tikv: collapse duplicate resolve locks in region requests (#16838)

store/tikv/client_collapse.go

@@ -0,0 +1,92 @@
+// Copyright 2020 PingCAP, Inc.
+//
+// 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,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package tikv provides tcp connection to kvserver.
+package tikv
+
+import (
+	"context"
+	"strconv"
+	"time"
+
+	"github.com/pingcap/errors"
+	"github.com/pingcap/tidb/store/tikv/tikvrpc"
+	"golang.org/x/sync/singleflight"
+)
+
+var _ Client = reqCollapse{}
+
+var resolveRegionSf singleflight.Group
+
+type reqCollapse struct {
+	Client
+}
+
+func (r reqCollapse) Close() error {
+	if r.Client == nil {
+		panic("client should not be nil")
+	}
+	return r.Client.Close()
+}
+
+func (r reqCollapse) SendRequest(ctx context.Context, addr string, req *tikvrpc.Request, timeout time.Duration) (*tikvrpc.Response, error) {
+	if r.Client == nil {
+		panic("client should not be nil")
+	}
+	if canCollapse, resp, err := r.tryCollapseRequest(ctx, addr, req, timeout); canCollapse {
+		return resp, err
+	}
+	return r.Client.SendRequest(ctx, addr, req, timeout)
+}
+
+func (r reqCollapse) tryCollapseRequest(ctx context.Context, addr string, req *tikvrpc.Request, timeout time.Duration) (canCollapse bool, resp *tikvrpc.Response, err error) {
+	switch req.Type {
+	case tikvrpc.CmdResolveLock:
+		resolveLock := req.ResolveLock()
+		if len(resolveLock.Keys) > 0 {
+			// can not collapse resolve lock lite
+			return
+		}
+		canCollapse = true
+		key := strconv.FormatUint(resolveLock.Context.RegionId, 10) + "-" + strconv.FormatUint(resolveLock.StartVersion, 10)
+		resp, err = r.collapse(ctx, key, &resolveRegionSf, addr, req, timeout)
+		return
+	default:
+		// now we only support collapse resolve lock.
+		return
+	}
+}
+
+func (r reqCollapse) collapse(ctx context.Context, key string, sf *singleflight.Group,
+	addr string, req *tikvrpc.Request, timeout time.Duration) (resp *tikvrpc.Response, err error) {
+	rsC := sf.DoChan(key, func() (interface{}, error) {
+		return r.Client.SendRequest(context.Background(), addr, req, readTimeoutShort) // use resolveLock timeout.
+	})
+	timer := time.NewTimer(timeout)
+	defer timer.Stop()
+	select {
+	case <-ctx.Done():
+		err = errors.Trace(ctx.Err())
+		return
+	case <-timer.C:
+		err = errors.Trace(context.DeadlineExceeded)
+		return
+	case rs := <-rsC:
+		if rs.Err != nil {
+			err = errors.Trace(rs.Err)
+			return
+		}
+		resp = rs.Val.(*tikvrpc.Response)
+		return
+	}
+}

store/tikv/kv.go

@@ -201,7 +201,7 @@ func newTikvStore(uuid string, pdClient pd.Client, spkv SafePointKV, client Clie
 		clusterID:       pdClient.GetClusterID(context.TODO()),
 		uuid:            uuid,
 		oracle:          o,
-		client:          client,
+		client:          reqCollapse{client},
 		pdClient:        pdClient,
 		regionCache:     NewRegionCache(pdClient),
 		coprCache:       nil,