Performance improvements by re-using record buffer (#6622)

Avoid unnecessary pointer reference allocations
when not needed, for example

- *SelectFuncs{}
- *Row{}

cmd/object-handlers.go

@@ -33,6 +33,7 @@ import (
 
 	snappy "github.com/golang/snappy"
 	"github.com/gorilla/mux"
+	"github.com/klauspost/readahead"
 	miniogo "github.com/minio/minio-go"
 	"github.com/minio/minio/cmd/crypto"
 	"github.com/minio/minio/cmd/logger"
@@ -251,7 +252,10 @@ func (api objectAPIHandlers) SelectObjectContentHandler(w http.ResponseWriter, r
 		}
 	}
 
-	s3s, err := s3select.New(gr, objInfo.Size, selectReq)
+	reader := readahead.NewReader(gr)
+	defer reader.Close()
+
+	s3s, err := s3select.New(reader, objInfo.GetActualSize(), selectReq)
 	if err != nil {
 		writeErrorResponse(w, toAPIErrorCode(err), r.URL)
 		return
@@ -368,6 +372,7 @@ func (api objectAPIHandlers) GetObjectHandler(w http.ResponseWriter, r *http.Req
 		return
 	}
 	defer gr.Close()
+
 	objInfo := gr.ObjInfo
 
 	if objectAPI.IsEncryptionSupported() {

pkg/s3select/format/csv/csv.go

@@ -17,14 +17,12 @@
 package csv
 
 import (
-	"compress/bzip2"
 	"encoding/csv"
 	"encoding/xml"
 	"io"
 	"strconv"
 	"strings"
 
-	gzip "github.com/klauspost/pgzip"
 	"github.com/minio/minio/pkg/ioutil"
 	"github.com/minio/minio/pkg/s3select/format"
 )
@@ -89,28 +87,13 @@ type cinput struct {
 // Otherwise, the returned reader can be reliably consumed with Read().
 // until Read() return err.
 func New(opts *Options) (format.Select, error) {
-	myReader := opts.ReadFrom
-	var tempBytesScanned int64
-	tempBytesScanned = 0
-	switch opts.Compressed {
-	case "GZIP":
-		tempBytesScanned = opts.StreamSize
-		var err error
-		if myReader, err = gzip.NewReader(opts.ReadFrom); err != nil {
-			return nil, format.ErrTruncatedInput
-		}
-	case "BZIP2":
-		tempBytesScanned = opts.StreamSize
-		myReader = bzip2.NewReader(opts.ReadFrom)
-	}
-
 	// DelimitedReader treats custom record delimiter like `\r\n`,`\r`,`ab` etc and replaces it with `\n`.
-	normalizedReader := ioutil.NewDelimitedReader(myReader, []rune(opts.RecordDelimiter))
+	normalizedReader := ioutil.NewDelimitedReader(opts.ReadFrom, []rune(opts.RecordDelimiter))
 	reader := &cinput{
 		options: opts,
 		reader:  csv.NewReader(normalizedReader),
 	}
-	reader.stats.BytesScanned = tempBytesScanned
+	reader.stats.BytesScanned = opts.StreamSize
 	reader.stats.BytesProcessed = 0
 	reader.stats.BytesReturned = 0
 

pkg/s3select/format/json/json.go

@@ -17,13 +17,11 @@
 package json
 
 import (
-	"compress/bzip2"
 	"encoding/json"
 	"encoding/xml"
 	"io"
 
 	jsoniter "github.com/json-iterator/go"
-	gzip "github.com/klauspost/pgzip"
 	"github.com/minio/minio/pkg/s3select/format"
 )
 
@@ -75,26 +73,11 @@ type jinput struct {
 // Otherwise, the returned reader can be reliably consumed with jsonRead()
 // until jsonRead() returns nil.
 func New(opts *Options) (format.Select, error) {
-	myReader := opts.ReadFrom
-	var tempBytesScanned int64
-	tempBytesScanned = 0
-	switch opts.Compressed {
-	case "GZIP":
-		tempBytesScanned = opts.StreamSize
-		var err error
-		if myReader, err = gzip.NewReader(opts.ReadFrom); err != nil {
-			return nil, format.ErrTruncatedInput
-		}
-	case "BZIP2":
-		tempBytesScanned = opts.StreamSize
-		myReader = bzip2.NewReader(opts.ReadFrom)
-	}
-
 	reader := &jinput{
 		options: opts,
-		reader:  jsoniter.NewDecoder(myReader),
+		reader:  jsoniter.NewDecoder(opts.ReadFrom),
 	}
-	reader.stats.BytesScanned = tempBytesScanned
+	reader.stats.BytesScanned = opts.StreamSize
 	reader.stats.BytesProcessed = 0
 	reader.stats.BytesReturned = 0
 

