From 6854e606982a7e886591f44e2dfdb821bcd9c57c Mon Sep 17 00:00:00 2001
From: yibin <huyibin@pingcap.cn>
Date: Thu, 25 Jul 2024 09:54:05 +0800
Subject: [PATCH] session, config, sessionctx, executor: Set
 tidb_opt_projection_push_down to false when tidb upgrades from versions older
 than 8.3.0 to 8.3.0 and later (#54861)

ref pingcap/tidb#51876
---
 pkg/config/config.go                 |  7 ++++---
 pkg/executor/set_test.go             | 10 ++++++++++
 pkg/session/bootstrap.go             |  4 ++++
 pkg/sessionctx/variable/sysvar.go    |  2 +-
 pkg/sessionctx/variable/tidb_vars.go |  1 +
 5 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/pkg/config/config.go b/pkg/config/config.go
index 419d048f417e4..3534f06b0a2e6 100644
--- a/pkg/config/config.go
+++ b/pkg/config/config.go
@@ -711,9 +711,7 @@ type Performance struct {
 	TCPNoDelay          bool    `toml:"tcp-no-delay" json:"tcp-no-delay"`
 	CrossJoin           bool    `toml:"cross-join" json:"cross-join"`
 	DistinctAggPushDown bool    `toml:"distinct-agg-push-down" json:"distinct-agg-push-down"`
-	// Whether enable projection push down for coprocessors (both tikv & tiflash), default false.
-	ProjectionPushDown bool   `toml:"projection-push-down" json:"projection-push-down"`
-	MaxTxnTTL          uint64 `toml:"max-txn-ttl" json:"max-txn-ttl"`
+	MaxTxnTTL           uint64  `toml:"max-txn-ttl" json:"max-txn-ttl"`
 	// Deprecated
 	MemProfileInterval string `toml:"-" json:"-"`
 
@@ -754,6 +752,9 @@ type Performance struct {
 
 	// ConcurrentlyInitStats indicates whether to use concurrency to init stats.
 	ConcurrentlyInitStats bool `toml:"concurrently-init-stats" json:"concurrently-init-stats"`
+
+	// Deprecated: this config will not have any effect
+	ProjectionPushDown bool `toml:"projection-push-down" json:"projection-push-down"`
 }
 
 // PlanCache is the PlanCache section of the config.
diff --git a/pkg/executor/set_test.go b/pkg/executor/set_test.go
index 9068a1a195c04..e350d0264dff8 100644
--- a/pkg/executor/set_test.go
+++ b/pkg/executor/set_test.go
@@ -967,6 +967,16 @@ func TestSetVar(t *testing.T) {
 	tk.MustQuery("select @@session.tidb_txn_entry_size_limit, @@global.tidb_txn_entry_size_limit").Check(testkit.Rows("2048 4096"))
 	tk.MustExec("set global tidb_txn_entry_size_limit = 0")
 	tk.MustQuery("select @@session.tidb_txn_entry_size_limit, @@global.tidb_txn_entry_size_limit").Check(testkit.Rows("2048 0"))
+
+	// test for tidb_opt_projection_push_down
+	tk.MustQuery("select @@session.tidb_opt_projection_push_down, @@global.tidb_opt_projection_push_down").Check(testkit.Rows("1 1"))
+	tk.MustExec("set global tidb_opt_projection_push_down = 'OFF'")
+	tk.MustQuery("select @@session.tidb_opt_projection_push_down, @@global.tidb_opt_projection_push_down").Check(testkit.Rows("1 0"))
+	tk.MustExec("set session tidb_opt_projection_push_down = 'OFF'")
+	tk.MustQuery("select @@session.tidb_opt_projection_push_down, @@global.tidb_opt_projection_push_down").Check(testkit.Rows("0 0"))
+	tk.MustExec("set global tidb_opt_projection_push_down = 'on'")
+	tk.MustQuery("select @@session.tidb_opt_projection_push_down, @@global.tidb_opt_projection_push_down").Check(testkit.Rows("0 1"))
+	require.Error(t, tk.ExecToErr("set global tidb_opt_projection_push_down = 'UNKNOWN'"))
 }
 
 func TestSetCollationAndCharset(t *testing.T) {
diff --git a/pkg/session/bootstrap.go b/pkg/session/bootstrap.go
index a0f5bb51d34a4..adaae4cdb5f91 100644
--- a/pkg/session/bootstrap.go
+++ b/pkg/session/bootstrap.go
@@ -3065,6 +3065,10 @@ func upgradeToVer210(s sessiontypes.Session, ver int64) {
 	// Check if tidb_analyze_column_options exists in mysql.GLOBAL_VARIABLES.
 	// If not, set tidb_analyze_column_options to ALL since this is the old behavior before we introduce this variable.
 	initGlobalVariableIfNotExists(s, variable.TiDBAnalyzeColumnOptions, model.AllColumns.String())
+
+	// Check if tidb_opt_projection_push_down exists in mysql.GLOBAL_VARIABLES.
+	// If not, set tidb_opt_projection_push_down to Off since this is the old behavior before we introduce this variable.
+	initGlobalVariableIfNotExists(s, variable.TiDBOptProjectionPushDown, variable.Off)
 }
 
 func upgradeToVer211(s sessiontypes.Session, ver int64) {
diff --git a/pkg/sessionctx/variable/sysvar.go b/pkg/sessionctx/variable/sysvar.go
index f3fb13dee7ef6..b4e5dacb9dc31 100644
--- a/pkg/sessionctx/variable/sysvar.go
+++ b/pkg/sessionctx/variable/sysvar.go
@@ -211,7 +211,7 @@ var defaultSysVars = []*SysVar{
 		}
 		return nil
 	}},
-	{Scope: ScopeSession, Name: TiDBOptProjectionPushDown, Value: BoolToOnOff(config.GetGlobalConfig().Performance.ProjectionPushDown), Type: TypeBool, SetSession: func(s *SessionVars, val string) error {
+	{Scope: ScopeGlobal | ScopeSession, Name: TiDBOptProjectionPushDown, Value: BoolToOnOff(DefOptEnableProjectionPushDown), Type: TypeBool, SetSession: func(s *SessionVars, val string) error {
 		s.AllowProjectionPushDown = TiDBOptOn(val)
 		return nil
 	}},
diff --git a/pkg/sessionctx/variable/tidb_vars.go b/pkg/sessionctx/variable/tidb_vars.go
index cf073f1a2430d..2dc5792824058 100644
--- a/pkg/sessionctx/variable/tidb_vars.go
+++ b/pkg/sessionctx/variable/tidb_vars.go
@@ -1507,6 +1507,7 @@ const (
 	DefGroupConcatMaxLen                              = uint64(1024)
 	DefDefaultWeekFormat                              = "0"
 	DefTiDBEnableLazyCursorFetch                      = false
+	DefOptEnableProjectionPushDown                    = true
 )
 
 // Process global variables.