planner: variable tidb_opt_enable_hash_join to skip hash join (#46575)

close #46695
pingcap · Sep 26, 2023 · 95fa30c · 95fa30c
1 parent ee719a4
commit 95fa30c
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Showing 8 changed files with 192 additions and 8 deletions.
diff --git a/planner/core/casetest/rule/BUILD.bazel b/planner/core/casetest/rule/BUILD.bazel
@@ -12,7 +12,7 @@ go_test(
     ],
     data = glob(["testdata/**"]),
     flaky = True,
-    shard_count = 23,
+    shard_count = 24,
     deps = [
         "//domain",
         "//expression",

diff --git a/planner/core/casetest/rule/rule_join_reorder_test.go b/planner/core/casetest/rule/rule_join_reorder_test.go
@@ -72,6 +72,19 @@ func TestNoHashJoinHint(t *testing.T) {
 	runJoinReorderTestData(t, tk, "TestNoHashJoinHint")
 }
 
+// test the global/session variable tidb_opt_enable_hash_join being set to no
+func TestOptEnableHashJoin(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec("set tidb_opt_enable_hash_join=off")
+	tk.MustExec("create table t1(a int, b int, key(a));")
+	tk.MustExec("create table t2(a int, b int, key(a));")
+	tk.MustExec("create table t3(a int, b int, key(a));")
+	tk.MustExec("create table t4(a int, b int, key(a));")
+	runJoinReorderTestData(t, tk, "TestOptEnableHashJoin")
+}
+
 func TestNoMergeJoinHint(t *testing.T) {
 	store := testkit.CreateMockStore(t)
 	tk := testkit.NewTestKit(t, store)

diff --git a/planner/core/casetest/rule/testdata/join_reorder_suite_in.json b/planner/core/casetest/rule/testdata/join_reorder_suite_in.json
@@ -49,6 +49,21 @@
       "select /*+ leading(t1, t2, t3, t4), hash_join(t1, t2), no_hash_join(t3), hash_join(t4) */ * from t1, t2, t3, t4"
     ]
   },
+  {
+    "name": "TestOptEnableHashJoin",
+    "cases": [
+      "select * from t1, t2",
+      "select * from t1, t2 where t1.a=t2.a",
+      "select * from t1, t2 where t1.b=t2.b",
+      "select * from t1, t2 where t1.a=t2.a and t1.b=t2.b",
+      "select * from t1 left join t2 on t1.b=t2.b",
+      "select * from t1 left join t2 on t1.a=t2.a",
+      "select * from t1 right join t2 on t1.b=t2.b",
+      "select * from t1 right join t2 on t1.a=t2.a",
+      "select /*+ hash_join(t1) */ * from t1, t2",
+      "select /*+ hash_join(t2) */ * from t1, t2"
+    ]
+  },
   {
     "name": "TestNoIndexJoinHint",
     "cases": [

