*: add a blacklist to disallow pushing down specific expressions (#10688)

executor/builder.go

@@ -84,6 +84,8 @@ func (b *executorBuilder) build(p plannercore.Plan) Executor {
 		return b.buildCheckIndexRange(v)
 	case *plannercore.ChecksumTable:
 		return b.buildChecksumTable(v)
+	case *plannercore.ReloadExprPushdownBlacklist:
+		return b.buildReloadExprPushdownBlacklist(v)
 	case *plannercore.DDL:
 		return b.buildDDL(v)
 	case *plannercore.Deallocate:
@@ -426,6 +428,10 @@ func (b *executorBuilder) buildChecksumTable(v *plannercore.ChecksumTable) Execu
 	return e
 }
 
+func (b *executorBuilder) buildReloadExprPushdownBlacklist(v *plannercore.ReloadExprPushdownBlacklist) Executor {
+	return &ReloadExprPushdownBlacklistExec{baseExecutor{ctx: b.ctx}}
+}
+
 func (b *executorBuilder) buildDeallocate(v *plannercore.Deallocate) Executor {
 	base := newBaseExecutor(b.ctx, nil, v.ExplainID())
 	base.initCap = chunk.ZeroCapacity

executor/reload_expr_pushdown_blacklist.go

@@ -0,0 +1,50 @@
+// Copyright 2019 PingCAP, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package executor
+
+import (
+	"context"
+	"strings"
+
+	"github.com/pingcap/tidb/expression"
+	"github.com/pingcap/tidb/sessionctx"
+	"github.com/pingcap/tidb/util/chunk"
+	"github.com/pingcap/tidb/util/sqlexec"
+)
+
+// ReloadExprPushdownBlacklistExec indicates ReloadExprPushdownBlacklist executor.
+type ReloadExprPushdownBlacklistExec struct {
+	baseExecutor
+}
+
+// Next implements the Executor Next interface.
+func (e *ReloadExprPushdownBlacklistExec) Next(ctx context.Context, _ *chunk.Chunk) error {
+	return LoadExprPushdownBlacklist(e.ctx)
+}
+
+// LoadExprPushdownBlacklist loads the latest data from table mysql.expr_pushdown_blacklist.
+func LoadExprPushdownBlacklist(ctx sessionctx.Context) (err error) {
+	sql := "select HIGH_PRIORITY name from mysql.expr_pushdown_blacklist"
+	rows, _, err := ctx.(sqlexec.RestrictedSQLExecutor).ExecRestrictedSQL(ctx, sql)
+	if err != nil {
+		return err
+	}
+	newBlacklist := make(map[string]struct{})
+	for _, row := range rows {
+		name := row.GetString(0)
+		newBlacklist[strings.ToLower(name)] = struct{}{}
+	}
+	expression.DefaultExprPushdownBlacklist.Store(newBlacklist)
+	return nil
+}

executor/reload_expr_pushdown_blacklist_test.go

@@ -0,0 +1,42 @@
+// Copyright 2019 PingCAP, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package executor_test
+
+import (
+	. "github.com/pingcap/check"
+	"github.com/pingcap/tidb/util/testkit"
+)
+
+func (s *testSuite) TestReloadExprPushdownBlacklist(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("create database expr_pushdown_blacklist")
+	tk.MustExec("use expr_pushdown_blacklist")
+	tk.MustExec("create table t (a int)")
+	tk.MustQuery("desc select * from t where a < 1").Check(testkit.Rows(
+		"TableReader_7 3323.33 root data:Selection_6",
+		"└─Selection_6 3323.33 cop lt(expr_pushdown_blacklist.t.a, 1)",
+		"  └─TableScan_5 10000.00 cop table:t, range:[-inf,+inf], keep order:false, stats:pseudo"))
+
+	tk.MustExec("insert into mysql.expr_pushdown_blacklist values('lt')")
+	tk.MustQuery("desc select * from t where a < 1").Check(testkit.Rows(
+		"TableReader_7 3323.33 root data:Selection_6",
+		"└─Selection_6 3323.33 cop lt(expr_pushdown_blacklist.t.a, 1)",
+		"  └─TableScan_5 10000.00 cop table:t, range:[-inf,+inf], keep order:false, stats:pseudo"))
+
+	tk.MustExec("admin reload expr_pushdown_blacklist")
+	tk.MustQuery("desc select * from t where a < 1").Check(testkit.Rows(
+		"Selection_5 8000.00 root lt(expr_pushdown_blacklist.t.a, 1)",
+		"└─TableReader_7 10000.00 root data:TableScan_6",
+		"  └─TableScan_6 10000.00 cop table:t, range:[-inf,+inf], keep order:false, stats:pseudo"))
+}

expression/expr_to_pb.go

@@ -15,6 +15,7 @@ package expression
 
 import (
 	"context"
+	"sync/atomic"
 
 	"github.com/pingcap/parser/ast"
 	"github.com/pingcap/parser/charset"
@@ -321,8 +322,16 @@ func (pc PbConverter) canFuncBePushed(sf *ScalarFunction) bool {
 
 		// date functions.
 		ast.DateFormat:
-
-		return true
+		_, disallowPushdown := DefaultExprPushdownBlacklist.Load().(map[string]struct{})[sf.FuncName.L]
+		return true && !disallowPushdown
 	}
 	return false
 }
+
+// DefaultExprPushdownBlacklist indicates the expressions which can not be pushed down to TiKV.
+var DefaultExprPushdownBlacklist *atomic.Value
+
+func init() {
+	DefaultExprPushdownBlacklist = new(atomic.Value)
+	DefaultExprPushdownBlacklist.Store(make(map[string]struct{}))
+}

expression/integration_test.go

@@ -4155,3 +4155,8 @@ func (s *testIntegrationSuite) TestDaynameArithmetic(c *C) {
 		tk.MustQuery(c.sql).Check(testkit.Rows(c.result))
 	}
 }
+
+func (s *testIntegrationSuite) TestExprPushdownBlacklist(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustQuery(`select * from mysql.expr_pushdown_blacklist`).Check(testkit.Rows())
+}

go.mod

@@ -79,3 +79,5 @@ require (
 	gopkg.in/natefinch/lumberjack.v2 v2.0.0
 	gopkg.in/tomb.v1 v1.0.0-20141024135613-dd632973f1e7 // indirect
 )
+
+replace github.com/pingcap/parser => github.com/XuHuaiyu/parser v0.0.0-20190701025952-1a27d824ea1d