optimize the performance of lightning (#281)

* lightning: split large csv file if possible

* gofmt

* gofmt

* unit test

* add unit test

* tiny change

* tiny refine

* fix ci

* remove useless code

* fix ci

* fix ci

* address comments

* go fmt for all

* Replace CSV Ragel parser by a hand-written parser copied from encoding/csv

Conflicts:
	lightning/mydump/csv_parser_generated.go

* fix conflict

* update

* update again

* send a batch of kv in encodeLoop

* use sync.Pool

* Close channel instead of push one entry.

* Use copy instead append

* Fix test and failpoint version

* Reuse slice of record

This expected to avoid about 3.5% of alloc_objects
alloc_objects:
  Total:   773496750  773873722 (flat, cum)  7.18%
    177            .          .           	parser.fieldIndexes = parser.fieldIndexes[:0]
    178            .          .
    179            .          .           	isEmptyLine := true
...
    225    386621314  386621314           	str := string(parser.recordBuffer) // Convert to string once to batch allocations
    226    386875436  386875436           	dst := make([]string, len(parser.fieldIndexes))

* Use pool for mutation

This take most alloc in WriteRows:
    ROUTINE ======================== github.com/pingcap/tidb-lightning/lightning/backend.(*importer).WriteRows in /Users/huangjiahao/go/src/github.com/pingcap/tidb-lightning/lightning/backend/importer.go
     797370418  980241246 (flat, cum)  9.09% of Total
             .          .    155:   kvs := rows.(kvPairs)
    ...
    ...
             .          .    192:   for i, pair := range kvs {
     772641868  772641868    193:           mutations[i] = &kv.Mutation{
             .          .    194:                   Op:    kv.Mutation_Put,
             .          .    195:                   Key:   pair.Key,
             .          .    196:                   Value: pair.Val,
             .          .    197:           }
             .          .    198:   }

* Set GC percent as 500 default

Lightning allocates too many transient objects and heap size is small,
so garbage collections happen too frequently and lots of time is spent in GC component.

In a test of loading the table `order_line.csv` of 14k TPCC.
The time need of `encode kv data and write` step reduce from 52m4s to 37m30s when change
GOGC from 100 to 500, the total time needed reduce near 15m too.
The cost of this is the memory of lightnin at runtime grow from about 200M to 700M, but it's acceptable.

So we set the gc percentage as 500 default to reduce the GC frequency instead of 100.

* Remove MaxKVPairs in Mydump

has been move to Importer part

* Remove outdate code

* Update tidb version

For pingcap/tidb@495f8b7
disable UpdateDeltaForTable if TxnCtx is nil

* Address comment

* Remain append

Co-authored-by: xuhuaiyu <391585975@qq.com>

cmd/tidb-lightning/main.go

@@ -17,6 +17,7 @@ import (
 	"fmt"
 	"os"
 	"os/signal"
+	"runtime/debug"
 	"syscall"
 
 	"github.com/pingcap/tidb-lightning/lightning"
@@ -44,6 +45,21 @@ func main() {
 
 	logger := log.L()
 
+	// Lightning allocates too many transient objects and heap size is small,
+	// so garbage collections happen too frequently and lots of time is spent in GC component.
+	//
+	// In a test of loading the table `order_line.csv` of 14k TPCC.
+	// The time need of `encode kv data and write` step reduce from 52m4s to 37m30s when change
+	// GOGC from 100 to 500, the total time needed reduce near 15m too.
+	// The cost of this is the memory of lightnin at runtime grow from about 200M to 700M, but it's acceptable.
+	//
+	// So we set the gc percentage as 500 default to reduce the GC frequency instead of 100.
+	gogc := os.Getenv("GOGC")
+	if gogc == "" {
+		old := debug.SetGCPercent(500)
+		log.L().Debug("set gc percentage", zap.Int("old", old), zap.Int("new", 500))
+	}
+
 	err := app.GoServe()
 	if err != nil {
 		logger.Error("failed to start HTTP server", zap.Error(err))