diff --git a/planner/core/casetest/rule/testdata/join_reorder_suite_out.json b/planner/core/casetest/rule/testdata/join_reorder_suite_out.json
@@ -609,7 +609,7 @@
           "  └─TableFullScan 10000.00 cop[tikv] table:t1 keep order:false, stats:pseudo"
         ],
         "Warning": [
-          "Warning 1815 Some HASH_JOIN and NO_HASH_JOIN hints conflict, NO_HASH_JOIN is ignored"
+          "Warning 1815 A conflict between the HASH_JOIN hint and the NO_HASH_JOIN hint, or the tidb_opt_enable_hash_join system variable, the HASH_JOIN hint will take precedence."
         ]
       },
       {
@@ -622,7 +622,7 @@
           "  └─TableFullScan 10000.00 cop[tikv] table:t1 keep order:false, stats:pseudo"
         ],
         "Warning": [
-          "Warning 1815 Some HASH_JOIN and NO_HASH_JOIN hints conflict, NO_HASH_JOIN is ignored"
+          "Warning 1815 A conflict between the HASH_JOIN hint and the NO_HASH_JOIN hint, or the tidb_opt_enable_hash_join system variable, the HASH_JOIN hint will take precedence."
         ]
       },
       {
@@ -782,6 +782,147 @@
       }
     ]
   },
+  {
+    "Name": "TestOptEnableHashJoin",
+    "Cases": [
+      {
+        "SQL": "select * from t1, t2",
+        "Plan": [
+          "MergeJoin 100000000.00 root  inner join",
+          "├─TableReader(Build) 10000.00 root  data:TableFullScan",
+          "│ └─TableFullScan 10000.00 cop[tikv] table:t2 keep order:false, stats:pseudo",
+          "└─TableReader(Probe) 10000.00 root  data:TableFullScan",
+          "  └─TableFullScan 10000.00 cop[tikv] table:t1 keep order:false, stats:pseudo"
+        ],
+        "Warning": null
+      },
+      {
+        "SQL": "select * from t1, t2 where t1.a=t2.a",
+        "Plan": [
+          "IndexHashJoin 12487.50 root  inner join, inner:IndexLookUp, outer key:test.t1.a, inner key:test.t2.a, equal cond:eq(test.t1.a, test.t2.a)",
+          "├─TableReader(Build) 9990.00 root  data:Selection",
+          "│ └─Selection 9990.00 cop[tikv]  not(isnull(test.t1.a))",
+          "│   └─TableFullScan 10000.00 cop[tikv] table:t1 keep order:false, stats:pseudo",
+          "└─IndexLookUp(Probe) 12487.50 root  ",
+          "  ├─Selection(Build) 12487.50 cop[tikv]  not(isnull(test.t2.a))",
+          "  │ └─IndexRangeScan 12500.00 cop[tikv] table:t2, index:a(a) range: decided by [eq(test.t2.a, test.t1.a)], keep order:false, stats:pseudo",
+          "  └─TableRowIDScan(Probe) 12487.50 cop[tikv] table:t2 keep order:false, stats:pseudo"
+        ],
+        "Warning": null
+      },
+      {
+        "SQL": "select * from t1, t2 where t1.b=t2.b",
+        "Plan": [
+          "MergeJoin 12487.50 root  inner join, left key:test.t1.b, right key:test.t2.b",
+          "├─Sort(Build) 9990.00 root  test.t2.b",
+          "│ └─TableReader 9990.00 root  data:Selection",
+          "│   └─Selection 9990.00 cop[tikv]  not(isnull(test.t2.b))",
+          "│     └─TableFullScan 10000.00 cop[tikv] table:t2 keep order:false, stats:pseudo",
+          "└─Sort(Probe) 9990.00 root  test.t1.b",
+          "  └─TableReader 9990.00 root  data:Selection",
+          "    └─Selection 9990.00 cop[tikv]  not(isnull(test.t1.b))",
+          "      └─TableFullScan 10000.00 cop[tikv] table:t1 keep order:false, stats:pseudo"
+        ],
+        "Warning": null
+      },
+      {
+        "SQL": "select * from t1, t2 where t1.a=t2.a and t1.b=t2.b",
+        "Plan": [
+          "IndexHashJoin 12475.01 root  inner join, inner:IndexLookUp, outer key:test.t1.a, inner key:test.t2.a, equal cond:eq(test.t1.a, test.t2.a), eq(test.t1.b, test.t2.b)",
+          "├─TableReader(Build) 9980.01 root  data:Selection",
+          "│ └─Selection 9980.01 cop[tikv]  not(isnull(test.t1.a)), not(isnull(test.t1.b))",
+          "│   └─TableFullScan 10000.00 cop[tikv] table:t1 keep order:false, stats:pseudo",
+          "└─IndexLookUp(Probe) 12475.01 root  ",
+          "  ├─Selection(Build) 12487.50 cop[tikv]  not(isnull(test.t2.a))",
+          "  │ └─IndexRangeScan 12500.00 cop[tikv] table:t2, index:a(a) range: decided by [eq(test.t2.a, test.t1.a)], keep order:false, stats:pseudo",
+          "  └─Selection(Probe) 12475.01 cop[tikv]  not(isnull(test.t2.b))",
+          "    └─TableRowIDScan 12487.50 cop[tikv] table:t2 keep order:false, stats:pseudo"
+        ],
+        "Warning": null
+      },
+      {
+        "SQL": "select * from t1 left join t2 on t1.b=t2.b",
+        "Plan": [
