Remove dual-channel-replication Feature Flag's Protection

src/config.c

@@ -3074,7 +3074,7 @@ standardConfig static_configs[] = {
     createBoolConfig("lazyfree-lazy-user-flush", NULL, DEBUG_CONFIG | MODIFIABLE_CONFIG, server.lazyfree_lazy_user_flush, 0, NULL, NULL),
     createBoolConfig("repl-disable-tcp-nodelay", NULL, MODIFIABLE_CONFIG, server.repl_disable_tcp_nodelay, 0, NULL, NULL),
     createBoolConfig("repl-diskless-sync", NULL, DEBUG_CONFIG | MODIFIABLE_CONFIG, server.repl_diskless_sync, 1, NULL, NULL),
-    createBoolConfig("dual-channel-replication-enabled", NULL, DEBUG_CONFIG | MODIFIABLE_CONFIG | PROTECTED_CONFIG, server.dual_channel_replication, 0, NULL, NULL),
+    createBoolConfig("dual-channel-replication-enabled", NULL, DEBUG_CONFIG | MODIFIABLE_CONFIG, server.dual_channel_replication, 0, NULL, NULL),
     createBoolConfig("aof-rewrite-incremental-fsync", NULL, MODIFIABLE_CONFIG, server.aof_rewrite_incremental_fsync, 1, NULL, NULL),
     createBoolConfig("no-appendfsync-on-rewrite", NULL, MODIFIABLE_CONFIG, server.aof_no_fsync_on_rewrite, 0, NULL, NULL),
     createBoolConfig("cluster-require-full-coverage", NULL, MODIFIABLE_CONFIG, server.cluster_require_full_coverage, 1, NULL, NULL),

tests/integration/dual-channel-replication.tcl

@@ -199,6 +199,7 @@ start_server {tags {"dual-channel-replication external:skip"}} {
 
             test "Toggle dual-channel-replication-enabled: $enable start" {    
                 populate 1000 primary 10000
+                $primary config set rdb-key-save-delay 0
                 set prev_sync_full [s 0 sync_full]
                 set prev_sync_partial [s 0 sync_partial_ok]
 
@@ -251,6 +252,63 @@ start_server {tags {"dual-channel-replication external:skip"}} {
                 }
                 $replica replicaof no one
             }
+
+            foreach test_instance {primary replica} {
+                $primary config set dual-channel-replication-enabled $enable
+                $replica config set dual-channel-replication-enabled $enable
+                test "Online toggle dual-channel-replication-enabled on $test_instance, starting with '$enable'" {    
+                    populate 1000 primary 10000
+                    $primary config set rdb-key-save-delay 100000   
+
+                    $replica replicaof $primary_host $primary_port
+                    # wait for sync to start
+                    if {$enable == "yes"} {
+                        wait_for_condition 500 1000 {
+                            [string match "*slave*,state=wait_bgsave*,type=rdb-channel*" [$primary info replication]] &&
+                            [string match "*slave*,state=bg_transfer*,type=main-channel*" [$primary info replication]] &&
+                            [s 0 rdb_bgsave_in_progress] eq 1
+                        } else {
+                            fail "replica didn't start a dual-channel sync session in time"
+                        }
+                    } else {
+                        wait_for_condition 500 1000 {
+                            [string match "*slave*,state=wait_bgsave*,type=replica*" [$primary info replication]] &&
+                            [s 0 rdb_bgsave_in_progress] eq 1
+                        } else {
+                            fail "replica didn't start a normal full sync session in time"
+                        }
+                    }
+                    # Toggle config
+                    set new_value "yes"
+                    if {$enable == "yes"} {
+                        set new_value "no"
+                    }
+                    set instance $primary
+                    if {$test_instance == "replica"} {
+                        set instance $replica
+                    }
+                    $instance config set dual-channel-replication-enabled $new_value
+                    # Wait for at least one server cron
+                    after 1000
+
+                    if {$enable == "yes"} {
+                        # Verify that dual channel replication sync is still in progress
+                        assert [string match "*slave*,state=wait_bgsave*,type=rdb-channel*" [$primary info replication]]
+                        assert [string match "*slave*,state=bg_transfer*,type=main-channel*" [$primary info replication]]
+                        assert {[s 0 rdb_bgsave_in_progress] eq 1}
+                    } else {
+                        # Verify that normal sync is still in progress
+                        assert [string match "*slave*,state=wait_bgsave*,type=replica*" [$primary info replication]]
+                        assert {[s 0 rdb_bgsave_in_progress] eq 1}
+                    }
+                    $replica replicaof no one
+                    wait_for_condition 500 1000 {
+                        [s -1 rdb_bgsave_in_progress] eq 0
+                    } else {
+                        fail "Primary should abort sync"
+                    }
+                }
+            }
         }
     }
 }

valkey.conf

@@ -687,6 +687,11 @@ repl-diskless-load disabled
 # memory to accommodate the buffer during synchronization. However, this tradeoff is 
 # generally beneficial as it prevents potential performance degradation on the primary 
 # server, which is typically handling more critical operations.
+#
+# When toggling this configuration on or off during an ongoing synchronization process,
+# it does not change the already running sync method. The new configuration will take
+# effect only for subsequent synchronization processes.
+
 dual-channel-replication-enabled no
 
 # Master send PINGs to its replicas in a predefined interval. It's possible to