Redis-cli gets RDB by RDB channel (#13809)

Now we have RDB channel in https://github.com/redis/redis/pull/13732,
child process can transfer RDB in a background method, instead of
handled by main thread. So when redis-cli gets RDB from server, we can
adopt this way to reduce the main thread load.

---------

Co-authored-by: Ozan Tezcan <ozantezcan@gmail.com>

src/rdb.c

@@ -3884,7 +3884,7 @@ int rdbSaveToSlavesSockets(int req, rdbSaveInfo *rsi) {
     listIter li;
     pid_t childpid;
     int pipefds[2], rdb_pipe_write = 0, safe_to_exit_pipe = 0;
-    int rdb_channel = (req & SLAVE_REQ_RDB_CHANNEL);
+    int rdb_channel = server.repl_rdb_channel && (req & SLAVE_REQ_RDB_CHANNEL);
 
     if (hasActiveChildProcess()) return C_ERR;
 

src/replication.c

@@ -782,7 +782,7 @@ int replicationSetupSlaveForFullResync(client *slave, long long offset) {
     /* Don't send this reply to slaves that approached us with
      * the old SYNC command. */
     if (!(slave->flags & CLIENT_PRE_PSYNC)) {
-        if (slave->slave_req & SLAVE_REQ_RDB_CHANNEL) {
+        if (slave->flags & CLIENT_REPL_RDB_CHANNEL) {
             /* This slave is rdbchannel. Find its associated main channel and
              * change its state so we can deliver replication stream from now
              * on, in parallel to rdb. */
@@ -1356,8 +1356,16 @@ void replconfCommand(client *c) {
             if (getRangeLongFromObjectOrReply(c,c->argv[j+1],
                     0,1,&rdb_only,NULL) != C_OK)
                 return;
-            if (rdb_only == 1) c->flags |= CLIENT_REPL_RDBONLY;
-            else c->flags &= ~CLIENT_REPL_RDBONLY;
+            if (rdb_only == 1) {
+                c->flags |= CLIENT_REPL_RDBONLY;
+                /* If replicas ask for RDB only, We can apply the background
+                 * RDB transfer optimization based on the configurations. */
+                if (server.repl_rdb_channel && server.repl_diskless_sync)
+                    c->slave_req |= SLAVE_REQ_RDB_CHANNEL;
+            } else {
+                c->flags &= ~CLIENT_REPL_RDBONLY;
+                c->slave_req &= ~SLAVE_REQ_RDB_CHANNEL;
+            }
         } else if (!strcasecmp(c->argv[j]->ptr,"rdb-filter-only")) {
             /* REPLCONFG RDB-FILTER-ONLY is used to define "include" filters
              * for the RDB snapshot. Currently we only support a single
@@ -1391,10 +1399,8 @@ void replconfCommand(client *c) {
                 return;
             if (rdb_channel == 1) {
                 c->flags |= CLIENT_REPL_RDB_CHANNEL;
-                c->slave_req |= SLAVE_REQ_RDB_CHANNEL;
             } else {
                 c->flags &= ~CLIENT_REPL_RDB_CHANNEL;
-                c->slave_req &= ~SLAVE_REQ_RDB_CHANNEL;
             }
         } else if (!strcasecmp(c->argv[j]->ptr, "main-ch-client-id")) {
             /* REPLCONF main-ch-client-id <client-id> is used to identify

src/server.h

@@ -533,7 +533,7 @@ typedef enum {
 #define SLAVE_REQ_NONE                  0
 #define SLAVE_REQ_RDB_EXCLUDE_DATA      (1 << 0) /* Exclude data from RDB */
 #define SLAVE_REQ_RDB_EXCLUDE_FUNCTIONS (1 << 1) /* Exclude functions from RDB */
-#define SLAVE_REQ_RDB_CHANNEL           (1 << 2) /* Use rdb channel replication */
+#define SLAVE_REQ_RDB_CHANNEL           (1 << 2) /* Use rdb channel replication, transfer RDB background */
 /* Mask of all bits in the slave requirements bitfield that represent non-standard (filtered) RDB requirements */
 #define SLAVE_REQ_RDB_MASK (SLAVE_REQ_RDB_EXCLUDE_DATA | SLAVE_REQ_RDB_EXCLUDE_FUNCTIONS)
 

tests/integration/redis-cli.tcl

@@ -651,6 +651,9 @@ if {!$::tls} { ;# fake_redis_node doesn't support TLS
         r flushdb
         r function flush
 
+        if {!$::external} {
+            set lines [count_log_lines 0]
+        }
         set dir [lindex [r config get dir] 1]
 
         assert_equal "OK" [r debug populate 100000 key 1000]
@@ -663,6 +666,12 @@ if {!$::tls} { ;# fake_redis_node doesn't support TLS
         catch {run_cli {*}$args} output
         assert_match {*Transfer finished with success*} $output
 
+        # If server enabled diskless sync, it should transfer the RDB by RDB channel
+        # since server will automatically apply this optimization for rdb-only.
+        if {[r config get repl-diskless-sync] == "yes" && !$::external} {
+            verify_log_message 0 "*replicas sockets (rdb-channel)*" $lines
+        }
+
         file delete "$dir/dump.rdb"
         file rename "$dir/cli.rdb" "$dir/dump.rdb"