executor, session: Add Detach() method to detach the record set

pkg/executor/BUILD.bazel

@@ -121,6 +121,7 @@ go_library(
         "//pkg/executor/lockstats",
         "//pkg/executor/metrics",
         "//pkg/executor/sortexec",
+        "//pkg/executor/staticrecordset",
         "//pkg/executor/unionexec",
         "//pkg/expression",
         "//pkg/expression/aggregation",

pkg/executor/adapter.go

@@ -35,6 +35,7 @@ import (
 	"github.com/pingcap/tidb/pkg/domain"
 	"github.com/pingcap/tidb/pkg/executor/internal/exec"
 	executor_metrics "github.com/pingcap/tidb/pkg/executor/metrics"
+	"github.com/pingcap/tidb/pkg/executor/staticrecordset"
 	"github.com/pingcap/tidb/pkg/expression"
 	"github.com/pingcap/tidb/pkg/infoschema"
 	"github.com/pingcap/tidb/pkg/keyspace"
@@ -241,6 +242,17 @@ func (a *recordSet) OnFetchReturned() {
 	a.stmt.LogSlowQuery(a.txnStartTS, len(a.lastErrs) == 0, true)
 }
 
+// Detach creates a new `RecordSet` which doesn't depend on the current session context.
+func (a *recordSet) TryDetach() (sqlexec.RecordSet, bool, error) {
+	// TODO: also detach the executor. Currently, the executor inside may contain the session context. Once
+	// the executor itself supports detach, we should also detach it here.
+	e, ok := a.executor.(*TableReaderExecutor)
+	if !ok {
+		return nil, false, nil
+	}
+	return staticrecordset.New(a.Fields(), e, a.stmt.GetTextToLog(false)), true, nil
+}
+
 // ExecStmt implements the sqlexec.Statement interface, it builds a planner.Plan to an sqlexec.Statement.
 type ExecStmt struct {
 	// GoCtx stores parent go context.Context for a stmt.

pkg/executor/staticrecordset/BUILD.bazel

@@ -0,0 +1,31 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_test")
+
+go_library(
+    name = "staticrecordset",
+    srcs = ["recordset.go"],
+    importpath = "github.com/pingcap/tidb/pkg/executor/staticrecordset",
+    visibility = ["//visibility:public"],
+    deps = [
+        "//pkg/executor/internal/exec",
+        "//pkg/parser/ast",
+        "//pkg/util",
+        "//pkg/util/chunk",
+        "//pkg/util/logutil",
+        "//pkg/util/sqlexec",
+        "@org_uber_go_zap//:zap",
+    ],
+)
+
+go_test(
+    name = "staticrecordset_test",
+    timeout = "short",
+    srcs = ["integration_test.go"],
+    flaky = True,
+    shard_count = 4,
+    deps = [
+        "//pkg/testkit",
+        "//pkg/util/sqlexec",
+        "@com_github_stretchr_testify//require",
+        "@com_github_tikv_client_go_v2//tikv",
+    ],
+)