pkg/s3select/helpers.go

@@ -490,17 +490,6 @@ func likeConvert(pattern string, record string) (bool, error) {
 	return true, nil
 }
 
-// TrimQuotes allows the following to occur select "name", we need to trim the
-// quotes to reference our map of columnNames.
-func trimQuotes(s string) string {
-	if len(s) >= 2 {
-		if c := s[len(s)-1]; s[0] == c && (c == '"') {
-			return s[1 : len(s)-1]
-		}
-	}
-	return s
-}
-
 // cleanCol cleans a column name from the parser so that the name is returned to
 // original.
 func cleanCol(myCol string, alias string) string {
@@ -641,7 +630,7 @@ func evaluateParserType(col *sqlparser.SQLVal) (interface{}, error) {
 
 // parseErrs is the function which handles all the errors that could occur
 // through use of function arguments such as column names in NULLIF
-func parseErrs(columnNames []string, whereClause interface{}, alias string, myFuncs *SelectFuncs, f format.Select) error {
+func parseErrs(columnNames []string, whereClause interface{}, alias string, myFuncs SelectFuncs, f format.Select) error {
 	// Below code cleans up column names.
 	processColumnNames(columnNames, alias, f)
 	if columnNames[0] != "*" {

pkg/s3select/input.go

@@ -18,6 +18,8 @@ package s3select
 
 import (
 	"bytes"
+	"compress/bzip2"
+	"compress/gzip"
 	"io"
 	"net/http"
 	"strings"
@@ -26,6 +28,8 @@ import (
 	"github.com/minio/minio/pkg/s3select/format"
 	"github.com/minio/minio/pkg/s3select/format/csv"
 	"github.com/minio/minio/pkg/s3select/format/json"
+
+	humanize "github.com/dustin/go-humanize"
 )
 
 const (
@@ -61,7 +65,16 @@ func cleanExpr(expr string) string {
 }
 
 // New - initialize new select format
-func New(gr io.Reader, size int64, req ObjectSelectRequest) (s3s format.Select, err error) {
+func New(reader io.Reader, size int64, req ObjectSelectRequest) (s3s format.Select, err error) {
+	switch req.InputSerialization.CompressionType {
+	case SelectCompressionGZIP:
+		if reader, err = gzip.NewReader(reader); err != nil {
+			return nil, format.ErrTruncatedInput
+		}
+	case SelectCompressionBZIP:
+		reader = bzip2.NewReader(reader)
+	}
+
 	//  Initializating options for CSV
 	if req.InputSerialization.CSV != nil {
 		if req.OutputSerialization.CSV.FieldDelimiter == "" {
@@ -79,7 +92,7 @@ func New(gr io.Reader, size int64, req ObjectSelectRequest) (s3s format.Select,
 			FieldDelimiter:       req.InputSerialization.CSV.FieldDelimiter,
 			Comments:             req.InputSerialization.CSV.Comments,
 			Name:                 "S3Object", // Default table name for all objects
-			ReadFrom:             gr,
+			ReadFrom:             reader,
 			Compressed:           string(req.InputSerialization.CompressionType),
 			Expression:           cleanExpr(req.Expression),
 			OutputFieldDelimiter: req.OutputSerialization.CSV.FieldDelimiter,
@@ -91,7 +104,7 @@ func New(gr io.Reader, size int64, req ObjectSelectRequest) (s3s format.Select,
 		//  Initializating options for JSON
 		s3s, err = json.New(&json.Options{
 			Name:       "S3Object", // Default table name for all objects
-			ReadFrom:   gr,
+			ReadFrom:   reader,
 			Compressed: string(req.InputSerialization.CompressionType),
 			Expression: cleanExpr(req.Expression),
 			StreamSize: size,
@@ -106,8 +119,8 @@ func New(gr io.Reader, size int64, req ObjectSelectRequest) (s3s format.Select,
 // response writer in a streaming fashion so that the client can actively use
 // the results before the query is finally finished executing. The
 func Execute(writer io.Writer, f format.Select) error {
-	myRow := make(chan *Row)
+	myRow := make(chan Row, 1000)
-	curBuf := bytes.NewBuffer(make([]byte, 1000000))
+	curBuf := bytes.NewBuffer(make([]byte, humanize.MiByte))
 	curBuf.Reset()
 	progressTicker := time.NewTicker(progressTime)
 	continuationTimer := time.NewTimer(continuationTime)
@@ -115,13 +128,11 @@ func Execute(writer io.Writer, f format.Select) error {
 	defer continuationTimer.Stop()
 
