Disconnect chained replicas when the replica performs PSYNC with the master always to avoid replication offset mismatch between master and chained replicas.

Author: QuChen88

src/replication.c

@@ -2023,12 +2023,19 @@ int slaveTryPartialResynchronization(connection *conn, int read_reply) {
                  * new one. */
                 memcpy(server.replid,new,sizeof(server.replid));
                 memcpy(server.cached_master->replid,new,sizeof(server.replid));
-
-                /* Disconnect all the sub-slaves: they need to be notified. */
-                disconnectSlaves();
             }
         }
 
+        /* Disconnect all the sub-replicas: they need to be notified always because
+         * in case the master has last replicated some non-meaningful commands
+         * (e.g. PINGs), the primary replica will request the PSYNC offset for the
+         * last known meaningful command. This means the master will again replicate
+         * the non-meaningful commands. If the sub-replicas still remains connected,
+         * they will receive those commands a second time and increment the master
+         * replication offset to be higher than the master's offset forever.
+         */
+        disconnectSlaves();
+
         /* Setup the replication to continue. */
         sdsfree(reply);
         replicationResurrectCachedMaster(conn);

tests/integration/psync2-pingoff.tcl

@@ -60,3 +60,53 @@ start_server {} {
         }
     }
 }}
+
+
+start_server {tags {"psync2"}} {
+start_server {} {
+start_server {} {
+
+    for {set j 0} {$j < 3} {incr j} {
+        set R($j) [srv [expr 0-$j] client]
+        set R_host($j) [srv [expr 0-$j] host]
+        set R_port($j) [srv [expr 0-$j] port]
+        $R($j) CONFIG SET repl-ping-replica-period 1
+    }
+
+    test "Chained replicas disconnect when replica re-connect with the same master" {
+        # Add a second replica as a chained replica of the current replica
+        $R(1) replicaof $R_host(0) $R_port(0)
+        $R(2) replicaof $R_host(1) $R_port(1)
+        wait_for_condition 50 1000 {
+            [status $R(2) master_link_status] == "up"
+        } else {
+            fail "Chained replica not replicating from its master"
+        }
+
+        # Do a write on the master, and wait for 3 seconds for the master to
+        # send some PINGs to its replica
+        $R(0) INCR counter2
+        after 2000
+        set sync_partial_master [status $R(0) sync_partial_ok]
+        set sync_partial_replica [status $R(1) sync_partial_ok]
+        $R(0) CONFIG SET repl-ping-replica-period 100
+
+        # Disconnect the master's direct replica
+        $R(0) client kill type replica
+        wait_for_condition 50 1000 {
+            [status $R(1) master_link_status] == "up" && 
+            [status $R(2) master_link_status] == "up" &&
+            [status $R(0) sync_partial_ok] == $sync_partial_master + 1 &&
+            [status $R(1) sync_partial_ok] == $sync_partial_replica + 1
+        } else {
+            fail "Disconnected replica failed to PSYNC with master"
+        }
+
+        # Verify that the replica and its replica's meaningful and real
+        # offsets match with the master
+        assert_equal [status $R(0) master_repl_offset] [status $R(1) master_repl_offset]
+        assert_equal [status $R(0) master_repl_offset] [status $R(2) master_repl_offset]
+        assert_equal [status $R(0) master_repl_meaningful_offset] [status $R(1) master_repl_meaningful_offset]
+        assert_equal [status $R(0) master_repl_meaningful_offset] [status $R(2) master_repl_meaningful_offset]
+    }
+}}}