Animal);
-      });
+      expect(cache.get('Human')).toBe(data.Human);
+      expect(cache.get('Animal')).toBe(data.Animal);
     });
 
     it('should return values defined during recording', () => {
-      const recording = cache.record(() => {
-        cache.set('Human', dataToRecord.Human);
-        expect(cache.get('Human')).toBe(dataToRecord.Human);
-      });
-      expect(recording.Human).toBe(dataToRecord.Human);
+      cache.set('Human', dataToRecord.Human);
+      expect(cache.get('Human')).toBe(dataToRecord.Human);
+      expect(underlyingCache.get('Human')).toBe(data.Human);
     });
 
     it('should return undefined for values deleted during recording', () => {
-      const recording = cache.record(() => {
-        expect(cache.get('Animal')).toBe(data.Animal);
-        // delete should be registered in the recording:
-        cache.delete('Animal');
-        expect(cache.get('Animal')).toBeUndefined();
-      });
-
-      expect(recording).toHaveProperty('Animal');
+      expect(cache.get('Animal')).toBe(data.Animal);
+      // delete should be registered in the recording:
+      cache.delete('Animal');
+      expect(cache.get('Animal')).toBeUndefined();
+      expect(cache.toObject()).toHaveProperty('Animal');
+      expect(underlyingCache.get('Animal')).toBe(data.Animal);
     });
   });
 
@@ -46,16 +50,20 @@ describe('RecordingCache', () => {
       Human: { __typename: 'Human', name: 'Mark' },
       Animal: { __typename: 'Mouse', name: '🐭' },
     };
-    const dataToRecord = { Human: { __typename: 'Human', name: 'John' } };
-    let cache: RecordingCache;
+
+    const dataToRecord = {
+      Human: { __typename: 'Human', name: 'John' },
+    };
+
+    const underlyingCache = new ObjectCache(data);
+    let cache = makeLayer(underlyingCache);
     let recording: NormalizedCacheObject;
 
     beforeEach(() => {
-      cache = new RecordingCache({ ...data });
-      recording = cache.record(() => {
-        cache.set('Human', dataToRecord.Human);
-        cache.delete('Animal');
-      });
+      cache = makeLayer(underlyingCache);
+      cache.set('Human', dataToRecord.Human);
+      cache.delete('Animal');
+      recording = cache.toObject();
     });
 
     it('should contain the property indicating deletion', () => {
@@ -70,7 +78,7 @@ describe('RecordingCache', () => {
     });
 
     it('should keep the original data unaffected', () => {
-      expect(cache.toObject()).toEqual(data);
+      expect(underlyingCache.toObject()).toEqual(data);
     });
   });
 });