 	go runSelectParser(f, myRow)
-
 	for {
 		select {
 		case row, ok := <-myRow:
 			if ok && row.err != nil {
-				errorMessage := writeErrorMessage(row.err, curBuf)
+				_, err := writeErrorMessage(row.err, curBuf).WriteTo(writer)
-				_, err := errorMessage.WriteTo(writer)
 				flusher, okFlush := writer.(http.Flusher)
 				if okFlush {
 					flusher.Flush()
@@ -133,8 +144,7 @@ func Execute(writer io.Writer, f format.Select) error {
 				close(myRow)
 				return nil
 			} else if ok {
-				message := writeRecordMessage(row.record, curBuf)
+				_, err := writeRecordMessage(row.record, curBuf).WriteTo(writer)
-				_, err := message.WriteTo(writer)
 				flusher, okFlush := writer.(http.Flusher)
 				if okFlush {
 					flusher.Flush()
@@ -153,8 +163,7 @@ func Execute(writer io.Writer, f format.Select) error {
 				if err != nil {
 					return err
 				}
-				statMessage := writeStatMessage(statPayload, curBuf)
+				_, err = writeStatMessage(statPayload, curBuf).WriteTo(writer)
-				_, err = statMessage.WriteTo(writer)
 				flusher, ok := writer.(http.Flusher)
 				if ok {
 					flusher.Flush()
@@ -163,8 +172,7 @@ func Execute(writer io.Writer, f format.Select) error {
 					return err
 				}
 				curBuf.Reset()
-				message := writeEndMessage(curBuf)
+				_, err = writeEndMessage(curBuf).WriteTo(writer)
-				_, err = message.WriteTo(writer)
 				flusher, ok = writer.(http.Flusher)
 				if ok {
 					flusher.Flush()
@@ -182,8 +190,7 @@ func Execute(writer io.Writer, f format.Select) error {
 				if err != nil {
 					return err
 				}
-				progressMessage := writeProgressMessage(progressPayload, curBuf)
+				_, err = writeProgressMessage(progressPayload, curBuf).WriteTo(writer)
-				_, err = progressMessage.WriteTo(writer)
 				flusher, ok := writer.(http.Flusher)
 				if ok {
 					flusher.Flush()
@@ -194,8 +201,7 @@ func Execute(writer io.Writer, f format.Select) error {
 				curBuf.Reset()
 			}
 		case <-continuationTimer.C:
-			message := writeContinuationMessage(curBuf)
+			_, err := writeContinuationMessage(curBuf).WriteTo(writer)
-			_, err := message.WriteTo(writer)
 			flusher, ok := writer.(http.Flusher)
 			if ok {
 				flusher.Flush()