pkg/executor/staticrecordset/integration_test.go

@@ -0,0 +1,150 @@
+// Copyright 2024 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,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package staticrecordset_test
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/pingcap/tidb/pkg/testkit"
+	"github.com/pingcap/tidb/pkg/util/sqlexec"
+	"github.com/stretchr/testify/require"
+	"github.com/tikv/client-go/v2/tikv"
+)
+
+func TestStaticRecordSet(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+
+	tk.MustExec("use test")
+	tk.MustExec("create table t(id int)")
+	tk.MustExec("insert into t values (1), (2), (3)")
+
+	rs, err := tk.Exec("select * from t")
+	require.NoError(t, err)
+	drs := rs.(sqlexec.DetachableRecordSet)
+	srs, ok, err := drs.TryDetach()
+	require.True(t, ok)
+	require.NoError(t, err)
+
+	// check schema
+	require.Len(t, srs.Fields(), 1)
+	require.Equal(t, "id", srs.Fields()[0].Column.Name.O)
+
+	// check data
+	chk := srs.NewChunk(nil)
+	err = srs.Next(context.Background(), chk)
+	require.NoError(t, err)
+	require.Equal(t, 3, chk.NumRows())
+	require.Equal(t, int64(1), chk.GetRow(0).GetInt64(0))
+	require.Equal(t, int64(2), chk.GetRow(1).GetInt64(0))
+	require.Equal(t, int64(3), chk.GetRow(2).GetInt64(0))
+
+	require.NoError(t, srs.Close())
+}
+
+func TestStaticRecordSetWithTxn(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+
+	tk.MustExec("use test")
+	tk.MustExec("create table t(id int)")
+	tk.MustExec("insert into t values (1), (2), (3)")
+
+	rs, err := tk.Exec("select * from t")
+	require.NoError(t, err)
+	txn, err := tk.Session().Txn(false)
+	require.NoError(t, err)
+	require.True(t, txn.Valid())
+	drs := rs.(sqlexec.DetachableRecordSet)
+	srs, ok, err := drs.TryDetach()
+	require.True(t, ok)
+	require.NoError(t, err)
+
+	// The transaction should have been committed.
+	txn, err = tk.Session().Txn(false)
+	require.NoError(t, err)
+	require.False(t, txn.Valid())
+
+	// Now, it's fine to run another statement on the session
+	// remove all existing data in the table
+	tk.MustExec("truncate table t")
+
+	// check data
+	chk := srs.NewChunk(nil)
+	err = srs.Next(context.Background(), chk)
+	require.NoError(t, err)
+	require.Equal(t, 3, chk.NumRows())
+	require.Equal(t, int64(1), chk.GetRow(0).GetInt64(0))
+	require.Equal(t, int64(2), chk.GetRow(1).GetInt64(0))
+	require.Equal(t, int64(3), chk.GetRow(2).GetInt64(0))
+
+	require.NoError(t, srs.Close())
+}
+
+func TestStaticRecordSetExceedGCTime(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+
+	tk.MustExec("use test")
+	tk.MustExec("create table t(id int)")
+	tk.MustExec("insert into t values (1), (2), (3)")
+
+	rs, err := tk.Exec("select * from t")
+	require.NoError(t, err)
+	// Get the startTS
+	txn, err := tk.Session().Txn(false)
+	require.NoError(t, err)
+	startTS := txn.StartTS()
+
+	// Detach the record set
+	drs := rs.(sqlexec.DetachableRecordSet)
+	srs, ok, err := drs.TryDetach()
+	require.True(t, ok)
+	require.NoError(t, err)
+
+	// Now, it's fine to run another statement on the session
+	// remove all existing data in the table
+	tk.MustExec("truncate table t")
+
+	// Update the safe point
+	store.(tikv.Storage).UpdateSPCache(startTS+1, time.Now())
+
+	// Check data, it'll get an error
+	chk := srs.NewChunk(nil)
+	err = srs.Next(context.Background(), chk)
+	require.Error(t, err)
+	require.NoError(t, srs.Close())
+}
+
+func TestDetachError(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+
+	tk.MustExec("use test")
+	tk.MustExec("create table t(id int)")
+	tk.MustExec("insert into t values (1), (2), (3)")
+
+	// explicit transaction is not allowed
+	tk.MustExec("begin")
+	rs, err := tk.Exec("select * from t")
+	require.NoError(t, err)
+	drs2 := rs.(sqlexec.DetachableRecordSet)
+	_, ok, err := drs2.TryDetach()
+	require.False(t, ok)
+	require.NoError(t, err)
+	tk.MustExec("commit")
+}

