etcdserver: warn heavy apply

etcdserver/apply.go

@@ -18,6 +18,7 @@ import (
 	"bytes"
 	"fmt"
 	"sort"
+	"time"
 
 	"github.com/coreos/etcd/auth"
 	pb "github.com/coreos/etcd/etcdserver/etcdserverpb"
@@ -33,6 +34,8 @@ const (
 	// To apply with independent Range, Put, Delete, you can pass noTxn
 	// to apply functions instead of a valid txn ID.
 	noTxn = -1
+
+	warnApplyDuration = 10 * time.Millisecond
 )
 
 type applyResult struct {

etcdserver/server.go

@@ -594,7 +594,14 @@ func (s *EtcdServer) run() {
 
 func (s *EtcdServer) applyAll(ep *etcdProgress, apply *apply) {
 	s.applySnapshot(ep, apply)
+	st := time.Now()
 	s.applyEntries(ep, apply)
+	d := time.Since(st)
+	entriesNum := len(apply.entries)
+	if entriesNum != 0 && d > time.Duration(entriesNum)*warnApplyDuration {
+		plog.Warningf("apply entries took too long [%v for %d entries]", d, len(apply.entries))
+		plog.Warningf("avoid queries with large range/delete range!")
+	}
 	// wait for the raft routine to finish the disk writes before triggering a
 	// snapshot. or applied index might be greater than the last index in raft
 	// storage, since the raft routine might be slower than apply routine.