vector: shorten explain output for vector constants

pkg/expression/constant.go

@@ -153,9 +153,9 @@ func (c *Constant) StringWithCtx(ctx ParamValues, redact string) string {
 		return c.DeferredExpr.StringWithCtx(ctx, redact)
 	}
 	if redact == perrors.RedactLogDisable {
-		return fmt.Sprintf("%v", c.Value.GetValue())
+		return fmt.Sprintf("%v", c.Value.StringTruncate())
 	} else if redact == perrors.RedactLogMarker {
-		return fmt.Sprintf("‹%v›", c.Value.GetValue())
+		return fmt.Sprintf("‹%v›", c.Value.StringTruncate())
 	}
 	return "?"
 }

pkg/expression/integration_test/BUILD.bazel

@@ -8,7 +8,7 @@ go_test(
         "main_test.go",
     ],
     flaky = True,
-    shard_count = 41,
+    shard_count = 42,
     deps = [
         "//pkg/config",
         "//pkg/domain",

pkg/expression/integration_test/integration_test.go

@@ -109,6 +109,31 @@ func TestVectorColumnInfo(t *testing.T) {
 	tk.MustGetErrMsg("create table t(embedding VECTOR(16384))", "vector cannot have more than 16383 dimensions")
 }
 
+func TestVectorConstantExplain(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec("CREATE TABLE t(c VECTOR);")
+	tk.MustExec("set session tidb_redact_log=off")
+	tk.MustQuery(`EXPLAIN SELECT VEC_COSINE_DISTANCE(c, '[1,2,3,4,5,6,7,8,9,10,11]') FROM t;`).Check(testkit.Rows(
+		"Projection_3 10000.00 root  vec_cosine_distance(test.t.c, [1,2,3,4,5,(6 more)...])->Column#3",
+		"└─TableReader_5 10000.00 root  data:TableFullScan_4",
+		"  └─TableFullScan_4 10000.00 cop[tikv] table:t keep order:false, stats:pseudo",
+	))
+	tk.MustExec("set session tidb_redact_log=on")
+	tk.MustQuery(`EXPLAIN SELECT VEC_COSINE_DISTANCE(c, VEC_FROM_TEXT('[1,2,3,4,5,6,7,8,9,10,11]')) FROM t;`).Check(testkit.Rows(
+		"Projection_3 10000.00 root  vec_cosine_distance(test.t.c, ?)->Column#3",
+		"└─TableReader_5 10000.00 root  data:TableFullScan_4",
+		"  └─TableFullScan_4 10000.00 cop[tikv] table:t keep order:false, stats:pseudo",
+	))
+	tk.MustExec("set session tidb_redact_log=marker")
+	tk.MustQuery(`EXPLAIN SELECT VEC_COSINE_DISTANCE(c, VEC_FROM_TEXT('[1,2,3,4,5,6,7,8,9,10,11]')) FROM t;`).Check(testkit.Rows(
+		"Projection_3 10000.00 root  vec_cosine_distance(test.t.c, ‹[1,2,3,4,5,(6 more)...]›)->Column#3",
+		"└─TableReader_5 10000.00 root  data:TableFullScan_4",
+		"  └─TableFullScan_4 10000.00 cop[tikv] table:t keep order:false, stats:pseudo",
+	))
+}
+
 func TestFixedVector(t *testing.T) {
 	store := testkit.CreateMockStore(t)
 	tk := testkit.NewTestKit(t, store)

pkg/types/datum.go

@@ -927,7 +927,7 @@ func (d *Datum) compareMysqlTime(ctx Context, time Time) (int, error) {
 	}
 }
 
-func (d *Datum) compareVectorFloat32(ctx Context, vec VectorFloat32) (int, error) {
+func (d *Datum) compareVectorFloat32(_ Context, vec VectorFloat32) (int, error) {
 	switch d.k {
 	case KindNull, KindMinNotNull:
 		return -1, nil
@@ -2082,6 +2082,16 @@ func (d *Datum) ToString() (string, error) {
 	}
 }
 
+// StringTruncate truncate long string.
+func (d *Datum) StringTruncate() string {
+	switch d.k {
+	case KindVectorFloat32:
+		return d.GetVectorFloat32().StringTruncate()
+	default:
+		return fmt.Sprintf("%v", d.GetValue())
+	}
+}
+
 // ToBytes gets the bytes representation of the datum.
 func (d *Datum) ToBytes() ([]byte, error) {
 	switch d.k {

pkg/types/vector.go

@@ -16,6 +16,7 @@ package types
 
 import (
 	"encoding/binary"
+	"fmt"
 	"math"
 	"strconv"
 	"unsafe"
@@ -93,7 +94,39 @@ func (v VectorFloat32) Elements() []float32 {
 	return unsafe.Slice((*float32)(unsafe.Pointer(&v.data[4])), l)
 }
 
-// String returns a string representation of the vector, which can be parsed later.
+// StringTruncate truncate vector to a readable format.
+func (v VectorFloat32) StringTruncate() string {
+	const (
+		maxDisplayElements = 5
+	)
+
+	truncatedElements := 0
+	elements := v.Elements()
+
+	if len(elements) > maxDisplayElements {
+		truncatedElements = len(elements) - maxDisplayElements
+		elements = elements[:maxDisplayElements]
+	}
+
+	buf := make([]byte, 0, 2+v.Len()*2)
+	buf = append(buf, '[')
+	for i, v := range elements {
+		if i > 0 {
+			buf = append(buf, ","...)
+		}
+		buf = strconv.AppendFloat(buf, float64(v), 'g', 2, 32)
+	}
+	if truncatedElements > 0 {
+		buf = append(buf, fmt.Sprintf(",(%d more)...", truncatedElements)...)
+	}
+	buf = append(buf, ']')
+
+	// buf is not used elsewhere, so it's safe to just cast to String
+	return unsafe.String(unsafe.SliceData(buf), len(buf))
+}
+
+// String implements the fmt.Stringer interface.
+// It returns a string representation of the vector which can be parsed later.
 func (v VectorFloat32) String() string {
 	elements := v.Elements()