planner: fix tiflash path will be identified as table dual (#49338)

close #49285

pkg/planner/core/casetest/enforcempp/enforce_mpp_test.go

@@ -41,6 +41,7 @@ func TestEnforceMPP(t *testing.T) {
 	tk.MustExec("create table t(a int, b int)")
 	tk.MustExec("create index idx on t(a)")
 	tk.MustExec("CREATE TABLE `s` (\n  `a` int(11) DEFAULT NULL,\n  `b` int(11) DEFAULT NULL,\n  `c` int(11) DEFAULT NULL,\n  `d` int(11) DEFAULT NULL,\n  UNIQUE KEY `a` (`a`),\n  KEY `ii` (`a`,`b`)\n)")
+	tk.MustExec("create table t3(id int, sala char(10), name char(100), primary key(id, sala)) partition by list columns (sala)(partition p1 values in('a'));")
 
 	// Default RPC encoding may cause statistics explain result differ and then the test unstable.
 	tk.MustExec("set @@tidb_enable_chunk_rpc = on")
@@ -65,6 +66,12 @@ func TestEnforceMPP(t *testing.T) {
 				Available: true,
 			}
 		}
+		if tblInfo.Name.L == "t3" {
+			tblInfo.TiFlashReplica = &model.TiFlashReplicaInfo{
+				Count:     1,
+				Available: true,
+			}
+		}
 	}
 
 	var input []string

pkg/planner/core/casetest/enforcempp/testdata/enforce_mpp_suite_in.json

@@ -22,7 +22,9 @@
       "explain format='verbose' select count(*) from t where a=1",
       "explain format='verbose' select /*+ read_from_storage(tikv[t]) */ count(*) from t where a=1",
       "explain format='verbose' select /*+ read_from_storage(tiflash[t]) */ count(*) from t where a=1",
-      "explain select  /*+ READ_FROM_STORAGE(TIFLASH[s]) */ a from s where a = 10 and b is null; -- index path huristic rule will prune tiflash path"
+      "explain select  /*+ READ_FROM_STORAGE(TIFLASH[s]) */ a from s where a = 10 and b is null; -- index path huristic rule will prune tiflash path",
+      "explain select /*+ read_from_storage(tiflash[t3]) */ * from t3 where sala='a' and id =1; -- once hinted, walk with tiflash range scan",
+      "explain select * from t3 where sala='a' and id =1; -- once not hinted, walk with tikv point get"
     ]
   },
   {

pkg/planner/core/casetest/enforcempp/testdata/enforce_mpp_suite_out.json

@@ -177,13 +177,33 @@
       {
         "SQL": "explain select  /*+ READ_FROM_STORAGE(TIFLASH[s]) */ a from s where a = 10 and b is null; -- index path huristic rule will prune tiflash path",
         "Plan": [
-          "TableReader_12 0.10 root  MppVersion: 2, data:ExchangeSender_11",
-          "└─ExchangeSender_11 0.10 mpp[tiflash]  ExchangeType: PassThrough",
+          "TableReader_9 0.10 root  MppVersion: 2, data:ExchangeSender_8",
+          "└─ExchangeSender_8 0.10 mpp[tiflash]  ExchangeType: PassThrough",
           "  └─Projection_5 0.10 mpp[tiflash]  test.s.a",
-          "    └─Selection_10 0.10 mpp[tiflash]  isnull(test.s.b)",
-          "      └─TableFullScan_9 10.00 mpp[tiflash] table:s pushed down filter:eq(test.s.a, 10), keep order:false, stats:pseudo"
+          "    └─Selection_7 0.10 mpp[tiflash]  isnull(test.s.b)",
+          "      └─TableFullScan_6 10.00 mpp[tiflash] table:s pushed down filter:eq(test.s.a, 10), keep order:false, stats:pseudo"
         ],
         "Warn": null
+      },
+      {
+        "SQL": "explain select /*+ read_from_storage(tiflash[t3]) */ * from t3 where sala='a' and id =1; -- once hinted, walk with tiflash range scan",
+        "Plan": [
+          "TableReader_12 0.01 root  MppVersion: 2, data:ExchangeSender_11",
+          "└─ExchangeSender_11 0.01 mpp[tiflash]  ExchangeType: PassThrough",
+          "  └─TableRangeScan_10 1.00 mpp[tiflash] table:t3, partition:p1 range:[1 \"a\",1 \"a\"], keep order:false, stats:pseudo"
+        ],
+        "Warn": [
+          "disable dynamic pruning due to t3 has no global stats"
+        ]
+      },
+      {
+        "SQL": "explain select * from t3 where sala='a' and id =1; -- once not hinted, walk with tikv point get",
+        "Plan": [
+          "Point_Get_6 1.00 root table:t3, partition:p1, clustered index:PRIMARY(id, sala) "
+        ],
+        "Warn": [
+          "disable dynamic pruning due to t3 has no global stats"
+        ]
       }
     ]
   },

pkg/planner/core/stats.go

@@ -307,6 +307,22 @@ func (ds *DataSource) derivePathStatsAndTryHeuristics() error {
 		selected, uniqueBest, refinedBest *util.AccessPath
 		isRefinedPath                     bool
 	)
+	// step1: if user prefer tiFlash store type, tiFlash path should always be built anyway ahead.
+	var tiflashPath *util.AccessPath
+	if ds.preferStoreType&preferTiFlash != 0 {
+		for _, path := range ds.possibleAccessPaths {
+			if path.StoreType == kv.TiFlash {
+				err := ds.deriveTablePathStats(path, ds.pushedDownConds, false)
+				if err != nil {
+					return err
+				}
+				path.IsSingleScan = true
+				tiflashPath = path
+				break
+			}
+		}
+	}
+	// step2: kv path should follow the heuristic rules.
 	for _, path := range ds.possibleAccessPaths {
 		if path.IsTablePath() {
 			err := ds.deriveTablePathStats(path, ds.pushedDownConds, false)
@@ -318,7 +334,9 @@ func (ds *DataSource) derivePathStatsAndTryHeuristics() error {
 			ds.deriveIndexPathStats(path, ds.pushedDownConds, false)
 			path.IsSingleScan = ds.isSingleScan(path.FullIdxCols, path.FullIdxColLens)
 		}
+		// step: 3
 		// Try some heuristic rules to select access path.
+		// tiFlash path also have table-range-scan (range point like here) to be heuristic treated.
 		if len(path.Ranges) == 0 {
 			selected = path
 			break
@@ -381,13 +399,15 @@ func (ds *DataSource) derivePathStatsAndTryHeuristics() error {
 	// heuristic rule pruning other path should consider hint prefer.
 	// If no hints and some path matches a heuristic rule, just remove other possible paths.
 	if selected != nil {
-		// if user wanna tiFlash read, while current heuristic choose a TiKV path. so we shouldn't prune other paths.
+		ds.possibleAccessPaths[0] = selected
+		ds.possibleAccessPaths = ds.possibleAccessPaths[:1]
+		// if user wanna tiFlash read, while current heuristic choose a TiKV path. so we shouldn't prune tiFlash path.
 		keep := ds.preferStoreType&preferTiFlash != 0 && selected.StoreType != kv.TiFlash
 		if keep {
+			// also keep tiflash path as well.
+			ds.possibleAccessPaths = append(ds.possibleAccessPaths, tiflashPath)
 			return nil
 		}
-		ds.possibleAccessPaths[0] = selected
-		ds.possibleAccessPaths = ds.possibleAccessPaths[:1]
 		var tableName string
 		if ds.TableAsName.O == "" {
 			tableName = ds.tableInfo.Name.O