go.mod

@@ -10,13 +10,13 @@ require (
 	github.com/gogo/protobuf v1.3.1
 	github.com/golang/mock v1.4.0
 	github.com/joho/sqltocsv v0.0.0-20190824231449-5650f27fd5b6
-	github.com/pingcap/check v0.0.0-20191216031241-8a5a85928f12
+	github.com/pingcap/check v0.0.0-20200212061837-5e12011dc712
 	github.com/pingcap/errors v0.11.5-0.20190809092503-95897b64e011
-	github.com/pingcap/failpoint v0.0.0-20191029060244-12f4ac2fd11d
-	github.com/pingcap/kvproto v0.0.0-20200108025604-a4dc183d2af5
-	github.com/pingcap/log v0.0.0-20191012051959-b742a5d432e9
-	github.com/pingcap/parser v0.0.0-20200109073933-a9496438d77d
-	github.com/pingcap/tidb v1.1.0-beta.0.20200110130413-8c3ee37c1938
+	github.com/pingcap/failpoint v0.0.0-20200210140405-f8f9fb234798
+	github.com/pingcap/kvproto v0.0.0-20200221125103-35b65c96516e
+	github.com/pingcap/log v0.0.0-20200117041106-d28c14d3b1cd
+	github.com/pingcap/parser v0.0.0-20200218113622-517beb2e39c2
+	github.com/pingcap/tidb v1.1.0-beta.0.20200303031609-495f8b74382f
 	github.com/pingcap/tidb-tools v4.0.0-beta+incompatible
 	github.com/prometheus/client_golang v1.4.0
 	github.com/prometheus/client_model v0.2.0

lightning/backend/importer.go

@@ -16,6 +16,7 @@ package backend
 import (
 	"context"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/pingcap/errors"
@@ -39,6 +40,8 @@ type importer struct {
 	conn   *grpc.ClientConn
 	cli    kv.ImportKVClient
 	pdAddr string
+
+	mutationPool sync.Pool
 }
 
 // NewImporter creates a new connection to tikv-importer. A single connection
@@ -50,9 +53,10 @@ func NewImporter(ctx context.Context, tls *common.TLS, importServerAddr string,
 	}
 
 	return MakeBackend(&importer{
-		conn:   conn,
-		cli:    kv.NewImportKVClient(conn),
-		pdAddr: pdAddr,
+		conn:         conn,
+		cli:          kv.NewImportKVClient(conn),
+		pdAddr:       pdAddr,
+		mutationPool: sync.Pool{New: func() interface{} { return &kv.Mutation{} }},
 	}), nil
 }
 
@@ -61,9 +65,10 @@ func NewImporter(ctx context.Context, tls *common.TLS, importServerAddr string,
 // outside of tests.
 func NewMockImporter(cli kv.ImportKVClient, pdAddr string) Backend {
 	return MakeBackend(&importer{
-		conn:   nil,
-		cli:    cli,
-		pdAddr: pdAddr,
+		conn:         nil,
+		cli:          cli,
+		pdAddr:       pdAddr,
+		mutationPool: sync.Pool{New: func() interface{} { return &kv.Mutation{} }},
 	})
 }
 
@@ -190,11 +195,10 @@ func (importer *importer) WriteRows(
 	// Send kv paris as write request content
 	mutations := make([]*kv.Mutation, len(kvs))
 	for i, pair := range kvs {
-		mutations[i] = &kv.Mutation{
-			Op:    kv.Mutation_Put,
-			Key:   pair.Key,
-			Value: pair.Val,
-		}
+		mutations[i] = importer.mutationPool.Get().(*kv.Mutation)
+		mutations[i].Op = kv.Mutation_Put
+		mutations[i].Key = pair.Key
+		mutations[i].Value = pair.Val
 	}
 
 	req.Reset()
@@ -205,7 +209,12 @@ func (importer *importer) WriteRows(
 		},
 	}
 
-	if err := wstream.Send(req); err != nil {
+	err = wstream.Send(req)
+	for _, mutation := range mutations {
+		importer.mutationPool.Put(mutation)
+	}
+
+	if err != nil {
 		return errors.Trace(err)
 	}
 

lightning/backend/importer_test.go

@@ -2,13 +2,16 @@ package backend_test
 
 import (
 	"context"
+	"sync"
+	"testing"
 
 	"github.com/golang/mock/gomock"
 	. "github.com/pingcap/check"
 	"github.com/pingcap/errors"
 	"github.com/pingcap/kvproto/pkg/import_kvpb"
 	uuid "github.com/satori/go.uuid"
 