pkg/executor/staticrecordset/recordset.go

@@ -0,0 +1,79 @@
+// Copyright 2024 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,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package staticrecordset
+
+import (
+	"context"
+
+	"github.com/pingcap/tidb/pkg/executor/internal/exec"
+	"github.com/pingcap/tidb/pkg/parser/ast"
+	"github.com/pingcap/tidb/pkg/util"
+	"github.com/pingcap/tidb/pkg/util/chunk"
+	"github.com/pingcap/tidb/pkg/util/logutil"
+	"github.com/pingcap/tidb/pkg/util/sqlexec"
+	"go.uber.org/zap"
+)
+
+var _ sqlexec.RecordSet = &staticRecordSet{}
+
+type staticRecordSet struct {
+	fields   []*ast.ResultField
+	executor exec.Executor
+
+	sqlText string
+}
+
+// New creates a new staticRecordSet
+func New(fields []*ast.ResultField, executor exec.Executor, sqlText string) sqlexec.RecordSet {
+	return &staticRecordSet{
+		fields:   fields,
+		executor: executor,
+		sqlText:  sqlText,
+	}
+}
+
+func (s *staticRecordSet) Fields() []*ast.ResultField {
+	return s.fields
+}
+
+func (s *staticRecordSet) Next(ctx context.Context, req *chunk.Chunk) (err error) {
+	defer func() {
+		r := recover()
+		if r == nil {
+			return
+		}
+		err = util.GetRecoverError(r)
+		logutil.Logger(ctx).Error("execute sql panic", zap.String("sql", s.sqlText), zap.Stack("stack"))
+	}()
+
+	return exec.Next(ctx, s.executor, req)
+}
+
+// NewChunk create a chunk base on top-level executor's exec.NewFirstChunk().
+func (s *staticRecordSet) NewChunk(alloc chunk.Allocator) *chunk.Chunk {
+	if alloc == nil {
+		return exec.NewFirstChunk(s.executor)
+	}
+
+	return alloc.Alloc(s.executor.RetFieldTypes(), s.executor.InitCap(), s.executor.MaxChunkSize())
+}
+
+// Close closes the executor.
+func (s *staticRecordSet) Close() error {
+	err := exec.Close(s.executor)
+	s.executor = nil
+
+	return err
+}

pkg/session/session.go

@@ -2379,6 +2379,40 @@ func (rs *execStmtResult) Close() error {
 	return err2
 }
 
+func (rs *execStmtResult) TryDetach() (sqlexec.RecordSet, bool, error) {
+	if !rs.sql.IsReadOnly(rs.se.GetSessionVars()) {
+		return nil, false, nil
+	}
+	if !plannercore.IsAutoCommitTxn(rs.se.GetSessionVars()) {
+		return nil, false, nil
+	}
+
+	drs, ok := rs.RecordSet.(sqlexec.DetachableRecordSet)
+	if !ok {
+		return nil, false, nil
+	}
+	detachedRS, ok, err := drs.TryDetach()
+	if !ok || err != nil {
+		return nil, ok, err
+	}
+
+	// FIXME: block the min-start-ts. Now the `min-start-ts` will advance and exceed the `startTS` used by
+	// this detached record set, and may cause an error if `GC` runs.
+
+	// Now, a transaction is not needed for the detached record set, so we commit the transaction and cleanup
+	// the session state.
+	err = finishStmt(context.Background(), rs.se, nil, rs.sql)
+	if err != nil {
+		err2 := detachedRS.Close()
+		if err2 != nil {
+			logutil.BgLogger().Error("close detached record set failed", zap.Error(err2))
+		}
+		return nil, false, err
+	}
+
+	return detachedRS, true, nil
+}
+
 // rollbackOnError makes sure the next statement starts a new transaction with the latest InfoSchema.
 func (s *session) rollbackOnError(ctx context.Context) {
 	if !s.sessionVars.InTxn() {

pkg/util/sqlexec/restricted_sql_executor.go

@@ -199,6 +199,22 @@ type RecordSet interface {
 	Close() error
 }
 
+// DetachableRecordSet extends the `RecordSet` to support detaching from current session context
+type DetachableRecordSet interface {
+	RecordSet
+
+	// TryDetach detaches the record set from the current session context.
+	//
+	// The last two return value indicates whether the record set is suitable for detaching, and whether
+	// it detaches successfully. If it faces any error during detaching (and there is no way to rollback),
+	// it will return the error. If an error is returned, the record set (and session) will be left at
+	// an unknown state.
+	//
+	// If the caller receives `_, false, _`, it means the original record set can still be used. If the caller
+	// receives an error, it means the original record set (and the session) is dirty.
+	TryDetach() (RecordSet, bool, error)
+}
+
 // MultiQueryNoDelayResult is an interface for one no-delay result for one statement in multi-queries.
 type MultiQueryNoDelayResult interface {
 	// AffectedRows return affected row for one statement in multi-queries.