Replicate slot migration states via RDB aux fields (#586)

.gitignore

@@ -45,4 +45,5 @@ redis.code-workspace
 .cache
 .cscope*
 .swp
+nodes.conf
 tests/cluster/tmp/*

src/cluster.h

@@ -103,7 +103,6 @@ char *clusterNodeHostname(clusterNode *node);
 const char *clusterNodePreferredEndpoint(clusterNode *n);
 long long clusterNodeReplOffset(clusterNode *node);
 clusterNode *clusterLookupNode(const char *name, int length);
-void clusterReplicateOpenSlots(void);
 int detectAndUpdateCachedNodeHealth(void);
 client *createCachedResponseClient(void);
 void deleteCachedResponseClient(client *recording_client);

src/cluster_legacy.c

@@ -113,6 +113,8 @@ int auxTlsPortPresent(clusterNode *n);
 static void clusterBuildMessageHdr(clusterMsg *hdr, int type, size_t msglen);
 void freeClusterLink(clusterLink *link);
 int verifyClusterNodeId(const char *name, int length);
+sds clusterEncodeOpenSlotsAuxField(int rdbflags);
+int clusterDecodeOpenSlotsAuxField(int rdbflags, sds s);
 
 int getNodeDefaultClientPort(clusterNode *n) {
     return server.tls_cluster ? n->tls_port : n->tcp_port;
@@ -1014,6 +1016,10 @@ void clusterInit(void) {
         exit(1);
     }
 
+    /* Register our own rdb aux fields */
+    serverAssert(rdbRegisterAuxField("cluster-slot-states", clusterEncodeOpenSlotsAuxField,
+                                     clusterDecodeOpenSlotsAuxField) == C_OK);
+
     /* Set myself->port/cport/pport to my listening ports, we'll just need to
      * discover the IP address via MEET messages. */
     deriveAnnouncedPorts(&myself->tcp_port, &myself->tls_port, &myself->cport);
@@ -6523,39 +6529,82 @@ int detectAndUpdateCachedNodeHealth(void) {
     return overall_health_changed;
 }
 
-/* Replicate migrating and importing slot states to all replicas */
-void clusterReplicateOpenSlots(void) {
-    if (!server.cluster_enabled) return;
+/* Encode open slot states into an sds string to be persisted as an aux field in RDB. */
+sds clusterEncodeOpenSlotsAuxField(int rdbflags) {
+    if (!server.cluster_enabled) return NULL;
 
-    int argc = 5;
-    robj **argv = zmalloc(sizeof(robj *) * argc);
+    /* Open slots should not be persisted to an RDB file. This data is intended only for full sync. */
+    if ((rdbflags & RDBFLAGS_REPLICATION) == 0) return NULL;
 
-    argv[0] = shared.cluster;
-    argv[1] = shared.setslot;
+    sds s = NULL;
 
     for (int i = 0; i < 2; i++) {
-        clusterNode **nodes_ptr = NULL;
+        clusterNode **nodes_ptr;
         if (i == 0) {
             nodes_ptr = server.cluster->importing_slots_from;
-            argv[3] = shared.importing;
         } else {
             nodes_ptr = server.cluster->migrating_slots_to;
-            argv[3] = shared.migrating;
         }
 
         for (int j = 0; j < CLUSTER_SLOTS; j++) {
             if (nodes_ptr[j] == NULL) continue;
-
-            argv[2] = createStringObjectFromLongLongForValue(j);
-            sds name = sdsnewlen(nodes_ptr[j]->name, sizeof(nodes_ptr[j]->name));
-            argv[4] = createObject(OBJ_STRING, name);
-
-            replicationFeedReplicas(0, argv, argc);
-
-            decrRefCount(argv[2]);
-            decrRefCount(argv[4]);
+            if (s == NULL) s = sdsempty();
+            s = sdscatfmt(s, "%i%s", j, (i == 0) ? "<" : ">");
+            s = sdscatlen(s, nodes_ptr[j]->name, CLUSTER_NAMELEN);
+            s = sdscatlen(s, ",", 1);
         }
     }
 