+	kvpb "github.com/pingcap/kvproto/pkg/import_kvpb"
 	kv "github.com/pingcap/tidb-lightning/lightning/backend"
 	"github.com/pingcap/tidb-lightning/lightning/common"
 	"github.com/pingcap/tidb-lightning/mock"
@@ -193,3 +196,39 @@ func (s *importerSuite) TestCloseImportCleanupEngine(c *C) {
 	err = engine.Cleanup(s.ctx)
 	c.Assert(err, IsNil)
 }
+
+func BenchmarkMutationAlloc(b *testing.B) {
+	var g *kvpb.Mutation
+	for i := 0; i < b.N; i++ {
+		m := &kvpb.Mutation{
+			Op:    kvpb.Mutation_Put,
+			Key:   nil,
+			Value: nil,
+		}
+		g = m
+	}
+
+	var _ = g
+}
+
+func BenchmarkMutationPool(b *testing.B) {
+	p := sync.Pool{
+		New: func() interface{} {
+			return &kvpb.Mutation{}
+		},
+	}
+	var g *kvpb.Mutation
+
+	for i := 0; i < b.N; i++ {
+		m := p.Get().(*kvpb.Mutation)
+		m.Op = kvpb.Mutation_Put
+		m.Key = nil
+		m.Value = nil
+
+		g = m
+
+		p.Put(m)
+	}
+
+	var _ = g
+}

lightning/backend/session.go

@@ -106,17 +106,14 @@ func newSession(options *SessionOptions) *session {
 	vars.StmtCtx.TimeZone = vars.Location()
 	vars.SetSystemVar("timestamp", strconv.FormatInt(options.Timestamp, 10))
 	vars.SetSystemVar(variable.TiDBRowFormatVersion, options.RowFormatVersion)
+	vars.TxnCtx = nil
 
 	s := &session{
 		txn:  transaction{},
 		vars: vars,
 	}
 	s.vars.GetWriteStmtBufs().BufStore = &kv.BufferStore{MemBuffer: &s.txn}
 
-	// FIXME: potential further improvements:
-	//  - (*TransactionContext).UpdateDeltaForTable takes 14% of Encode() time.
-	//    But we cannot make `vars.TxnCtx` into nil nor make it no-op.
-
 	return s
 }
 

lightning/mydump/csv_parser.go

@@ -50,6 +50,8 @@ type CSVParser struct {
 	// fieldIndexes is an index of fields inside recordBuffer.
 	// The i'th field ends at offset fieldIndexes[i] in recordBuffer.
 	fieldIndexes []int
+
+	lastRecord []string
 }
 
 func NewCSVParser(
@@ -163,7 +165,7 @@ func (parser *CSVParser) readUntil(chars string) ([]byte, byte, error) {
 	}
 }
 
-func (parser *CSVParser) readRecord() ([]string, error) {
+func (parser *CSVParser) readRecord(dst []string) ([]string, error) {
 	parser.recordBuffer = parser.recordBuffer[:0]
 	parser.fieldIndexes = parser.fieldIndexes[:0]
 
@@ -214,7 +216,11 @@ outside:
 	// Create a single string and create slices out of it.
 	// This pins the memory of the fields together, but allocates once.
 	str := string(parser.recordBuffer) // Convert to string once to batch allocations
-	dst := make([]string, len(parser.fieldIndexes))
+	dst = dst[:0]
+	if cap(dst) < len(parser.fieldIndexes) {
+		dst = make([]string, len(parser.fieldIndexes))
+	}
+	dst = dst[:len(parser.fieldIndexes)]
 	var preIdx int
 	for i, idx := range parser.fieldIndexes {
 		dst[i] = str[preIdx:idx]
@@ -315,7 +321,7 @@ func (parser *CSVParser) ReadRow() error {
 
 	// skip the header first
 	if parser.pos == 0 && parser.cfg.Header {
-		columns, err := parser.readRecord()
+		columns, err := parser.readRecord(nil)
 		if err != nil {
 			return errors.Trace(err)
 		}
@@ -326,10 +332,11 @@ func (parser *CSVParser) ReadRow() error {
 		}
 	}
 
