planner: fix partial index wrongly kept due to shared Range pointer mutation

pkg/util/ranger/ranger.go

@@ -653,6 +653,8 @@ type sortRange struct {
 // For two intervals [a, b], [c, d], we have guaranteed that a <= c. If b >= c. Then two intervals are overlapped.
 // And this two can be merged as [a, max(b, d)].
 // Otherwise they aren't overlapped.
+//
+// The function does not modify the caller's ranges (see issue #69779).
 func UnionRanges(sctx *rangerctx.RangerContext, ranges Ranges, mergeConsecutive bool) (Ranges, error) {
 	if len(ranges) == 0 {
 		return nil, nil
@@ -682,9 +684,14 @@ func UnionRanges(sctx *rangerctx.RangerContext, ranges Ranges, mergeConsecutive
 	})
 	ranges = ranges[:0]
 	lastRange := objects[0]
+	detached := false
 	for i := 1; i < len(objects); i++ {
 		if (mergeConsecutive && bytes.Compare(lastRange.encodedEnd, objects[i].encodedStart) >= 0) ||
 			(!mergeConsecutive && bytes.Compare(lastRange.encodedEnd, objects[i].encodedStart) > 0) {
+			if !detached {
+				lastRange.originalValue = lastRange.originalValue.Clone()
+				detached = true
+			}
 			if bytes.Compare(lastRange.encodedEnd, objects[i].encodedEnd) < 0 {
 				lastRange.encodedEnd = objects[i].encodedEnd
 				lastRange.originalValue.HighVal = objects[i].originalValue.HighVal
@@ -693,6 +700,7 @@ func UnionRanges(sctx *rangerctx.RangerContext, ranges Ranges, mergeConsecutive
 		} else {
 			ranges = append(ranges, lastRange.originalValue)
 			lastRange = objects[i]
+			detached = false
 		}
 	}
 	ranges = append(ranges, lastRange.originalValue)

pkg/util/ranger/ranger_test.go

@@ -2633,6 +2633,82 @@ func TestMinAccessCondsForDNFCond(t *testing.T) {
 	}
 }
 
+func TestUnionRangesPreservesCallerRanges(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	sctx := tk.Session()
+	rctx := sctx.GetRangerCtx()
+
+	// Build 3 ranges where r1 and r2 overlap so they trigger the merge path.
+	// r1 = [1, 3], r2 = [2, 4], r3 = [5, 7].
+	binaryCollator := collate.GetBinaryCollator()
+	r1 := &ranger.Range{
+		LowVal:      []types.Datum{types.NewIntDatum(1)},
+		HighVal:     []types.Datum{types.NewIntDatum(3)},
+		LowExclude:  false,
+		HighExclude: false,
+		Collators:   []collate.Collator{binaryCollator},
+	}
+	r2 := &ranger.Range{
+		LowVal:      []types.Datum{types.NewIntDatum(2)},
+		HighVal:     []types.Datum{types.NewIntDatum(4)},
+		LowExclude:  false,
+		HighExclude: false,
+		Collators:   []collate.Collator{binaryCollator},
+	}
+	r3 := &ranger.Range{
+		LowVal:      []types.Datum{types.NewIntDatum(5)},
+		HighVal:     []types.Datum{types.NewIntDatum(7)},
+		LowExclude:  false,
+		HighExclude: false,
+		Collators:   []collate.Collator{binaryCollator},
+	}
+	input := ranger.Ranges{r1, r2, r3}
+
+	// r1 and r2 overlap -> merged to [1, 4]. r3 is disjoint -> kept as [5, 7].
+	// Expected result: [[1, 4], [5, 7]].
+	result, err := ranger.UnionRanges(rctx, input, false /* mergeConsecutive */)
+	require.NoError(t, err)
+	require.Equal(t, 2, len(result))
+	require.Equal(t, int64(1), result[0].LowVal[0].GetInt64())
+	require.Equal(t, int64(4), result[0].HighVal[0].GetInt64())
+	require.Equal(t, int64(5), result[1].LowVal[0].GetInt64())
+	require.Equal(t, int64(7), result[1].HighVal[0].GetInt64())
+
+	// The original range objects must not be modified.
+	require.Equal(t, int64(1), r1.LowVal[0].GetInt64())
+	require.Equal(t, int64(3), r1.HighVal[0].GetInt64())
+	require.False(t, r1.HighExclude)
+	require.Equal(t, int64(2), r2.LowVal[0].GetInt64())
+	require.Equal(t, int64(4), r2.HighVal[0].GetInt64())
+	require.False(t, r2.HighExclude)
+	require.Equal(t, int64(5), r3.LowVal[0].GetInt64())
+	require.Equal(t, int64(7), r3.HighVal[0].GetInt64())
+	require.False(t, r3.HighExclude)
+
+	// [1, 4] and [5, 7] are consecutive after encoding (PrefixNext makes
+	// the encoded end of [1, 4] touch the encoded start of [5, 7]),
+	// so all three ranges merge into one: [1, 7].
+	input = ranger.Ranges{r1, r2, r3}
+	result2, err := ranger.UnionRanges(rctx, input, true /* mergeConsecutive */)
+	require.NoError(t, err)
+	require.Equal(t, 1, len(result2))
+	require.Equal(t, int64(1), result2[0].LowVal[0].GetInt64())
+	require.Equal(t, int64(7), result2[0].HighVal[0].GetInt64())
+
+	// The original range objects still must not be modified.
+	require.Equal(t, int64(1), r1.LowVal[0].GetInt64())
+	require.Equal(t, int64(3), r1.HighVal[0].GetInt64())
+	require.False(t, r1.HighExclude)
+	require.Equal(t, int64(2), r2.LowVal[0].GetInt64())
+	require.Equal(t, int64(4), r2.HighVal[0].GetInt64())
+	require.False(t, r2.HighExclude)
+	require.Equal(t, int64(5), r3.LowVal[0].GetInt64())
+	require.Equal(t, int64(7), r3.HighVal[0].GetInt64())
+	require.False(t, r3.HighExclude)
+}
+
 func TestBinCollationRangeForIndex(t *testing.T) {
 	store, dom := testkit.CreateMockStoreAndDomain(t)
 	tk := testkit.NewTestKit(t, store)

