skip metadata for queries which are not cas

conn.go

@@ -662,10 +662,15 @@ func (c *Conn) executeQuery(qry *Query) *Iter {
 		params.pageSize = qry.pageSize
 	}
 
-	var frame frameWriter
+	var (
+		frame frameWriter
+		info  *QueryInfo
+	)
+
 	if qry.shouldPrepare() {
 		// Prepare all DML queries. Other queries can not be prepared.
-		info, err := c.prepareStatement(qry.stmt, qry.trace)
+		var err error
+		info, err = c.prepareStatement(qry.stmt, qry.trace)
 		if err != nil {
 			return &Iter{err: err}
 		}
@@ -697,6 +702,8 @@ func (c *Conn) executeQuery(qry *Query) *Iter {
 			// TODO: handle query binding names
 		}
 
+		params.skipMeta = !qry.isCAS
+
 		frame = &writeExecuteFrame{
 			preparedID: info.Id,
 			params:     params,
@@ -732,6 +739,14 @@ func (c *Conn) executeQuery(qry *Query) *Iter {
 			framer: framer,
 		}
 
+		if params.skipMeta {
+			if info != nil {
+				iter.meta.columns = info.Rval
+			} else {
+				return &Iter{framer: framer, err: errors.New("gocql: did not receive metadata but prepared info is nil")}
+			}
+		}
+
 		if len(x.meta.pagingState) > 0 && !qry.disableAutoPage {
 			iter.next = &nextIter{
 				qry: *qry,

frame.go

@@ -824,7 +824,8 @@ type resultMetadata struct {
 	// only if flagPageState
 	pagingState []byte
 
-	columns []ColumnInfo
+	columns  []ColumnInfo
+	colCount int
 
 	// this is a count of the total number of columns which can be scanned,
 	// it is at minimum len(columns) but may be larger, for instance when a column
@@ -856,15 +857,13 @@ func (f *framer) readCol(col *ColumnInfo, meta *resultMetadata, globalSpec bool,
 }
 
 func (f *framer) parseResultMetadata() resultMetadata {
-	meta := resultMetadata{
-		flags: f.readInt(),
+	var meta resultMetadata
+	meta.flags = f.readInt()
+	meta.colCount = f.readInt()
+	if meta.colCount < 0 {
+		panic(fmt.Errorf("received negative column count: %d", meta.colCount))
 	}
-
-	colCount := f.readInt()
-	if colCount < 0 {
-		panic(fmt.Errorf("received negative column count: %d", colCount))
-	}
-	meta.actualColCount = colCount
+	meta.actualColCount = meta.colCount
 
 	if meta.flags&flagHasMorePages == flagHasMorePages {
 		meta.pagingState = f.readBytes()
@@ -882,17 +881,17 @@ func (f *framer) parseResultMetadata() resultMetadata {
 	}
 
 	var cols []ColumnInfo
-	if colCount < 1000 {
+	if meta.colCount < 1000 {
 		// preallocate columninfo to avoid excess copying
-		cols = make([]ColumnInfo, colCount)
-		for i := 0; i < colCount; i++ {
+		cols = make([]ColumnInfo, meta.colCount)
+		for i := 0; i < meta.colCount; i++ {
 			f.readCol(&cols[i], &meta, globalSpec, keyspace, table)
 		}
 
 	} else {
 		// use append, huge number of columns usually indicates a corrupt frame or
 		// just a huge row.
-		for i := 0; i < colCount; i++ {
+		for i := 0; i < meta.colCount; i++ {
 			var col ColumnInfo
 			f.readCol(&col, &meta, globalSpec, keyspace, table)
 			cols = append(cols, col)
@@ -950,7 +949,7 @@ func (f *framer) parseResultRows() frame {
 		panic(fmt.Errorf("invalid row_count in result frame: %d", numRows))
 	}
 
-	colCount := len(meta.columns)
+	colCount := meta.colCount
 
 	rows := make([][][]byte, numRows)
 	for i := 0; i < numRows; i++ {

session.go

@@ -576,6 +576,7 @@ type Query struct {
 	totalLatency     int64
 	serialCons       SerialConsistency
 	defaultTimestamp bool
+	isCAS            bool
 
 	disableAutoPage bool
 }
@@ -819,6 +820,7 @@ func (q *Query) Scan(dest ...interface{}) error {
 // the existing values did not match, the previous values will be stored
 // in dest.
 func (q *Query) ScanCAS(dest ...interface{}) (applied bool, err error) {
+	q.isCAS = true
 	iter := q.Iter()
 	if err := iter.checkErrAndNotFound(); err != nil {
 		return false, err
@@ -841,6 +843,7 @@ func (q *Query) ScanCAS(dest ...interface{}) (applied bool, err error) {
 // SELECT * FROM. So using ScanCAS with INSERT is inherently prone to
 // column mismatching. MapScanCAS is added to capture them safely.
 func (q *Query) MapScanCAS(dest map[string]interface{}) (applied bool, err error) {
+	q.isCAS = true
 	iter := q.Iter()
 	if err := iter.checkErrAndNotFound(); err != nil {
 		return false, err