-	records, err := parser.readRecord()
+	records, err := parser.readRecord(parser.lastRecord)
 	if err != nil {
 		return errors.Trace(err)
 	}
+	parser.lastRecord = records
 	// remove trailing empty values
 	if parser.cfg.TrimLastSep {
 		var i int
@@ -345,7 +352,7 @@ func (parser *CSVParser) ReadRow() error {
 		if isNull {
 			datum.SetNull()
 		} else {
-			datum.SetString(unescaped)
+			datum.SetString(unescaped, "utf8mb4_bin")
 		}
 		row.Row = append(row.Row, datum)
 	}

lightning/mydump/parser.go

@@ -472,7 +472,7 @@ func (parser *ChunkParser) ReadRow() error {
 				// can't handle integers more than 64 bits anyway)
 				fallthrough
 			case tokUnquoted, tokSingleQuoted, tokDoubleQuoted:
-				value.SetString(parser.unescapeString(string(content)))
+				value.SetString(parser.unescapeString(string(content)), "utf8mb4_bin")
 			case tokHexString:
 				hexLit, err := types.ParseHexStr(string(content))
 				if err != nil {

lightning/restore/restore.go

@@ -581,7 +581,7 @@ func (rc *RestoreController) restoreTables(ctx context.Context) error {
 
 	var restoreErr common.OnceError
 
-	stopPeriodicActions := make(chan struct{}, 1)
+	stopPeriodicActions := make(chan struct{})
 	go rc.runPeriodicActions(ctx, stopPeriodicActions)
 
 	type task struct {
@@ -691,7 +691,7 @@ func (rc *RestoreController) restoreTables(ctx context.Context) error {
 	}
 
 	wg.Wait()
-	stopPeriodicActions <- struct{}{}
+	close(stopPeriodicActions)
 
 	err := restoreErr.Get()
 	logTask.End(zap.ErrorLevel, err)
@@ -948,7 +948,7 @@ func (t *TableRestore) restoreEngine(
 	totalSQLSize := int64(0)
 	for _, chunk := range cp.Chunks {
 		totalKVSize += chunk.Checksum.SumSize()
-		totalSQLSize += chunk.Chunk.EndOffset
+		totalSQLSize += chunk.Chunk.EndOffset - chunk.Chunk.Offset
 	}
 
 	err = chunkErr.Get()

tools/go.mod

@@ -5,6 +5,6 @@ go 1.12
 require (
 	github.com/golangci/golangci-lint v1.22.2
 	github.com/mgechev/revive v1.0.0
-	github.com/pingcap/failpoint v0.0.0-20191029060244-12f4ac2fd11d
+	github.com/pingcap/failpoint v0.0.0-20200210140405-f8f9fb234798
 	github.com/shurcooL/vfsgen v0.0.0-20181202132449-6a9ea43bcacd
 )

