Use maps.Keys where applicable (#821)

Also pass map size hints in a few more places

flow/connectors/bigquery/merge_statement_generator.go

@@ -94,10 +94,13 @@ func (m *mergeStmtGenerator) generateFlattenedCTE() string {
 		}
 		flattenedProjs = append(flattenedProjs, castStmt)
 	}
-	flattenedProjs = append(flattenedProjs, "_peerdb_timestamp")
-	flattenedProjs = append(flattenedProjs, "_peerdb_timestamp_nanos")
-	flattenedProjs = append(flattenedProjs, "_peerdb_record_type")
-	flattenedProjs = append(flattenedProjs, "_peerdb_unchanged_toast_columns")
+	flattenedProjs = append(
+		flattenedProjs,
+		"_peerdb_timestamp",
+		"_peerdb_timestamp_nanos",
+		"_peerdb_record_type",
+		"_peerdb_unchanged_toast_columns",
+	)
 
 	// normalize anything between last normalized batch id to last sync batchid
 	return fmt.Sprintf(`WITH _peerdb_flattened AS
@@ -126,8 +129,8 @@ func (m *mergeStmtGenerator) generateDeDupedCTE() string {
 // generateMergeStmt generates a merge statement.
 func (m *mergeStmtGenerator) generateMergeStmt(tempTable string) string {
 	// comma separated list of column names
-	backtickColNames := make([]string, 0)
-	pureColNames := make([]string, 0)
+	backtickColNames := make([]string, 0, len(m.NormalizedTableSchema.Columns))
+	pureColNames := make([]string, 0, len(m.NormalizedTableSchema.Columns))
 	for colName := range m.NormalizedTableSchema.Columns {
 		backtickColNames = append(backtickColNames, fmt.Sprintf("`%s`", colName))
 		pureColNames = append(pureColNames, colName)

flow/connectors/snowflake/qrep.go

@@ -15,6 +15,7 @@ import (
 	"github.com/aws/aws-sdk-go/service/s3"
 	"github.com/aws/aws-sdk-go/service/s3/s3manager"
 	"github.com/jackc/pgx/v5/pgtype"
+	"golang.org/x/exp/maps"
 	"google.golang.org/protobuf/encoding/protojson"
 )
 
@@ -308,14 +309,10 @@ func (c *SnowflakeConnector) getColsFromTable(tableName string) (*model.ColumnIn
 		}
 		columnMap[colName.String] = colType.String
 	}
-	var cols []string
-	for k := range columnMap {
-		cols = append(cols, k)
-	}
 
 	return &model.ColumnInformation{
 		ColumnMap: columnMap,
-		Columns:   cols,
+		Columns:   maps.Keys(columnMap),
 	}, nil
 }
 

flow/connectors/utils/array.go

@@ -1,7 +1,7 @@
 package utils
 
 func ArrayMinus(first []string, second []string) []string {
-	lookup := make(map[string]struct{})
+	lookup := make(map[string]struct{}, len(second))
 	// Add elements from arrayB to the lookup map
 	for _, element := range second {
 		lookup[element] = struct{}{}

flow/connectors/utils/map.go

@@ -1,15 +1,15 @@
 package utils
 
-import "strings"
+import (
+	"strings"
+
+	"golang.org/x/exp/maps"
+)
 
 func KeysToString(m map[string]struct{}) string {
 	if m == nil {
 		return ""
 	}
 
-	var keys []string
-	for k := range m {
-		keys = append(keys, k)
-	}
-	return strings.Join(keys, ",")
+	return strings.Join(maps.Keys(m), ",")
 }

flow/e2e/test_utils.go

@@ -183,7 +183,7 @@ func CreateSourceTableQRep(pool *pgxpool.Pool, suffix string, tableName string)
 }
 
 func generate20MBJson() ([]byte, error) {
-	xn := make(map[string]interface{})
+	xn := make(map[string]interface{}, 215000)
 	for i := 0; i < 215000; i++ {
 		xn[uuid.New().String()] = uuid.New().String()
 	}

flow/model/model.go

@@ -132,7 +132,7 @@ func (r *RecordItems) toMap() (map[string]interface{}, error) {
 		return nil, errors.New("colToValIdx is nil")
 	}
 
-	jsonStruct := make(map[string]interface{})
+	jsonStruct := make(map[string]interface{}, len(r.ColToValIdx))
 	for col, idx := range r.ColToValIdx {
 		v := r.Values[idx]
 		if v.Value == nil {
@@ -178,7 +178,7 @@ type ToJSONOptions struct {
 }
 
 func NewToJSONOptions(unnestCols []string) *ToJSONOptions {
-	unnestColumns := make(map[string]struct{})
+	unnestColumns := make(map[string]struct{}, len(unnestCols))
 	for _, col := range unnestCols {
 		unnestColumns[col] = struct{}{}
 	}