pkg/s3select/select.go

@@ -36,13 +36,12 @@ type SelectFuncs struct {
 
 // RunSqlParser allows us to easily bundle all the functions from above and run
 // them in the appropriate order.
-func runSelectParser(f format.Select, myRow chan *Row) {
+func runSelectParser(f format.Select, myRow chan Row) {
 	reqCols, alias, myLimit, whereClause, aggFunctionNames, myFuncs, myErr := ParseSelect(f)
 	if myErr != nil {
-		rowStruct := &Row{
+		myRow <- Row{
 			err: myErr,
 		}
-		myRow <- rowStruct
 		return
 	}
 	processSelectReq(reqCols, alias, whereClause, myLimit, aggFunctionNames, myRow, myFuncs, f)
@@ -52,19 +51,18 @@ func runSelectParser(f format.Select, myRow chan *Row) {
 // ParseSelect parses the SELECT expression, and effectively tokenizes it into
 // its separate parts. It returns the requested column names,alias,limit of
 // records, and the where clause.
-func ParseSelect(f format.Select) ([]string, string, int64, interface{}, []string, *SelectFuncs, error) {
+func ParseSelect(f format.Select) ([]string, string, int64, interface{}, []string, SelectFuncs, error) {
-	// return columnNames, alias, limitOfRecords, whereclause,coalStore, nil
+	var sFuncs = SelectFuncs{}
-
-	stmt, err := sqlparser.Parse(cleanExpr(f.Expression()))
-	// TODO Maybe can parse their errors a bit to return some more of the s3 errors
-	if err != nil {
-		return nil, "", 0, nil, nil, nil, ErrLexerInvalidChar
-	}
-
 	var whereClause interface{}
 	var alias string
 	var limit int64
-	myFuncs := &SelectFuncs{}
+
+	stmt, err := sqlparser.Parse(f.Expression())
+	// TODO Maybe can parse their errors a bit to return some more of the s3 errors
+	if err != nil {
+		return nil, "", 0, nil, nil, sFuncs, ErrLexerInvalidChar
+	}
+
 	switch stmt := stmt.(type) {
 	case *sqlparser.Select:
 		// evaluates the where clause
@@ -95,26 +93,26 @@ func ParseSelect(f format.Select) ([]string, string, int64, interface{}, []strin
 							case *sqlparser.StarExpr:
 								columnNames[0] = "*"
 								if smallerexpr.Name.CompliantName() != "count" {
-									return nil, "", 0, nil, nil, nil, ErrParseUnsupportedCallWithStar
+									return nil, "", 0, nil, nil, sFuncs, ErrParseUnsupportedCallWithStar
 								}
 							case *sqlparser.AliasedExpr:
 								switch col := tempagg.Expr.(type) {
 								case *sqlparser.BinaryExpr:
-									return nil, "", 0, nil, nil, nil, ErrParseNonUnaryAgregateFunctionCall
+									return nil, "", 0, nil, nil, sFuncs, ErrParseNonUnaryAgregateFunctionCall
 								case *sqlparser.ColName:
 									columnNames[i] = col.Name.CompliantName()
 								}
 							}
 							// Case to deal with if COALESCE was used..
 						} else if supportedFunc(smallerexpr.Name.CompliantName()) {
-							if myFuncs.funcExpr == nil {
+							if sFuncs.funcExpr == nil {
-								myFuncs.funcExpr = make([]*sqlparser.FuncExpr, len(stmt.SelectExprs))
+								sFuncs.funcExpr = make([]*sqlparser.FuncExpr, len(stmt.SelectExprs))
-								myFuncs.index = make([]int, len(stmt.SelectExprs))
+								sFuncs.index = make([]int, len(stmt.SelectExprs))
 							}
-							myFuncs.funcExpr[i] = smallerexpr
+							sFuncs.funcExpr[i] = smallerexpr
-							myFuncs.index[i] = i
+							sFuncs.index[i] = i
 						} else {
-							return nil, "", 0, nil, nil, nil, ErrUnsupportedSQLOperation
+							return nil, "", 0, nil, nil, sFuncs, ErrUnsupportedSQLOperation
 						}
 					case *sqlparser.ColName:
 						columnNames[i] = smallerexpr.Name.CompliantName()
@@ -129,7 +127,7 @@ func ParseSelect(f format.Select) ([]string, string, int64, interface{}, []strin
 			for i := 0; i < len(stmt.From); i++ {
 				switch smallerexpr := stmt.From[i].(type) {
 				case *sqlparser.JoinTableExpr:
-					return nil, "", 0, nil, nil, nil, ErrParseMalformedJoin
+					return nil, "", 0, nil, nil, sFuncs, ErrParseMalformedJoin
 				case *sqlparser.AliasedTableExpr:
 					alias = smallerexpr.As.CompliantName()
 					if alias == "" {
@@ -147,23 +145,23 @@ func ParseSelect(f format.Select) ([]string, string, int64, interface{}, []strin
 			}
 		}
 		if stmt.GroupBy != nil {
-			return nil, "", 0, nil, nil, nil, ErrParseUnsupportedLiteralsGroupBy
+			return nil, "", 0, nil, nil, sFuncs, ErrParseUnsupportedLiteralsGroupBy
 		}
 		if stmt.OrderBy != nil {
-			return nil, "", 0, nil, nil, nil, ErrParseUnsupportedToken
+			return nil, "", 0, nil, nil, sFuncs, ErrParseUnsupportedToken
 		}
-		if err := parseErrs(columnNames, whereClause, alias, myFuncs, f); err != nil {
+		if err := parseErrs(columnNames, whereClause, alias, sFuncs, f); err != nil {
-			return nil, "", 0, nil, nil, nil, err
+			return nil, "", 0, nil, nil, sFuncs, err
 		}
-		return columnNames, alias, limit, whereClause, functionNames, myFuncs, nil
+		return columnNames, alias, limit, whereClause, functionNames, sFuncs, nil
 	}
-	return nil, "", 0, nil, nil, nil, nil
+	return nil, "", 0, nil, nil, sFuncs, nil
 }
 