tools/go.sum

@@ -1,4 +1,5 @@
 cloud.google.com/go v0.26.0/go.mod h1:aQUYkXzVsufM+DwF1aE+0xfcU+56JwCaLick0ClmMTw=
+github.com/BurntSushi/toml v0.3.1 h1:WXkYYl6Yr3qBf1K79EBnL4mak0OimBfB0XUf9Vl28OQ=
 github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
 github.com/OneOfOne/xxhash v1.2.2/go.mod h1:HSdplMjZKSmBqAxg5vPj2TmRDmfkzw+cTzAElWljhcU=
 github.com/OpenPeeDeeP/depguard v1.0.1/go.mod h1:xsIw86fROiiwelg+jB2uM9PiKihMMmUx/1V+TNhjQvM=
@@ -26,8 +27,10 @@ github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSs
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/dgrijalva/jwt-go v3.2.0+incompatible/go.mod h1:E3ru+11k8xSBh+hMPgOLZmtrrCbhqsmaPHjLKYnJCaQ=
 github.com/dgryski/go-sip13 v0.0.0-20181026042036-e10d5fee7954/go.mod h1:vAd38F8PWV+bWy6jNmig1y/TA+kYO4g3RSRF0IAv0no=
+github.com/fatih/color v1.7.0 h1:DkWD4oS2D8LGGgTQ6IvwJJXSL5Vp2ffcQg58nFV38Ys=
 github.com/fatih/color v1.7.0/go.mod h1:Zm6kSWBoL9eyXnKyktHP6abPY2pDugNf5KwzbycvMj4=
 github.com/fatih/structtag v1.0.0/go.mod h1:IKitwq45uXL/yqi5mYghiD3w9H6eTOvI9vnk8tXMphA=
+github.com/fatih/structtag v1.2.0 h1:/OdNE99OxoI/PqaW/SuSK9uxxT3f/tcSZgon/ssNSx4=
 github.com/fatih/structtag v1.2.0/go.mod h1:mBJUNpUnHmRKrKlQQlmCrh5PuhftFbNv8Ys4/aAZl94=
 github.com/fsnotify/fsnotify v1.4.7/go.mod h1:jwhsz4b93w/PPRr/qN1Yymfu8t87LnFCMoQvtojpjFo=
 github.com/ghodss/yaml v1.0.0/go.mod h1:4dBDuWmgqj2HViK6kFavaiC9ZROes6MMH2rRYeMEF04=
@@ -117,17 +120,23 @@ github.com/magiconair/properties v1.8.0/go.mod h1:PppfXfuXeibc/6YijjN8zIbojt8czP
 github.com/magiconair/properties v1.8.1/go.mod h1:PppfXfuXeibc/6YijjN8zIbojt8czPbwD3XqdrwzmxQ=
 github.com/matoous/godox v0.0.0-20190911065817-5d6d842e92eb/go.mod h1:1BELzlh859Sh1c6+90blK8lbYy0kwQf1bYlBhBysy1s=
 github.com/mattn/go-colorable v0.1.2/go.mod h1:U0ppj6V5qS13XJ6of8GYAs25YV2eR4EVcfRqFIhoBtE=
+github.com/mattn/go-colorable v0.1.4 h1:snbPLB8fVfU9iwbbo30TPtbLRzwWu6aJS6Xh4eaaviA=
 github.com/mattn/go-colorable v0.1.4/go.mod h1:U0ppj6V5qS13XJ6of8GYAs25YV2eR4EVcfRqFIhoBtE=
 github.com/mattn/go-isatty v0.0.8/go.mod h1:Iq45c/XA43vh69/j3iqttzPXn0bhXyGjM0Hdxcsrc5s=
+github.com/mattn/go-isatty v0.0.9 h1:d5US/mDsogSGW37IV293h//ZFaeajb69h+EHFsv2xGg=
 github.com/mattn/go-isatty v0.0.9/go.mod h1:YNRxwqDuOph6SZLI9vUUz6OYw3QyUt7WiY2yME+cCiQ=
 github.com/mattn/go-runewidth v0.0.4/go.mod h1:LwmH8dsx7+W8Uxz3IHJYH5QSwggIsqBzpuz5H//U1FU=
+github.com/mattn/go-runewidth v0.0.7 h1:Ei8KR0497xHyKJPAv59M1dkC+rOZCMBJ+t3fZ+twI54=
 github.com/mattn/go-runewidth v0.0.7/go.mod h1:H031xJmbD/WCDINGzjvQ9THkh0rPKHF+m2gUSrubnMI=
 github.com/mattn/goveralls v0.0.2/go.mod h1:8d1ZMHsd7fW6IRPKQh46F2WRpyib5/X4FOpevwGNQEw=
 github.com/matttproud/golang_protobuf_extensions v1.0.1/go.mod h1:D8He9yQNgCq6Z5Ld7szi9bcBfOoFv/3dc6xSMkL2PC0=
 github.com/mgechev/dots v0.0.0-20181228164730-18fa4c4b71cc/go.mod h1:KQ7+USdGKfpPjXk4Ga+5XxQM4Lm4e3gAogrreFAYpOg=
+github.com/mgechev/dots v0.0.0-20190921121421-c36f7dcfbb81 h1:QASJXOGm2RZ5Ardbc86qNFvby9AqkLDibfChMtAg5QM=
 github.com/mgechev/dots v0.0.0-20190921121421-c36f7dcfbb81/go.mod h1:KQ7+USdGKfpPjXk4Ga+5XxQM4Lm4e3gAogrreFAYpOg=
