A transparent cache for datastore, backed by memcache.

filter/dscache/context.go

Index: filter/dscache/context.go
diff --git a/filter/dscache/context.go b/filter/dscache/context.go
new file mode 100644
index 0000000000000000000000000000000000000000..1f7df9d93b99c8e10e5c6a3a83f415b5a366eac0
--- /dev/null
+++ b/filter/dscache/context.go
@@ -0,0 +1,32 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package dscache
+
+import (
+	ds "github.com/luci/gae/service/datastore"
+	"github.com/luci/gae/service/info"
+	mc "github.com/luci/gae/service/memcache"
+	"github.com/luci/luci-go/common/logging"
+	"github.com/luci/luci-go/common/mathrand"
+	"golang.org/x/net/context"
+)
+
+type key int
+
+var dsTxnCacheKey key
+
+// FilterRDS installs a counter RawDatastore filter in the context.
+func FilterRDS(c context.Context) context.Context {
+	return ds.AddRawFilters(c, func(ic context.Context, ds ds.RawInterface) ds.RawInterface {
+		i := info.Get(ic)
+		aid, ns := i.AppID(), i.GetNamespace()
+
+		v := ic.Value(dsTxnCacheKey)
+		if v == nil {
+			return &dsCache{ds, aid, ns, mc.Get(ic), logging.Get(ic), mathrand.Get(ic)}
+		}
+		return &dsTxnCache{ds, v.(*dsTxnState), mc.Get(ic)}
+	})
+}