 // This is the main function, It goes row by row and for records which validate
 // the where clause it currently prints the appropriate row given the requested
 // columns.
-func processSelectReq(reqColNames []string, alias string, whereClause interface{}, limitOfRecords int64, functionNames []string, myRow chan *Row, myFunc *SelectFuncs, f format.Select) {
+func processSelectReq(reqColNames []string, alias string, whereClause interface{}, limitOfRecords int64, functionNames []string, myRow chan Row, myFunc SelectFuncs, f format.Select) {
 	counter := -1
 	var columns []string
 	filtrCount := 0
@@ -183,18 +181,16 @@ func processSelectReq(reqColNames []string, alias string, whereClause interface{
 	for {
 		record, err := f.Read()
 		if err != nil {
-			rowStruct := &Row{
+			myRow <- Row{
 				err: err,
 			}
-			myRow <- rowStruct
 			return
 		}
 		if record == nil {
 			if functionFlag {
-				rowStruct := &Row{
+				myRow <- Row{
 					record: aggFuncToStr(myAggVals, f) + "\n",
 				}
-				myRow <- rowStruct
 			}
 			close(myRow)
 			return
@@ -210,10 +206,9 @@ func processSelectReq(reqColNames []string, alias string, whereClause interface{
 				myErr = ErrMissingHeaders
 			}
 			if myErr != nil {
-				rowStruct := &Row{
+				myRow <- Row{
 					err: myErr,
 				}
-				myRow <- rowStruct
 				return
 			}
 		} else if counter == -1 && len(f.Header()) > 0 {
@@ -232,28 +227,26 @@ func processSelectReq(reqColNames []string, alias string, whereClause interface{
 		// The call to the where function clause,ensures that the rows we print match our where clause.
 		condition, myErr := matchesMyWhereClause(record, alias, whereClause)
 		if myErr != nil {
-			rowStruct := &Row{
+			myRow <- Row{
 				err: myErr,
 			}
-			myRow <- rowStruct
 			return
 		}
 		if condition {
 			// if its an asterix we just print everything in the row
 			if reqColNames[0] == "*" && functionNames[0] == "" {
-				var row *Row
+				var row Row
 				switch f.Type() {
 				case format.CSV:
-					row = &Row{
+					row = Row{
 						record: strings.Join(convertToSlice(columnsMap, record, string(out)), f.OutputFieldDelimiter()) + "\n",
 					}
 				case format.JSON:
-					row = &Row{
+					row = Row{
 						record: string(out) + "\n",
 					}
 				}
 				myRow <- row
-
 			} else if alias != "" {
 				// This is for dealing with the case of if we have to deal with a
 				// request for a column with an index e.g A_1.
@@ -269,16 +262,14 @@ func processSelectReq(reqColNames []string, alias string, whereClause interface{
 						// retrieve the correct part of the row.
 						myQueryRow, myErr := processColNameIndex(string(out), reqColNames, columns, f)
 						if myErr != nil {
-							rowStruct := &Row{
+							myRow <- Row{
 								err: myErr,
 							}
-							myRow <- rowStruct
 							return
 						}
-						rowStruct := &Row{
+						myRow <- Row{
 							record: myQueryRow + "\n",
 						}
-						myRow <- rowStruct
 					}
 				} else {
 					// This code does aggregation if we were provided column names in the
@@ -292,16 +283,14 @@ func processSelectReq(reqColNames []string, alias string, whereClause interface{
 						// names rather than indices.
 						myQueryRow, myErr := processColNameLiteral(string(out), reqColNames, myFunc, f)
 						if myErr != nil {
-							rowStruct := &Row{
+							myRow <- Row{
 								err: myErr,
 							}
-							myRow <- rowStruct
 							return
 						}
-						rowStruct := &Row{
+						myRow <- Row{
 							record: myQueryRow + "\n",
 						}
-						myRow <- rowStruct
 					}
 				}
 			}
@@ -357,7 +346,7 @@ func processColNameIndex(record string, reqColNames []string, columns []string,
 
