add flushdb option for repl-diskless-load

src/config.c

@@ -87,6 +87,7 @@ configEnum shutdown_on_sig_enum[] = {{"default", 0},        {"save", SHUTDOWN_SA
 configEnum repl_diskless_load_enum[] = {{"disabled", REPL_DISKLESS_LOAD_DISABLED},
                                         {"on-empty-db", REPL_DISKLESS_LOAD_WHEN_DB_EMPTY},
                                         {"swapdb", REPL_DISKLESS_LOAD_SWAPDB},
+                                        {"flushdb", REPL_DISKLESS_LOAD_FLUSHDB},
                                         {NULL, 0}};
 
 configEnum tls_auth_clients_enum[] = {{"no", TLS_CLIENT_AUTH_NO},

src/replication.c

@@ -1943,6 +1943,7 @@ void restartAOFAfterSYNC(void) {
 static int useDisklessLoad(void) {
     /* compute boolean decision to use diskless load */
     int enabled = server.repl_diskless_load == REPL_DISKLESS_LOAD_SWAPDB ||
+                  server.repl_diskless_load == REPL_DISKLESS_LOAD_FLUSHDB ||
                   (server.repl_diskless_load == REPL_DISKLESS_LOAD_WHEN_DB_EMPTY && dbTotalServerKeyCount() == 0);
 
     if (enabled) {

src/server.h

@@ -504,6 +504,7 @@ typedef enum {
 #define REPL_DISKLESS_LOAD_DISABLED 0
 #define REPL_DISKLESS_LOAD_WHEN_DB_EMPTY 1
 #define REPL_DISKLESS_LOAD_SWAPDB 2
+#define REPL_DISKLESS_LOAD_FLUSHDB 3
 
 /* TLS Client Authentication */
 #define TLS_CLIENT_AUTH_NO 0

tests/integration/replication.tcl

@@ -1478,6 +1478,63 @@ start_server {tags {"repl external:skip"}} {
     }
 }
 
+foreach dualchannel {yes no} {
+    test "replica actually flushes db if use diskless load with flushdb dual-channel-replication-enabled=$dualchannel" {
+        start_server {tags {"repl"}} {
+            set replica [srv 0 client]
+            set replica_log [srv 0 stdout]
+            start_server {} {
+                set master [srv 0 client]
+                set master_host [srv 0 host]
+                set master_port [srv 0 port]
+
+                # Fill both replica and master with data
+                $master debug populate 100 master 100000
+                $replica debug populate 201 replica 100000
+                assert_equal [$replica dbsize] 201
+                # Set up master
+                $master config set save ""
+                $master config set rdbcompression no
+                $master config set repl-diskless-sync yes
+                $master config set repl-diskless-sync-delay 0
+                $master config set dual-channel-replication-enabled $dualchannel
+                # Set master with a slow rdb generation, so that we can easily intercept loading
+                # 10ms per key, with 1000 keys is 10 seconds
+                $master config set rdb-key-save-delay 10000
+                # Set up replica
+                $replica config set save ""
+                $replica config set repl-diskless-load flushdb
+                $replica config set dual-channel-replication-enabled $dualchannel
+                # Start the replication process...
+                $replica replicaof $master_host $master_port
+
+                wait_for_condition 100 100 {
+                    [s -1 loading] eq 1
+                } else {
+                    fail "Replica didn't start loading"
+                }
+
+                # Make sure that next sync will not start immediately so that we can catch the replica in between syncs
+                $master config set repl-diskless-sync-delay 5
+
+                # Kill the replica connection on the master
+                set killed [$master client kill type replica]
+
+                wait_for_condition 100 100 {
+                    [s -1 loading] eq 0
+                } else {
+                    fail "Replica didn't disconnect"
+                }
+
+                assert_equal [$replica dbsize] 0
+
+                # Speed up shutdown
+                $master config set rdb-key-save-delay 0
+            }
+        }
+    } {} {external:skip}
+}
+
 start_server {tags {"repl external:skip"}} {
     set replica [srv 0 client]
     $replica set replica_key replica_value

valkey.conf

@@ -678,6 +678,9 @@ repl-diskless-sync-max-replicas 0
 # "on-empty-db" - Use diskless load only when current dataset is empty. This is 
 #                 safer and avoid having old and new dataset loaded side by side
 #                 during replication.
+# "flushdb"     - Flush the current db contents before parsing. Note that if
+#                 there's a problem before the replication succeeded you may
+#                 lose all your data.
 repl-diskless-load disabled
 
 # This dual channel replication sync feature optimizes the full synchronization process