tests/integrationtest/r/planner/core/casetest/index/partialindex.result

@@ -107,4 +107,27 @@ IndexMerge	5555.56	root		type: union
 ├─IndexRangeScan(Build)	3333.33	cop[tikv]	table:tt, index:idx1(a)	range:(10,+inf], keep order:false, stats:pseudo
 ├─IndexRangeScan(Build)	3333.33	cop[tikv]	table:tt, index:idx2(b)	range:(10,+inf], keep order:false, stats:pseudo
 └─TableRowIDScan(Probe)	5555.56	cop[tikv]	table:tt	keep order:false, stats:pseudo
+drop table if exists t3;
+create table t3(id int primary key, a int not null, b int not null, index pi(b) where a < 3);
+insert into t3 values (1, 0, 1), (2, 1, 2), (3, 2, 3), (4, 3, 4), (5, 10, 5);
+explain format='brief' select * from t3 where a >= 0;
+id	estRows	task	access object	operator info
+TableReader	3333.33	root		data:Selection
+└─Selection	3333.33	cop[tikv]		ge(planner__core__casetest__index__partialindex.t3.a, 0)
+  └─TableFullScan	10000.00	cop[tikv]	table:t3	keep order:false, stats:pseudo
+select id, a, b from t3 where a >= 0 order by b limit 5;
+id	a	b
+1	0	1
+2	1	2
+3	2	3
+4	3	4
+5	10	5
+select id, a, b from t3 ignore index(pi) where a >= 0 order by b limit 5;
+id	a	b
+1	0	1
+2	1	2
+3	2	3
+4	3	4
+5	10	5
+drop table t3;
 drop table t, tt;

tests/integrationtest/t/planner/core/casetest/index/partialindex.test

@@ -36,4 +36,14 @@ explain format='brief' select /*+ inl_join(t2) */ * from tt t1, tt t2 where t1.b
 explain format='brief' select /*+ use_index_merge(t, idx1, idx2) */ * from t where (a > 10) or (b > 10);
 explain format='brief' select /*+ use_index_merge(tt, idx1, idx2) */ * from tt where (a > 10) or (b > 10);
 
+# TestPartialIndexImplicationCheck
+# a >= 0 does NOT imply a < 3, partial index pi should NOT be used.
+drop table if exists t3;
+create table t3(id int primary key, a int not null, b int not null, index pi(b) where a < 3);
+insert into t3 values (1, 0, 1), (2, 1, 2), (3, 2, 3), (4, 3, 4), (5, 10, 5);
+explain format='brief' select * from t3 where a >= 0;
+select id, a, b from t3 where a >= 0 order by b limit 5;
+select id, a, b from t3 ignore index(pi) where a >= 0 order by b limit 5;
+drop table t3;
+
 drop table t, tt;