cherry pick pingcap#19754 to release-4.0

Signed-off-by: ti-srebot <ti-srebot@pingcap.com>
ti-srebot · Sep 3, 2020 · 809e69c · 809e69c
1 parent 104d372
commit 809e69c
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Showing 2 changed files with 3 additions and 1 deletion.
diff --git a/expression/builtin_compare_vec.go b/expression/builtin_compare_vec.go
@@ -254,6 +254,7 @@ func (b *builtinLeastStringSig) vecEvalString(input *chunk.Chunk, result *chunk.
 	src := result
 	arg := buf1
 	dst := buf2
+	dst.ReserveString(n)
 	for j := 1; j < len(b.args); j++ {
 		if err := b.args[j].VecEvalString(b.ctx, input, arg); err != nil {
 			return err
@@ -793,6 +794,7 @@ func (b *builtinGreatestStringSig) vecEvalString(input *chunk.Chunk, result *chu
 	src := result
 	arg := buf1
 	dst := buf2
+	dst.ReserveString(n)
 	for j := 1; j < len(b.args); j++ {
 		if err := b.args[j].VecEvalString(b.ctx, input, arg); err != nil {
 			return err

diff --git a/util/chunk/column.go b/util/chunk/column.go
@@ -703,7 +703,7 @@ func (c *Column) MergeNulls(cols ...*Column) {
 	}
 	for _, col := range cols {
 		if c.length != col.length {
-			panic("should ensure all columns have the same length")
+			panic(fmt.Sprintf("should ensure all columns have the same length, expect %v, but got %v", c.length, col.length))
 		}
 	}
 	for _, col := range cols {