 // processColNameLiteral is the function which creates the row for an name based
 // query.
-func processColNameLiteral(record string, reqColNames []string, myFunc *SelectFuncs, f format.Select) (string, error) {
+func processColNameLiteral(record string, reqColNames []string, myFunc SelectFuncs, f format.Select) (string, error) {
 	row := make([]string, len(reqColNames))
 	for i := 0; i < len(reqColNames); i++ {
 		// this is the case to deal with COALESCE.

vendor/github.com/klauspost/readahead/LICENSE

@@ -0,0 +1,22 @@
+The MIT License (MIT)
+
+Copyright (c) 2015 Klaus Post
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+

vendor/github.com/klauspost/readahead/README.md

@@ -0,0 +1,59 @@
+# readahead
+Asynchronous read-ahead for Go readers
+
+This package will allow you to add readhead to any reader. This means a separate goroutine will perform reads from your upstream reader, so you can request from this reader without delay.
+
+This is helpful for splitting an input stream into concurrent processing, and also helps smooth out **bursts** of input or output.
+
+This should be fully transparent, except that once an error has been returned from the Reader, it will not recover. A panic will be caught and returned as an error.
+
+The readahead object also fulfills the [`io.WriterTo`](https://golang.org/pkg/io/#WriterTo) interface, which is likely to speed up `io.Copy` and other code that use the interface.
+
+See an introduction: [An Async Read-ahead Package for Go](https://blog.klauspost.com/an-async-read-ahead-package-for-go/)
+
+[![GoDoc][1]][2] [![Build Status][3]][4]
+
+[1]: https://godoc.org/github.com/klauspost/readahead?status.svg
+[2]: https://godoc.org/github.com/klauspost/readahead
+[3]: https://travis-ci.org/klauspost/readahead.svg
+[4]: https://travis-ci.org/klauspost/readahead
+
+# usage
+
+To get the package use `go get -u github.com/klauspost/readahead`.
+
+Here is a simple example that does file copy. Error handling has been omitted for brevity.
+```Go
+input, _ := os.Open("input.txt")
+output, _ := os.Create("output.txt")
+defer input.Close()
+defer output.Close()
+
+// Create a read-ahead Reader with default settings
+ra := readahead.NewReader(input)
+defer ra.Close()
+
+// Copy the content to our output
+_, _ = io.Copy(output, ra)
+```
+
+# settings
+
+You can finetune the read-ahead for your specific use case, and adjust the number of buffers and the size of each buffer.
+
+The default the size of each buffer is 1MB, and there are 4 buffers. Do not make your buffers too small since there is a small overhead for passing buffers between goroutines. Other than that you are free to experiment with buffer sizes.
+
+# contributions
+
+On this project contributions in terms of new features is limited to:
+
+* Features that are widely usable and
+* Features that have extensive tests
+
+This package is meant to be simple and stable, so therefore these strict requirements.
+
+The only feature I have considered is supporting the `io.Seeker` interface. I currently do not plan to add it myself, but if you can show a clean and well-tested way to implementing it, I will consider to merge it. If not, I will be happy to link to it.
+
+# license
+
+This package is released under the MIT license. See the supplied LICENSE file for more info.

