planner: make converge index merge path feel the prefer tiflash hint (#56227)

close #56217

Author: AilinKid

pkg/executor/test/tiflashtest/BUILD.bazel

@@ -9,7 +9,7 @@ go_test(
     ],
     flaky = True,
     race = "on",
-    shard_count = 44,
+    shard_count = 45,
     deps = [
         "//pkg/config",
         "//pkg/domain",

pkg/executor/test/tiflashtest/tiflash_test.go

@@ -2117,3 +2117,35 @@ func TestMppTableReaderCacheForSingleSQL(t *testing.T) {
 		require.Equal(t, tc.expectMissNum, missNum.Load())
 	}
 }
+
+func TestIndexMergeCarePreferTiflash(t *testing.T) {
+	store := testkit.CreateMockStore(t, withMockTiFlash(1))
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("CREATE TABLE `t` (" +
+		"`i` bigint(20) NOT NULL, " +
+		"`w` varchar(32) NOT NULL," +
+		"`l` varchar(32) NOT NULL," +
+		"`a` tinyint(4) NOT NULL DEFAULT '0'," +
+		"`m` int(11) NOT NULL DEFAULT '0'," +
+		"`s` int(11) NOT NULL DEFAULT '0'," +
+		"PRIMARY KEY (`i`) /*T![clustered_index] NONCLUSTERED */," +
+		"KEY `idx_win_user_site_code` (`w`,`m`)," +
+		"KEY `idx_lose_user_site_code` (`l`,`m`)," +
+		"KEY `idx_win_site_code_status` (`w`,`a`)," +
+		"KEY `idx_lose_site_code_status` (`l`,`a`)" +
+		")")
+	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.MustQuery("explain format=\"brief\" SELECT" +
+		"      /*+ read_from_storage(tiflash[a]) */ a.i FROM t a WHERE a.s = 0 AND a.a NOT IN (-1, 0) AND m >= 1726910326 AND m <= 1726910391 AND ( a.w IN ('1123') OR a.l IN ('1123'))").Check(
+		testkit.Rows("TableReader 0.00 root  MppVersion: 2, data:ExchangeSender",
+			"└─ExchangeSender 0.00 mpp[tiflash]  ExchangeType: PassThrough",
+			"  └─Projection 0.00 mpp[tiflash]  test.t.i",
+			"    └─Selection 0.00 mpp[tiflash]  ge(test.t.m, 1726910326), le(test.t.m, 1726910391), not(in(test.t.a, -1, 0)), or(eq(test.t.w, \"1123\"), eq(test.t.l, \"1123\"))",
+			"      └─TableFullScan 10.00 mpp[tiflash] table:a pushed down filter:eq(test.t.s, 0), keep order:false, stats:pseudo"))
+}

pkg/planner/core/casetest/physicalplantest/testdata/plan_suite_out.json

@@ -406,11 +406,11 @@
           "└─ExchangeSender 4439.11 mpp[tiflash]  ExchangeType: PassThrough",
           "  └─Projection 4439.11 mpp[tiflash]  test.t.a, Column#5",
           "    └─Projection 4439.11 mpp[tiflash]  Column#5, test.t.a",
-          "      └─HashAgg 4439.11 mpp[tiflash]  group by:test.t.a, test.t.c, funcs:sum(Column#14)->Column#5, funcs:firstrow(test.t.a)->test.t.a",
+          "      └─HashAgg 4439.11 mpp[tiflash]  group by:test.t.a, test.t.c, funcs:sum(Column#8)->Column#5, funcs:firstrow(test.t.a)->test.t.a",
           "        └─ExchangeReceiver 4439.11 mpp[tiflash]  ",
           "          └─ExchangeSender 4439.11 mpp[tiflash]  ExchangeType: HashPartition, Compression: FAST, Hash Cols: [name: test.t.a, collate: binary], [name: test.t.c, collate: binary]",
-          "            └─HashAgg 4439.11 mpp[tiflash]  group by:Column#17, Column#18, funcs:sum(Column#16)->Column#14",
-          "              └─Projection 5548.89 mpp[tiflash]  cast(test.t.b, decimal(10,0) BINARY)->Column#16, test.t.a->Column#17, test.t.c->Column#18",
+          "            └─HashAgg 4439.11 mpp[tiflash]  group by:Column#11, Column#12, funcs:sum(Column#10)->Column#8",
+          "              └─Projection 5548.89 mpp[tiflash]  cast(test.t.b, decimal(10,0) BINARY)->Column#10, test.t.a->Column#11, test.t.c->Column#12",
           "                └─Selection 5548.89 mpp[tiflash]  or(lt(test.t.b, 2), gt(test.t.a, 2))",
           "                  └─TableFullScan 10000.00 mpp[tiflash] table:t pushed down filter:empty, keep order:false, stats:pseudo"
         ],

pkg/planner/core/find_best_task.go

@@ -1377,6 +1377,10 @@ func findBestTask4DS(ds *DataSource, prop *property.PhysicalProperty, planCounte
 	for _, candidate := range candidates {
 		path := candidate.path
 		if path.PartialIndexPaths != nil {
+			// prefer tiflash, while current table path is tikv, skip it.
+			if ds.PreferStoreType&h.PreferTiFlash != 0 && path.StoreType == kv.TiKV {
+				continue
+			}
 			idxMergeTask, err := convertToIndexMergeScan(ds, prop, candidate, opt)
 			if err != nil {
 				return nil, 0, err
@@ -1512,9 +1516,11 @@ func findBestTask4DS(ds *DataSource, prop *property.PhysicalProperty, planCounte
 			}
 		}
 		if path.IsTablePath() {
+			// prefer tiflash, while current table path is tikv, skip it.
 			if ds.PreferStoreType&h.PreferTiFlash != 0 && path.StoreType == kv.TiKV {
 				continue
 			}
+			// prefer tikv, while current table path is tiflash, skip it.
 			if ds.PreferStoreType&h.PreferTiKV != 0 && path.StoreType == kv.TiFlash {
 				continue
 			}