From 3056f41c48c39fa00ebd45814c19f8df88b4ada9 Mon Sep 17 00:00:00 2001
From: lhy1024 <lhylhy1024@gmail.com>
Date: Fri, 26 Dec 2025 23:37:25 +0800
Subject: [PATCH] ddl: fix affinity idempotency problem (#65291)

ref pingcap/tidb#64938
---
 pkg/ddl/affinity_test.go | 22 ++++++++++++++++++----
 pkg/ddl/table.go         |  8 ++++++--
 2 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/pkg/ddl/affinity_test.go b/pkg/ddl/affinity_test.go
index 5c85439a04..595330f239 100644
--- a/pkg/ddl/affinity_test.go
+++ b/pkg/ddl/affinity_test.go
@@ -173,9 +173,12 @@ func checkAffinityGroupsInPD(t *testing.T, do *domain.Domain, dbName, tbName str
 func TestAffinityPDInteraction(t *testing.T) {
 	store, dom := testkit.CreateMockStoreAndDomain(t)
 	tk := testkit.NewTestKit(t, store)
-
 	tk.MustExec("use test")
-	tk.MustExec("drop table if exists t1, t2, tp1, tp2")
+	dropTable := func() {
+		tk.MustExec("drop table if exists t1, t2, t3, tp1, tp2, tp3")
+	}
+	dropTable()
+	defer dropTable()
 
 	// Test 1: Create table with affinity='table'
 	tk.MustExec("create table t1(a int) affinity = 'table'")
@@ -237,8 +240,19 @@ func TestAffinityPDInteraction(t *testing.T) {
 	require.NoError(t, err)
 	require.Empty(t, groups, "old partition's affinity group should be deleted after truncate partition")
 
-	// Cleanup
-	tk.MustExec("drop table if exists t2, tp1, tp2")
+	// Test 8: ALTER TABLE AFFINITY idempotency - partition -> partition
+	tk.MustExec("create table tp3(a int) affinity = 'partition' partition by hash(a) partitions 3")
+	checkAffinityGroupsInPD(t, dom, "test", "tp3", true)
+	// Set affinity to partition again (idempotent operation)
+	tk.MustExec("alter table tp3 affinity = 'partition'")
+	checkAffinityGroupsInPD(t, dom, "test", "tp3", true)
+
+	// Test 9: ALTER TABLE AFFINITY idempotency - table -> table
+	tk.MustExec("create table t3(a int) affinity = 'table'")
+	checkAffinityGroupsInPD(t, dom, "test", "t3", true)
+	// Set affinity to table again (idempotent operation)
+	tk.MustExec("alter table t3 affinity = 'table'")
+	checkAffinityGroupsInPD(t, dom, "test", "t3", true)
 }
 
 func TestAffinityDropDatabase(t *testing.T) {
diff --git a/pkg/ddl/table.go b/pkg/ddl/table.go
index 35896d3de9..00aa2e9a3b 100644
--- a/pkg/ddl/table.go
+++ b/pkg/ddl/table.go
@@ -1778,9 +1778,13 @@ func onAlterTableAffinity(jobCtx *jobContext, job *model.Job) (ver int64, err er
 	// Delete old affinity groups (best-effort cleanup - ignore errors)
 	// ALTER TABLE AFFINITY: only delete when old table had affinity configuration
 	// This ensures 'ALTER TABLE AFFINITY = 'none'' correctly cleans up stale affinity groups
+	// Skip deletion if the affinity level remains the same to ensure idempotency
 	if oldTblInfo.Affinity != nil {
-		if err := deleteTableAffinityGroupsInPD(jobCtx, oldTblInfo, nil); err != nil {
-			logutil.DDLLogger().Error("failed to delete old affinity groups from PD", zap.Error(err), zap.Int64("tableID", oldTblInfo.ID))
+		// Only delete if affinity is removed or level changed (same level means same group IDs)
+		if tblInfo.Affinity == nil || oldTblInfo.Affinity.Level != tblInfo.Affinity.Level {
+			if err := deleteTableAffinityGroupsInPD(jobCtx, oldTblInfo, nil); err != nil {
+				logutil.DDLLogger().Error("failed to delete old affinity groups from PD", zap.Error(err), zap.Int64("tableID", oldTblInfo.ID))
+			}
 		}
 	}