+          "MergeJoin 12487.50 root  left outer join, left key:test.t1.b, right key:test.t2.b",
+          "├─Sort(Build) 9990.00 root  test.t2.b",
+          "│ └─TableReader 9990.00 root  data:Selection",
+          "│   └─Selection 9990.00 cop[tikv]  not(isnull(test.t2.b))",
+          "│     └─TableFullScan 10000.00 cop[tikv] table:t2 keep order:false, stats:pseudo",
+          "└─Sort(Probe) 10000.00 root  test.t1.b",
+          "  └─TableReader 10000.00 root  data:TableFullScan",
+          "    └─TableFullScan 10000.00 cop[tikv] table:t1 keep order:false, stats:pseudo"
+        ],
+        "Warning": null
+      },
+      {
+        "SQL": "select * from t1 left join t2 on t1.a=t2.a",
+        "Plan": [
+          "IndexHashJoin 12487.50 root  left outer join, inner:IndexLookUp, outer key:test.t1.a, inner key:test.t2.a, equal cond:eq(test.t1.a, test.t2.a)",
+          "├─TableReader(Build) 10000.00 root  data:TableFullScan",
+          "│ └─TableFullScan 10000.00 cop[tikv] table:t1 keep order:false, stats:pseudo",
+          "└─IndexLookUp(Probe) 12487.50 root  ",
+          "  ├─Selection(Build) 12487.50 cop[tikv]  not(isnull(test.t2.a))",
+          "  │ └─IndexRangeScan 12500.00 cop[tikv] table:t2, index:a(a) range: decided by [eq(test.t2.a, test.t1.a)], keep order:false, stats:pseudo",
+          "  └─TableRowIDScan(Probe) 12487.50 cop[tikv] table:t2 keep order:false, stats:pseudo"
+        ],
+        "Warning": null
+      },
+      {
+        "SQL": "select * from t1 right join t2 on t1.b=t2.b",
+        "Plan": [
+          "MergeJoin 12487.50 root  right outer join, left key:test.t1.b, right key:test.t2.b",
+          "├─Sort(Build) 9990.00 root  test.t1.b",
+          "│ └─TableReader 9990.00 root  data:Selection",
+          "│   └─Selection 9990.00 cop[tikv]  not(isnull(test.t1.b))",
+          "│     └─TableFullScan 10000.00 cop[tikv] table:t1 keep order:false, stats:pseudo",
+          "└─Sort(Probe) 10000.00 root  test.t2.b",
+          "  └─TableReader 10000.00 root  data:TableFullScan",
+          "    └─TableFullScan 10000.00 cop[tikv] table:t2 keep order:false, stats:pseudo"
+        ],
+        "Warning": null
+      },
+      {
+        "SQL": "select * from t1 right join t2 on t1.a=t2.a",
+        "Plan": [
+          "IndexHashJoin 12487.50 root  right outer join, inner:IndexLookUp, outer key:test.t2.a, inner key:test.t1.a, equal cond:eq(test.t2.a, test.t1.a)",
+          "├─TableReader(Build) 10000.00 root  data:TableFullScan",
+          "│ └─TableFullScan 10000.00 cop[tikv] table:t2 keep order:false, stats:pseudo",
+          "└─IndexLookUp(Probe) 12487.50 root  ",
+          "  ├─Selection(Build) 12487.50 cop[tikv]  not(isnull(test.t1.a))",
+          "  │ └─IndexRangeScan 12500.00 cop[tikv] table:t1, index:a(a) range: decided by [eq(test.t1.a, test.t2.a)], keep order:false, stats:pseudo",
+          "  └─TableRowIDScan(Probe) 12487.50 cop[tikv] table:t1 keep order:false, stats:pseudo"
+        ],
+        "Warning": null
+      },
+      {
+        "SQL": "select /*+ hash_join(t1) */ * from t1, t2",
+        "Plan": [
+          "HashJoin 100000000.00 root  CARTESIAN inner join",
+          "├─TableReader(Build) 10000.00 root  data:TableFullScan",
+          "│ └─TableFullScan 10000.00 cop[tikv] table:t2 keep order:false, stats:pseudo",
+          "└─TableReader(Probe) 10000.00 root  data:TableFullScan",
+          "  └─TableFullScan 10000.00 cop[tikv] table:t1 keep order:false, stats:pseudo"
+        ],
+        "Warning": [
+          "Warning 1815 A conflict between the HASH_JOIN hint and the NO_HASH_JOIN hint, or the tidb_opt_enable_hash_join system variable, the HASH_JOIN hint will take precedence."
+        ]
+      },
+      {
+        "SQL": "select /*+ hash_join(t2) */ * from t1, t2",
+        "Plan": [
+          "HashJoin 100000000.00 root  CARTESIAN inner join",
+          "├─TableReader(Build) 10000.00 root  data:TableFullScan",
+          "│ └─TableFullScan 10000.00 cop[tikv] table:t2 keep order:false, stats:pseudo",
+          "└─TableReader(Probe) 10000.00 root  data:TableFullScan",
+          "  └─TableFullScan 10000.00 cop[tikv] table:t1 keep order:false, stats:pseudo"
+        ],
+        "Warning": [
+          "Warning 1815 A conflict between the HASH_JOIN hint and the NO_HASH_JOIN hint, or the tidb_opt_enable_hash_join system variable, the HASH_JOIN hint will take precedence."
+        ]
+      }
+    ]
+  },
+
   {
     "Name": "TestNoIndexJoinHint",
     "Cases": [

