Add part of cache back.

Signed-off-by: Antonio Navarro Perez <antnavper@gmail.com>

etcd/cache.go

@@ -0,0 +1,57 @@
+// Copyright 2017 Pilosa Corp.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package etcd
+
+import (
+	"sync"
+	"time"
+
+	"github.com/pilosa/pilosa/v2/topology"
+)
+
+// EtcdWithCache is a wrapper around the Etcd type which will return a
+// cached value when the number of requests come in below a configured
+// frequency. It also breaks the cache after a configured TTL.
+type EtcdWithCache struct {
+	*Etcd
+
+	peersMu sync.Mutex // peer-list cache updates
+
+	nodes            []*topology.Node // unmarshalled Node data
+	nodesTTL         int              // seconds
+	nodesLastRequest time.Time        // last time requested
+}
+
+// NewEtcdWithCache returns a new instance of Cache.
+func NewEtcdWithCache(opt Options, replicas int) *EtcdWithCache {
+	return &EtcdWithCache{
+		Etcd: NewEtcd(opt, replicas),
+
+		nodesTTL: 6,
+	}
+}
+
+// Nodes caches the result of the underlying implementation's node list.
+func (c *EtcdWithCache) Nodes() []*topology.Node {
+	c.peersMu.Lock()
+	defer c.peersMu.Unlock()
+
+	now := time.Now()
+	if now.Sub(c.nodesLastRequest) > (time.Duration(c.nodesTTL) * time.Second) {
+		c.nodes = c.Etcd.Nodes()
+		c.nodesLastRequest = now
+	}
+	return c.nodes
+}

server/server.go

@@ -391,7 +391,7 @@ func (m *Command) SetupServer() error {
 		m.Config.Etcd.Dir = filepath.Join(path, pilosa.DefaultDiscoDir)
 	}
 
-	e := petcd.NewEtcd(m.Config.Etcd, m.Config.Cluster.ReplicaN)
+	e := petcd.NewEtcdWithCache(m.Config.Etcd, m.Config.Cluster.ReplicaN)
 	discoOpt := pilosa.OptServerDisCo(e, e, e, e, e, e, e)
 
 	serverOptions := []pilosa.ServerOption{