use_index to support tiflash

Author: qw4990

pkg/executor/test/tiflashtest/BUILD.bazel

@@ -9,7 +9,7 @@ go_test(
     ],
     flaky = True,
     race = "on",
-    shard_count = 46,
+    shard_count = 47,
     deps = [
         "//pkg/config",
         "//pkg/domain",

pkg/executor/test/tiflashtest/tiflash_test.go

@@ -549,6 +549,23 @@ func TestPartitionTable(t *testing.T) {
 	failpoint.Disable("github.com/pingcap/tidb/pkg/executor/checkUseMPP")
 }
 
+func TestUseIndexTiFlash(t *testing.T) {
+	store := testkit.CreateMockStore(t, withMockTiFlash(2))
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec(`create table t (id int primary key, a int, b int, c int, key(a), key(b), key(c))`)
+	tk.MustExec(`alter table t set tiflash replica 1`)
+	tb := external.GetTableByName(t, tk, "test", "t")
+	err := domain.GetDomain(tk.Session()).DDLExecutor().UpdateTableReplicaInfo(tk.Session(), tb.Meta().ID, true)
+	require.NoError(t, err)
+
+	tk.MustUseIndex(`select /*+ use_index(t, a, b, c, tiflash) */ 1 from t where a=1`, "a")
+	tk.MustUseIndex(`select /*+ use_index(t, a, b, c, tiflash) */ 1 from t where b=1`, "b")
+	tk.MustUseIndex(`select /*+ use_index(t, a, b, c, tiflash) */ 1 from t where b=1`, "b")
+	plan := tk.MustQuery(`explain select /*+ use_index(t, a, b, c, tiflash) */ 1 from t`).Rows()
+	require.Equal(t, plan[len(plan)-1][2], "mpp[tiflash]")
+}
+
 func TestMppEnum(t *testing.T) {
 	store := testkit.CreateMockStore(t, withMockTiFlash(2))
 	tk := testkit.NewTestKit(t, store)

pkg/planner/core/planbuilder.go

@@ -1083,6 +1083,12 @@ func getPathByIndexName(paths []*util.AccessPath, idxName pmodel.CIStr, tblInfo
 		if path.IsTiKVTablePath() && isPrimaryIndex(idxName) && tblInfo.HasClusteredIndex() {
 			return path
 		}
+		if path.StoreType == kv.TiFlash && idxName.L == "tiflash" {
+			return path
+		}
+		if path.StoreType == kv.TiFlash {
+			continue
+		}
 		// If it's not a tikv table path and the index is nil, it could not be any index path.
 		if path.Index == nil {
 			continue