vendor/github.com/klauspost/readahead/reader.go

@@ -0,0 +1,282 @@
+// Copyright (c) 2015 Klaus Post, released under MIT License. See LICENSE file.
+
+// The readahead package will do asynchronous read-ahead from an input io.Reader
+// and make the data available as an io.Reader.
+//
+// This should be fully transparent, except that once an error
+// has been returned from the Reader, it will not recover.
+//
+// The readahead object also fulfills the io.WriterTo interface, which
+// is likely to speed up copies.
+//
+// Package home: https://github.com/klauspost/readahead
+//
+package readahead
+
+import (
+	"fmt"
+	"io"
+)
+
+type reader struct {
+	in      io.Reader     // Input reader
+	closer  io.Closer     // Optional closer
+	ready   chan *buffer  // Buffers ready to be handed to the reader
+	reuse   chan *buffer  // Buffers to reuse for input reading
+	exit    chan struct{} // Closes when finished
+	buffers int           // Number of buffers
+	err     error         // If an error has occurred it is here
+	cur     *buffer       // Current buffer being served
+	exited  chan struct{} // Channel is closed been the async reader shuts down
+}
+
+// New returns a reader that will asynchronously read from
+// the supplied reader into 4 buffers of 1MB each.
+//
+// It will start reading from the input at once, maybe even before this
+// function has returned.
+//
+// The input can be read from the returned reader.
+// When done use Close() to release the buffers.
+func NewReader(rd io.Reader) io.ReadCloser {
+	if rd == nil {
+		return nil
+	}
+
+	ret, err := NewReaderSize(rd, 4, 1<<20)
+
+	// Should not be possible to trigger from other packages.
+	if err != nil {
+		panic("unexpected error:" + err.Error())
+	}
+	return ret
+}
+
+// New returns a reader that will asynchronously read from
+// the supplied reader into 4 buffers of 1MB each.
+//
+// It will start reading from the input at once, maybe even before this
+// function has returned.
+//
+// The input can be read from the returned reader.
+// When done use Close() to release the buffers,
+// which will also close the supplied closer.
+func NewReadCloser(rd io.ReadCloser) io.ReadCloser {
+	if rd == nil {
+		return nil
+	}
+
+	ret, err := NewReadCloserSize(rd, 4, 1<<20)
+
+	// Should not be possible to trigger from other packages.
+	if err != nil {
+		panic("unexpected error:" + err.Error())
+	}
+	return ret
+}
+
+// NewReaderSize returns a reader with a custom number of buffers and size.
+// buffers is the number of queued buffers and size is the size of each
+// buffer in bytes.
+func NewReaderSize(rd io.Reader, buffers, size int) (io.ReadCloser, error) {
+	if size <= 0 {
+		return nil, fmt.Errorf("buffer size too small")
+	}
+	if buffers <= 0 {
+		return nil, fmt.Errorf("number of buffers too small")
+	}
+	if rd == nil {
+		return nil, fmt.Errorf("nil input reader supplied")
+	}
+	a := &reader{}
+	a.init(rd, buffers, size)
+	return a, nil
+}
+
+// NewReadCloserSize returns a reader with a custom number of buffers and size.
+// buffers is the number of queued buffers and size is the size of each
+// buffer in bytes.
+func NewReadCloserSize(rc io.ReadCloser, buffers, size int) (io.ReadCloser, error) {
+	if size <= 0 {
+		return nil, fmt.Errorf("buffer size too small")
+	}
+	if buffers <= 0 {
+		return nil, fmt.Errorf("number of buffers too small")
+	}
+	if rc == nil {
+		return nil, fmt.Errorf("nil input reader supplied")
+	}
+	a := &reader{closer: rc}
+	a.init(rc, buffers, size)
+	return a, nil
+}
+
+// initialize the reader
+func (a *reader) init(rd io.Reader, buffers, size int) {
+	a.in = rd
+	a.ready = make(chan *buffer, buffers)
+	a.reuse = make(chan *buffer, buffers)
+	a.exit = make(chan struct{}, 0)
+	a.exited = make(chan struct{}, 0)
+	a.buffers = buffers
+	a.cur = nil
+
+	// Create buffers
+	for i := 0; i < buffers; i++ {
