planner: fix index heuristic rule will prune out hint preferred tiflash path

planner/core/casetest/enforcempp/enforce_mpp_test.go

@@ -39,6 +39,7 @@ func TestEnforceMPP(t *testing.T) {
  tk.MustExec("drop table if exists 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)")
 
  // Default RPC encoding may cause statistics explain result differ and then the test unstable.
  tk.MustExec("set @@tidb_enable_chunk_rpc = on")
@@ -57,6 +58,12 @@ func TestEnforceMPP(t *testing.T) {
  Available: true,
  }
  }
+ if tblInfo.Name.L == "s" {
+ tblInfo.TiFlashReplica = &model.TiFlashReplicaInfo{
+ Count: 1,
+ Available: true,
+ }
+ }
  }
 
  var input []string

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

@@ -21,7 +21,8 @@
  "set @@tidb_enforce_mpp=1;",
  "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 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"
  ]
  },
  {

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

@@ -173,6 +173,17 @@
  " └─TableFullScan_25 10000.00 928000.00 batchCop[tiflash] table:t pushed down filter:empty, keep order:false, stats:pseudo"
  ],
  "Warn": null
+ },
+ {
+ "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",
+ " └─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"
+ ],
+ "Warn": null
  }
  ]
  },

planner/core/stats.go

@@ -24,6 +24,7 @@
  "github.com/pingcap/errors"
  "github.com/pingcap/tidb/domain"
  "github.com/pingcap/tidb/expression"
+ "github.com/pingcap/tidb/kv"
  "github.com/pingcap/tidb/parser/model"
  "github.com/pingcap/tidb/parser/mysql"
  "github.com/pingcap/tidb/planner/property"
@@ -415,8 +416,14 @@
  selected = uniqueBest
  }
  }
- // If some path matches a heuristic rule, just remove other possible paths
+ // 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.
+ keep := ds.preferStoreType&preferTiFlash != 0 && selected.StoreType != kv.TiFlash
+ if keep {
+ return nil
+ }
  ds.possibleAccessPaths[0] = selected
  ds.possibleAccessPaths = ds.possibleAccessPaths[:1]
  var tableName string