From 47bdf0fcb57d15bd2800a92bd286551d6561d1d5 Mon Sep 17 00:00:00 2001
From: shunki-fujita <shunki-fujita@cybozu.co.jp>
Date: Fri, 5 Jul 2024 08:31:25 +0000
Subject: [PATCH] issue-708: Set lock_wait_timeout to SetReadOnly

---
 clustering/operations.go | 30 ++++++++++++++++++++++++------
 pkg/dbop/nop.go          |  4 ++++
 pkg/dbop/operator.go     |  3 +++
 pkg/dbop/replication.go  |  7 +++++++
 4 files changed, 38 insertions(+), 6 deletions(-)

diff --git a/clustering/operations.go b/clustering/operations.go
index 4c149ced0..2d52ad81e 100644
--- a/clustering/operations.go
+++ b/clustering/operations.go
@@ -149,14 +149,32 @@ func (p *managerProcess) clone(ctx context.Context, ss *StatusSet) (bool, error)
 func (p *managerProcess) switchover(ctx context.Context, ss *StatusSet) error {
 	log := logFromContext(ctx)
 	log.Info("begin switchover the primary", "current", ss.Primary, "next", ss.Candidate)
-
 	pdb := ss.DBOps[ss.Primary]
-	if err := pdb.SetReadOnly(ctx, true); err != nil {
-		return fmt.Errorf("failed to make instance %d read-only: %w", ss.Primary, err)
+
+	// SetReadOnly waits for a running DML.
+	// Therefore, if it waits for a long time, deleteGracePeriodSeconds may be reached.
+	// To avoid this, set lock_wait_timeout to a short time temporarily.
+	// If SetReadOnly fails, kill all processes and retry.
+	succeeded := false
+	if err := pdb.SetSessionLockWaitTimeout(ctx, 15); err != nil {
+		return fmt.Errorf("failed to set lock_wait_timeout: %w", err)
+	}
+	for i := 0; i < 2; i++ {
+		if err := pdb.SetReadOnly(ctx, true); err != nil {
+			log.Error(err, "failed to set read-only mode", "instance", ss.Primary)
+		} else {
+			succeeded = true
+		}
+		time.Sleep(100 * time.Millisecond)
+		if err := pdb.KillConnections(ctx); err != nil {
+			return fmt.Errorf("failed to kill connections in instance %d: %w", ss.Primary, err)
+		}
+		if succeeded {
+			break
+		}
 	}
-	time.Sleep(100 * time.Millisecond)
-	if err := pdb.KillConnections(ctx); err != nil {
-		return fmt.Errorf("failed to kill connections in instance %d: %w", ss.Primary, err)
+	if !succeeded {
+		return fmt.Errorf("failed to set read-only mode in instance %d", ss.Primary)
 	}
 	pst, err := pdb.GetStatus(ctx)
 	if err != nil {
diff --git a/pkg/dbop/nop.go b/pkg/dbop/nop.go
index a07191cf7..b19a84be5 100644
--- a/pkg/dbop/nop.go
+++ b/pkg/dbop/nop.go
@@ -51,6 +51,10 @@ func (o NopOperator) WaitForGTID(ctx context.Context, gtidSet string, timeoutSec
 	return ErrNop
 }
 
+func (o NopOperator) SetSessionLockWaitTimeout(ctx context.Context, timeoutSeconds int) error {
+	return ErrNop
+}
+
 func (o NopOperator) SetReadOnly(context.Context, bool) error {
 	return ErrNop
 }
diff --git a/pkg/dbop/operator.go b/pkg/dbop/operator.go
index 855703373..5d4592d17 100644
--- a/pkg/dbop/operator.go
+++ b/pkg/dbop/operator.go
@@ -54,6 +54,9 @@ type Operator interface {
 	// If `timeoutSeconds` is zero, this will not timeout.
 	WaitForGTID(ctx context.Context, gtidSet string, timeoutSeconds int) error
 
+	// SetSessionLockWaitTimeout set @@session.lock_wait_timeout to `timeoutSeconds`.
+	SetSessionLockWaitTimeout(ctx context.Context, timeoutSeconds int) error
+
 	// SetReadOnly makes the instance super_read_only if `true` is passed.
 	// Otherwise, this stops the replication and makes the instance writable.
 	SetReadOnly(context.Context, bool) error
diff --git a/pkg/dbop/replication.go b/pkg/dbop/replication.go
index 999d67b53..cf7cb97c2 100644
--- a/pkg/dbop/replication.go
+++ b/pkg/dbop/replication.go
@@ -71,6 +71,13 @@ func (o *operator) WaitForGTID(ctx context.Context, gtid string, timeoutSeconds
 	return nil
 }
 
+func (o *operator) SetSessionLockWaitTimeout(ctx context.Context, timeoutSeconds int)  error {
+	if _, err := o.db.ExecContext(ctx, "SET SESSION lock_wait_timeout=?", timeoutSeconds); err != nil {
+		return fmt.Errorf("failed to set lock_wait_timeout: %w", err)
+	}
+	return nil
+}
+
 func (o *operator) SetReadOnly(ctx context.Context, readOnly bool) error {
 	if readOnly {
 		if _, err := o.db.ExecContext(ctx, "SET GLOBAL super_read_only=1"); err != nil {