ddl: Do not physical drop table after tiflash replica is set to 0 (#9440

)

close #9438

ddl: Do not physical drop table after tiflash replica is set to 0
To avoid a potential data loss issue when altering tiflash replica

dbms/src/TiDB/Schema/SchemaBuilder.cpp

@@ -391,7 +391,6 @@ void SchemaBuilder<Getter, NameMapper>::applySetTiFlashReplica(DatabaseID databa
     auto & tmt_context = context.getTMTContext();
     if (table_info->replica_info.count == 0)
     {
-        // Replicat number is to 0, mark the table as tombstone in TiFlash
         auto storage = tmt_context.getStorages().get(keyspace_id, table_info->id);
         if (unlikely(storage == nullptr))
         {
@@ -402,7 +401,14 @@ void SchemaBuilder<Getter, NameMapper>::applySetTiFlashReplica(DatabaseID databa
             return;
         }
 
-        applyDropTable(database_id, table_id, "SetTiFlashReplica-0");
+        // We can not mark the table is safe to be physically drop from the tiflash instances when
+        // the number of tiflash replica is set to be 0.
+        // There could be a concurrent issue that cause data loss. Check the following link for details:
+        // https://github.com/pingcap/tiflash/issues/9438#issuecomment-2360370761
+        // applyDropTable(database_id, table_id, "SetTiFlashReplica-0");
+
+        // Now only update the replica number to be 0 instead
+        updateTiFlashReplicaNumOnStorage(database_id, table_id, storage, table_info);
         return;
     }
 

tests/fullstack-test2/ddl/alter_table_tiflash_replica.test

@@ -82,13 +82,11 @@ mysql> set session tidb_isolation_read_engines='tiflash';select * from test.t;
 | x  |
 +----+
 |  1 |
-+----+
 |  8 |
-+----+
 | 50 |
 +----+
 
 >> DBGInvoke get_partition_tables_tiflash_replica_count("test", "t")
 ┌─get_partition_tables_tiflash_replica_count(test, t)─┐
 │ 1/1/1/                                              │
-└─────────────────────────────────────────────────────┘
+└─────────────────────────────────────────────────────┘