dscache: Only log unusual memcache errors.

filter/dscache/support.go

 // 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 (
         "fmt"
         "math/rand"
         "time"
 
         ds "github.com/luci/gae/service/datastore"
         "github.com/luci/gae/service/memcache"
+        "github.com/luci/luci-go/common/errors"
         log "github.com/luci/luci-go/common/logging"
         "golang.org/x/net/context"
 )
 
 type supportContext struct {
         aid string
         ns  string
 
         c            context.Context
         mc           memcache.Interface
@@ skipping 86 matching lines @@
         }
         if err := s.mc.SetMulti(lockItems); err != nil {
                 // this is a hard failure. No mutation can occur if we're unable to set
                 // locks out. See "DANGER ZONE" in the docs.
                 (log.Fields{log.ErrorKey: err}).Errorf(
                         s.c, "dscache: HARD FAILURE: supportContext.mutation(): mc.SetMulti")
                 return err
         }
         err := f()
         if err == nil {
-                if err := s.mc.DeleteMulti(lockKeys); err != nil {
+                if err := errors.Filter(s.mc.DeleteMulti(lockKeys), memcache.ErrCacheMiss); err != nil {
                         (log.Fields{log.ErrorKey: err}).Warningf(
                                 s.c, "dscache: mc.DeleteMulti")
                 }
         }
         return err
 }
 
 func (s *supportContext) mkRandLockItems(keys []*ds.Key, metas ds.MultiMetaGetter) ([]memcache.Item, []byte) {
         mcKeys := s.mkRandKeys(keys, metas)
         if len(mcKeys) == 0 {
@@ skipping 19 matching lines @@
                 return nil, nil
         }
         ret := make([]memcache.Item, len(mcKeys))
         for i := range ret {
                 ret[i] = (s.mc.NewItem(mcKeys[i]).
                         SetFlags(uint32(ItemHasLock)).
                         SetExpiration(time.Second * time.Duration(LockTimeSeconds)))
         }
         return ret, mcKeys
 }