Optimize string processing in select (#6593)

Reduce allocations during string concatenation and simplify some
processing code.

pkg/s3select/helpers.go

@@ -55,8 +55,8 @@ func stringInSlice(x string, list []string) bool {
 
 // This function returns the index of a string in a list
 func stringIndex(a string, list []string) int {
-	for i := range list {
-		if list[i] == a {
+	for i, v := range list {
+		if v == a {
 			return i
 		}
 	}
@@ -65,10 +65,8 @@ func stringIndex(a string, list []string) int {
 
 // Returns a true or false, whether a string can be represented as an int.
 func representsInt(s string) bool {
-	if _, err := strconv.Atoi(s); err == nil {
-		return true
-	}
-	return false
+	_, err := strconv.Atoi(s)
+	return err == nil
 }
 
 // The function below processes the where clause into an acutal boolean given a
@@ -236,16 +234,16 @@ func checkValidOperator(operator string) error {
 }
 
 // checkStringType converts the value from the csv to the appropriate one.
-func checkStringType(myTblVal string) interface{} {
-	myInt, isInt := strconv.Atoi(myTblVal)
-	myFloat, isFloat := strconv.ParseFloat(myTblVal, 64)
-	if isInt == nil {
-		return myInt
-	} else if isFloat == nil {
-		return myFloat
-	} else {
-		return myTblVal
+func checkStringType(tblVal string) interface{} {
+	intVal, err := strconv.Atoi(tblVal)
+	if err == nil {
+		return intVal
 	}
+	floatVal, err := strconv.ParseFloat(tblVal, 64)
+	if err == nil {
+		return floatVal
+	}
+	return tblVal
 }
 
 // stringEval is for evaluating the state of string comparison.
@@ -627,31 +625,6 @@ func (reader *Input) whereClauseNameErrs(whereClause interface{}, alias string)
 	return nil
 }
 
-// qualityCheck ensures the row has enough separators.
-func qualityCheck(row string, amountOfSep int, sep string) string {
-	for i := 0; i < amountOfSep; i++ {
-		row = row + sep
-	}
-	return row
-}
-
-// writeRow helps to write the row regardless of how many entries.
-func writeRow(myRow string, myEntry string, delimiter string, numOfReqCols int) string {
-	if myEntry == "" && len(myRow) == 0 && numOfReqCols == 1 {
-		return myEntry
-	}
-	if myEntry == "" && len(myRow) == 0 {
-		return myEntry + delimiter
-	}
-	if len(myRow) == 1 && myRow[0] == ',' {
-		return myRow + myEntry
-	}
-	if len(myRow) == 0 {
-		return myEntry
-	}
-	return myRow + delimiter + myEntry
-}
-
 // colNameErrs is a function which makes sure that the headers are requested are
 // present in the file otherwise it throws an error.
 func (reader *Input) colNameErrs(columnNames []string) error {
@@ -677,24 +650,23 @@ func (reader *Input) colNameErrs(columnNames []string) error {
 }
 
 // aggFuncToStr converts an array of floats into a properly formatted string.
-func (reader *Input) aggFuncToStr(myAggVals []float64) string {
-	var myRow string
-	var aggregateval string
-	if myAggVals[0] == math.Trunc(myAggVals[0]) {
-		myRow = strconv.FormatInt(int64(myAggVals[0]), 10)
-	} else {
-		myRow = strconv.FormatFloat(myAggVals[0], 'f', 6, 64)
-	}
-
-	for i := 1; i < len(myAggVals); i++ {
-		if myAggVals[i] == math.Trunc(myAggVals[i]) {
-			aggregateval = strconv.FormatInt(int64(myAggVals[i]), 10)
-		} else {
-			aggregateval = strconv.FormatFloat(myAggVals[i], 'f', 6, 64)
+func (reader *Input) aggFuncToStr(aggVals []float64) string {
+	// Define a number formatting function
+	numToStr := func(f float64) string {
+		if f == math.Trunc(f) {
+			return strconv.FormatInt(int64(f), 10)
 		}
-		myRow = myRow + reader.options.OutputFieldDelimiter + aggregateval
+		return strconv.FormatFloat(f, 'f', 6, 64)
+	}
+
+	// Display all whole numbers in aggVals as integers
+	vals := make([]string, len(aggVals))
+	for i, v := range aggVals {
+		vals[i] = numToStr(v)
 	}
-	return myRow
+
+	// Intersperse field delimiter
+	return strings.Join(vals, reader.options.OutputFieldDelimiter)
 }
 
 // checkForDuplicates ensures we do not have an ambigious column name.

pkg/s3select/select.go

@@ -284,11 +284,7 @@ func (reader *Input) processSelectReq(reqColNames []string, alias string, whereC
 