diff --git a/planner/core/exhaust_physical_plans.go b/planner/core/exhaust_physical_plans.go
@@ -244,7 +244,7 @@ func (p *LogicalJoin) GetMergeJoin(prop *property.PhysicalProperty, schema *expr
 	// If TiDB_SMJ hint is existed, it should consider enforce merge join,
 	// because we can't trust lhsChildProperty completely.
 	if (p.preferJoinType&preferMergeJoin) > 0 ||
-		(p.preferJoinType&preferNoHashJoin) > 0 { // if hash join is not allowed, generate as many other types of join as possible to avoid 'cant-find-plan' error.
+		p.shouldSkipHashJoin() { // if hash join is not allowed, generate as many other types of join as possible to avoid 'cant-find-plan' error.
 		joins = append(joins, p.getEnforcedMergeJoin(prop, schema, statsInfo)...)
 	}
 
@@ -391,6 +391,10 @@ var ForceUseOuterBuild4Test = atomic.NewBool(false)
 // TODO: use hint and remove this variable
 var ForcedHashLeftJoin4Test = atomic.NewBool(false)
 
+func (p *LogicalJoin) shouldSkipHashJoin() bool {
+	return (p.preferJoinType&preferNoHashJoin) > 0 || (p.SCtx().GetSessionVars().DisableHashJoin)
+}
+
 func (p *LogicalJoin) getHashJoins(prop *property.PhysicalProperty) (joins []PhysicalPlan, forced bool) {
 	if !prop.IsSortItemEmpty() { // hash join doesn't promise any orders
 		return
@@ -451,12 +455,12 @@ func (p *LogicalJoin) getHashJoins(prop *property.PhysicalProperty) (joins []Phy
 	}
 
 	forced = (p.preferJoinType&preferHashJoin > 0) || forceLeftToBuild || forceRightToBuild
-	noHashJoin := (p.preferJoinType & preferNoHashJoin) > 0
-	if !forced && noHashJoin {
+	if !forced && p.shouldSkipHashJoin() {
 		return nil, false
-	} else if forced && noHashJoin {
+	} else if forced && p.shouldSkipHashJoin() {
 		p.SCtx().GetSessionVars().StmtCtx.AppendWarning(ErrInternal.GenWithStack(
-			"Some HASH_JOIN and NO_HASH_JOIN hints conflict, NO_HASH_JOIN is ignored"))
+			"A conflict between the HASH_JOIN hint and the NO_HASH_JOIN hint, " +
+				"or the tidb_opt_enable_hash_join system variable, the HASH_JOIN hint will take precedence."))
 	}
 	return
 }

diff --git a/sessionctx/variable/session.go b/sessionctx/variable/session.go
@@ -1244,6 +1244,9 @@ type SessionVars struct {
 	// AnalyzeVersion indicates how TiDB collect and use analyzed statistics.
 	AnalyzeVersion int
 
+	// DisableHashJoin indicates whether to disable hash join.
+	DisableHashJoin bool
+
 	// EnableHistoricalStats indicates whether to enable historical statistics.
 	EnableHistoricalStats bool
 

diff --git a/sessionctx/variable/sysvar.go b/sessionctx/variable/sysvar.go
@@ -2093,6 +2093,10 @@ var defaultSysVars = []*SysVar{
 		s.AnalyzeVersion = tidbOptPositiveInt32(val, DefTiDBAnalyzeVersion)
 		return nil
 	}},
+	{Scope: ScopeGlobal | ScopeSession, Name: TiDBOptEnableHashJoin, Value: BoolToOnOff(DefTiDBOptEnableHashJoin), Type: TypeBool, SetSession: func(s *SessionVars, val string) error {
+		s.DisableHashJoin = !TiDBOptOn(val)
+		return nil
+	}},
 	{Scope: ScopeGlobal | ScopeSession, Name: TiDBEnableIndexMergeJoin, Value: BoolToOnOff(DefTiDBEnableIndexMergeJoin), Hidden: true, Type: TypeBool, SetSession: func(s *SessionVars, val string) error {
 		s.EnableIndexMergeJoin = TiDBOptOn(val)
 		return nil

diff --git a/sessionctx/variable/tidb_vars.go b/sessionctx/variable/tidb_vars.go
@@ -906,6 +906,9 @@ const (
 	// TiDBEnableCheckConstraint indicates whether to enable check constraint feature.
 	TiDBEnableCheckConstraint = "tidb_enable_check_constraint"
 
+	// TiDBOptEnableHashJoin indicates whether to enable hash join.
+	TiDBOptEnableHashJoin = "tidb_opt_enable_hash_join"
+
 	// TiDBOptObjective indicates whether the optimizer should be more stable, predictable or more aggressive.
 	// Please see comments of SessionVars.OptObjective for details.
 	TiDBOptObjective = "tidb_opt_objective"
@@ -1411,6 +1414,7 @@ const (
 	DefTiDBLockUnchangedKeys                          = true
 	DefTiDBEnableCheckConstraint                      = false
 	DefTiDBSkipMissingPartitionStats                  = true
+	DefTiDBOptEnableHashJoin                          = true
 	DefTiDBOptObjective                               = OptObjectiveModerate
 	DefTiDBSchemaVersionCacheLimit                    = 16
 )