+		a.reuse <- newBuffer(size)
+	}
+
+	// Start async reader
+	go func() {
+		// Ensure that when we exit this is signalled.
+		defer close(a.exited)
+		for {
+			select {
+			case b := <-a.reuse:
+				err := b.read(a.in)
+				a.ready <- b
+				if err != nil {
+					close(a.ready)
+					return
+				}
+			case <-a.exit:
+				return
+			}
+		}
+	}()
+}
+
+// fill will check if the current buffer is empty and fill it if it is.
+// If an error was returned at the end of the current buffer it is returned.
+func (a *reader) fill() (err error) {
+	if a.cur.isEmpty() {
+		if a.cur != nil {
+			a.reuse <- a.cur
+			a.cur = nil
+		}
+		b, ok := <-a.ready
+		if !ok {
+			return a.err
+		}
+		a.cur = b
+	}
+	return nil
+}
+
+// Read will return the next available data.
+func (a *reader) Read(p []byte) (n int, err error) {
+	// Swap buffer and maybe return error
+	err = a.fill()
+	if err != nil {
+		return 0, err
+	}
+
+	// Copy what we can
+	n = copy(p, a.cur.buffer())
+	a.cur.inc(n)
+
+	// If at end of buffer, return any error, if present
+	if a.cur.isEmpty() {
+		a.err = a.cur.err
+		return n, a.err
+	}
+	return n, nil
+}
+
+// WriteTo writes data to w until there's no more data to write or when an error occurs.
+// The return value n is the number of bytes written.
+// Any error encountered during the write is also returned.
+func (a *reader) WriteTo(w io.Writer) (n int64, err error) {
+	n = 0
+	for {
+		err = a.fill()
+		if err != nil {
+			return n, err
+		}
+		n2, err := w.Write(a.cur.buffer())
+		a.cur.inc(n2)
+		n += int64(n2)
+		if err != nil {
+			return n, err
+		}
+		if a.cur.err != nil {
+			// io.Writer should return nil if we are at EOF.
+			if a.cur.err == io.EOF {
+				a.err = a.cur.err
+				return n, nil
+			}
+			a.err = a.cur.err
+			return n, a.cur.err
+		}
+	}
+}
+
+// Close will ensure that the underlying async reader is shut down.
+// It will also close the input supplied on newAsyncReader.
+func (a *reader) Close() (err error) {
+	select {
+	case <-a.exited:
+	case a.exit <- struct{}{}:
+		<-a.exited
+	}
+	if a.closer != nil {
+		// Only call once
+		c := a.closer
+		a.closer = nil
+		return c.Close()
+	}
+	return nil
+}
+
+// Internal buffer representing a single read.
+// If an error is present, it must be returned
+// once all buffer content has been served.
+type buffer struct {
+	buf    []byte
+	err    error
+	offset int
+	size   int
+}
+
+func newBuffer(size int) *buffer {
+	return &buffer{buf: make([]byte, size), err: nil, size: size}
+}
+
+// isEmpty returns true is offset is at end of
+// buffer, or if the buffer is nil
+func (b *buffer) isEmpty() bool {
+	if b == nil {
+		return true
+	}
+	if len(b.buf)-b.offset <= 0 {
+		return true
+	}
+	return false
+}
+
+// read into start of the buffer from the supplied reader,
+// resets the offset and updates the size of the buffer.
+// Any error encountered during the read is returned.
+func (b *buffer) read(rd io.Reader) (err error) {
+	defer func() {
+		if r := recover(); r != nil {
+			err = fmt.Errorf("panic reading: %v", r)
+			b.err = err
+		}
+	}()
+	var n int
+	n, b.err = rd.Read(b.buf[0:b.size])
+	b.buf = b.buf[0:n]
+	b.offset = 0
+	return b.err
+}
+
+// Return the buffer at current offset
+func (b *buffer) buffer() []byte {
+	return b.buf[b.offset:]
+}
+
+// inc will increment the read offset
+func (b *buffer) inc(n int) {
+	b.offset += n
+}

vendor/vendor.json

@@ -562,6 +562,12 @@
 			"revision": "90b2c57fba35a1dd05cb40f9200722763808d99b",
 			"revisionTime": "2018-06-06T15:09:39Z"
 		},
+		{
+			"checksumSHA1": "/8VtN8HUS0G235mhqfj2gRMi9Eg=",
+			"path": "github.com/klauspost/readahead",
+			"revision": "7f90b27d81113b71920c55b7a73a071dc81bdfd8",
+			"revisionTime": "2017-10-07T12:43:06Z"
+		},
 		{
 			"checksumSHA1": "ehsrWipiGIWqa4To8TmelIx06vI=",
 			"path": "github.com/klauspost/reedsolomon",