 // printAsterix helps to print out the entire row if an asterix is used.
 func (reader *Input) printAsterix(record []string) string {
-	myRow := record[0]
-	for i := 1; i < len(record); i++ {
-		myRow = myRow + reader.options.OutputFieldDelimiter + record[i]
-	}
-	return myRow
+	return strings.Join(record, reader.options.OutputFieldDelimiter)
 }
 
 // processColumnNames is a function which allows for cleaning of column names.
@@ -304,7 +300,7 @@ func (reader *Input) processColumnNames(reqColNames []string, alias string) erro
 // processColNameIndex is the function which creates the row for an index based
 // query.
 func (reader *Input) processColNameIndex(record []string, reqColNames []string, columns []string) (string, error) {
-	myRow := ""
+	row := make([]string, len(reqColNames))
 	for i := 0; i < len(reqColNames); i++ {
 		// COALESCE AND NULLIF do not support index based access.
 		if reqColNames[0] == "0" {
@@ -312,54 +308,48 @@ func (reader *Input) processColNameIndex(record []string, reqColNames []string,
 		}
 		// Subtract 1 because AWS Indexing is not 0 based, it starts at 1.
 		mytempindex, err := strconv.Atoi(reqColNames[i])
+		if err != nil {
+			return "", ErrMissingHeaders
+		}
 		mytempindex = mytempindex - 1
 		if mytempindex > len(columns) {
 			return "", ErrInvalidColumnIndex
 		}
-		myRow = writeRow(myRow, record[mytempindex], reader.options.OutputFieldDelimiter, len(reqColNames))
-		if err != nil {
-			return "", ErrMissingHeaders
-		}
+		row[i] = record[mytempindex]
 	}
-	if len(myRow) > 1000000 {
+	rowStr := strings.Join(row, reader.options.OutputFieldDelimiter)
+	if len(rowStr) > 1000000 {
 		return "", ErrOverMaxRecordSize
 	}
-	if strings.Count(myRow, reader.options.OutputFieldDelimiter) != len(reqColNames)-1 {
-		myRow = qualityCheck(myRow, len(reqColNames)-1-strings.Count(myRow, reader.options.OutputFieldDelimiter), reader.options.OutputFieldDelimiter)
-	}
-	return myRow, nil
+	return rowStr, nil
 }
 
 // processColNameLiteral is the function which creates the row for an name based
 // query.
 func (reader *Input) processColNameLiteral(record []string, reqColNames []string, columns []string, columnsMap map[string]int, myFunc *SelectFuncs) (string, error) {
-	myRow := ""
+	row := make([]string, len(reqColNames))
 	for i := 0; i < len(reqColNames); i++ {
 		// this is the case to deal with COALESCE.
 		if reqColNames[i] == "" && isValidFunc(myFunc.index, i) {
-			myVal := evaluateFuncExpr(myFunc.funcExpr[i], "", record, columnsMap)
-			myRow = writeRow(myRow, myVal, reader.options.OutputFieldDelimiter, len(reqColNames))
+			row[i] = evaluateFuncExpr(myFunc.funcExpr[i], "", record, columnsMap)
 			continue
 		}
 		myTempIndex, notFound := columnsMap[trimQuotes(reqColNames[i])]
 		if !notFound {
 			return "", ErrMissingHeaders
 		}
-		myRow = writeRow(myRow, record[myTempIndex], reader.options.OutputFieldDelimiter, len(reqColNames))
+		row[i] = record[myTempIndex]
 	}
-	if len(myRow) > 1000000 {
+	rowStr := strings.Join(row, reader.options.OutputFieldDelimiter)
+	if len(rowStr) > 1000000 {
 		return "", ErrOverMaxRecordSize
 	}
-	if strings.Count(myRow, reader.options.OutputFieldDelimiter) != len(reqColNames)-1 {
-		myRow = qualityCheck(myRow, len(reqColNames)-1-strings.Count(myRow, reader.options.OutputFieldDelimiter), reader.options.OutputFieldDelimiter)
-	}
-	return myRow, nil
-
+	return rowStr, nil
 }
 
-// aggregationFunctions is a function which performs the actual aggregation
-// methods on the given row, it uses an array defined the the main parsing
-// function to keep track of values.
+// aggregationFunctions performs the actual aggregation methods on the
+// given row, it uses an array defined for the main parsing function
+// to keep track of values.
 func aggregationFunctions(counter int, filtrCount int, myAggVals []float64, columnsMap map[string]int, storeReqCols []string, storeFunctions []string, record []string) error {
 	for i := 0; i < len(storeFunctions); i++ {
 		if storeFunctions[i] == "" {