 github.com/mgechev/revive v0.0.0-20190917153825-40564c5052ae/go.mod h1:37hJOqkogcmT5nmiriskuzkdJ/YhMlZwFSg87NDZbco=
+github.com/mgechev/revive v1.0.0 h1:CaN0UEsXgAovl5WB4yI7obZG+NhBh7HeEuQX11wVmTI=
 github.com/mgechev/revive v1.0.0/go.mod h1:Vwga5U/ducQXkYcbsNPMIOA1kFBVY1NBPs5Fa4Nfceg=
+github.com/mitchellh/go-homedir v1.1.0 h1:lukF9ziXFxDFPkA1vsr5zpc1XuPDn/wFntq5mG+4E0Y=
 github.com/mitchellh/go-homedir v1.1.0/go.mod h1:SfyaCUpYCn1Vlf4IUYiD9fPX4A5wJrkLzIz1N1q0pr0=
 github.com/mitchellh/go-ps v0.0.0-20190716172923-621e5597135b/go.mod h1:r1VsdOzOPt1ZSrGZWFoNhsAedKnEd6r9Np1+5blZCWk=
 github.com/mitchellh/mapstructure v1.1.2/go.mod h1:FVVH3fgwuzCH5S8UJGiWEs2h04kUh9fWfEaFds41c1Y=
@@ -137,6 +146,7 @@ github.com/nbutton23/zxcvbn-go v0.0.0-20180912185939-ae427f1e4c1d/go.mod h1:o96d
 github.com/nicksnyder/go-i18n v1.10.0/go.mod h1:HrK7VCrbOvQoUAQ7Vpy7i87N7JZZZ7R2xBGjv0j365Q=
 github.com/oklog/ulid v1.3.1/go.mod h1:CirwcVhetQ6Lv90oh/F+FBtV6XMibvdAFo93nm5qn4U=
 github.com/olekukonko/tablewriter v0.0.1/go.mod h1:vsDQFd/mU46D+Z4whnwzcISnGGzXWMclvtLoiIKAKIo=
+github.com/olekukonko/tablewriter v0.0.4 h1:vHD/YYe1Wolo78koG299f7V/VAS08c6IpCLn+Ejf/w8=
 github.com/olekukonko/tablewriter v0.0.4/go.mod h1:zq6QwlOf5SlnkVbMSr5EoBv3636FWnp+qbPhuoO21uA=
 github.com/onsi/ginkgo v1.6.0/go.mod h1:lLunBs/Ym6LB5Z9jYTR76FiuTmxDTDusOGeTQH+WWjE=
 github.com/onsi/ginkgo v1.10.1/go.mod h1:lLunBs/Ym6LB5Z9jYTR76FiuTmxDTDusOGeTQH+WWjE=
@@ -151,6 +161,8 @@ github.com/pingcap/failpoint v0.0.0-20190708053854-e7b1061e6e81 h1:g9j4cAoWE39lh
 github.com/pingcap/failpoint v0.0.0-20190708053854-e7b1061e6e81/go.mod h1:DNS3Qg7bEDhU6EXNHF+XSv/PGznQaMJ5FWvctpm6pQI=
 github.com/pingcap/failpoint v0.0.0-20191029060244-12f4ac2fd11d h1:F8vp38kTAckN+v8Jlc98uMBvKIzr1a+UhnLyVYn8Q5Q=
 github.com/pingcap/failpoint v0.0.0-20191029060244-12f4ac2fd11d/go.mod h1:DNS3Qg7bEDhU6EXNHF+XSv/PGznQaMJ5FWvctpm6pQI=
+github.com/pingcap/failpoint v0.0.0-20200210140405-f8f9fb234798 h1:6DMbRqPI1qzQ8N1xc3+nKY8IxSACd9VqQKkRVvbyoIg=
+github.com/pingcap/failpoint v0.0.0-20200210140405-f8f9fb234798/go.mod h1:DNS3Qg7bEDhU6EXNHF+XSv/PGznQaMJ5FWvctpm6pQI=
 github.com/pkg/errors v0.8.0/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pkg/errors v0.8.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
@@ -280,6 +292,7 @@ golang.org/x/tools v0.0.0-20190910044552-dd2b5c81c578/go.mod h1:b+2E5dAYhXwXZwtn
 golang.org/x/tools v0.0.0-20190930201159-7c411dea38b0/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
 golang.org/x/tools v0.0.0-20191010075000-0337d82405ff/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
 golang.org/x/tools v0.0.0-20191113232020-e2727e816f5a/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
+golang.org/x/tools v0.0.0-20191227053925-7b8e75db28f4 h1:Toz2IK7k8rbltAXwNAxKcn9OzqyNfMUhUNjz3sL0NMk=
 golang.org/x/tools v0.0.0-20191227053925-7b8e75db28f4/go.mod h1:TB2adYChydJhpapKDTa4BR/hXlZSLoq2Wpct/0txZ28=
 golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=