-    zfree(argv);
+    return s;
+}
+
+/* Decode the open slot aux field and restore the in-memory slot states. */
+int clusterDecodeOpenSlotsAuxField(int rdbflags, sds s) {
+    if (!server.cluster_enabled || s == NULL) return C_OK;
+
+    /* Open slots should not be loaded from a persisted RDB file, but only from a full sync. */
+    if ((rdbflags & RDBFLAGS_REPLICATION) == 0) return C_OK;
+
+    while (*s) {
+        /* Extract slot number */
+        int slot = atoi(s);
+        if (slot < 0 || slot >= CLUSTER_SLOTS) return C_ERR;
+
+        while (*s && *s != '<' && *s != '>') s++;
+        if (*s != '<' && *s != '>') return C_ERR;
+
+        /* Determine if it's an importing or migrating slot */
+        int is_importing = (*s == '<');
+        s++;
+
+        /* Extract the node name */
+        char node_name[CLUSTER_NAMELEN];
+        int k = 0;
+        while (*s && *s != ',' && k < CLUSTER_NAMELEN) {
+            node_name[k++] = *s++;
+        }
+
+        /* Ensure the node name is of the correct length */
+        if (k != CLUSTER_NAMELEN || *s != ',') return C_ERR;
+
+        /* Move to the next slot */
+        s++;
+
+        /* Find the corresponding node */
+        clusterNode *node = clusterLookupNode(node_name, CLUSTER_NAMELEN);
+        if (!node) {
+            /* Create a new node if not found */
+            node = createClusterNode(node_name, 0);
+            clusterAddNode(node);
+        }
+
+        /* Set the slot state */
+        if (is_importing) {
+            server.cluster->importing_slots_from[slot] = node;
+        } else {
+            server.cluster->migrating_slots_to[slot] = node;
+        }
+    }
+
+    return C_OK;
 }

src/latency.c

@@ -46,8 +46,6 @@ uint64_t dictStringHash(const void *key) {
     return dictGenHashFunction(key, strlen(key));
 }
 
-void dictVanillaFree(dict *d, void *val);
-
 dictType latencyTimeSeriesDictType = {
     dictStringHash,       /* hash function */
     NULL,                 /* key dup */

src/rdb.c

@@ -36,6 +36,7 @@
 #include "functions.h"
 #include "intset.h" /* Compact integer set structure */
 #include "bio.h"
+#include "zmalloc.h"
 
 #include <math.h>
 #include <fcntl.h>
@@ -107,6 +108,30 @@ void rdbReportError(int corruption_error, int linenum, char *reason, ...) {
     exit(1);
 }
 
+typedef struct {
+    rdbAuxFieldEncoder encoder;
+    rdbAuxFieldDecoder decoder;
+} rdbAuxFieldCodec;
+
+dictType rdbAuxFieldDictType = {
+    dictSdsCaseHash,       /* hash function */
+    NULL,                  /* key dup */
+    dictSdsKeyCaseCompare, /* key compare */
+    dictSdsDestructor,     /* key destructor */
+    dictVanillaFree,       /* val destructor */
+    NULL                   /* allow to expand */
+};
+
+dict *rdbAuxFields = NULL;
+
+int rdbRegisterAuxField(char *auxfield, rdbAuxFieldEncoder encoder, rdbAuxFieldDecoder decoder) {
+    if (rdbAuxFields == NULL) rdbAuxFields = dictCreate(&rdbAuxFieldDictType);
+    rdbAuxFieldCodec *codec = zmalloc(sizeof(rdbAuxFieldCodec));
+    codec->encoder = encoder;
+    codec->decoder = decoder;
+    return dictAdd(rdbAuxFields, sdsnew(auxfield), (void *)codec) == DICT_OK ? C_OK : C_ERR;
+}
+
 ssize_t rdbWriteRaw(rio *rdb, void *p, size_t len) {
     if (rdb && rioWrite(rdb, p, len) == 0) return -1;
     return len;
@@ -1186,6 +1211,24 @@ int rdbSaveInfoAuxFields(rio *rdb, int rdbflags, rdbSaveInfo *rsi) {
         if (rdbSaveAuxFieldStrInt(rdb, "repl-offset", server.primary_repl_offset) == -1) return -1;
     }
     if (rdbSaveAuxFieldStrInt(rdb, "aof-base", aof_base) == -1) return -1;
+
+    /* Handle additional dynamic aux fields */
+    if (rdbAuxFields != NULL) {
+        dictIterator di;
+        dictInitIterator(&di, rdbAuxFields);
+        dictEntry *de;
+        while ((de = dictNext(&di)) != NULL) {
+            rdbAuxFieldCodec *codec = (rdbAuxFieldCodec *)dictGetVal(de);
+            sds s = codec->encoder(rdbflags);
+            if (s == NULL) continue;
+            if (rdbSaveAuxFieldStrStr(rdb, dictGetKey(de), s) == -1) {
+                sdsfree(s);
+                return -1;
+            }
+            sdsfree(s);
+        }
+    }
+
     return 1;
 }
 
@@ -3099,9 +3142,22 @@ int rdbLoadRioWithLoadingCtx(rio *rdb, int rdbflags, rdbSaveInfo *rsi, rdbLoadin
             } else if (!strcasecmp(auxkey->ptr, "redis-bits")) {
                 /* Just ignored. */
             } else {
-                /* We ignore fields we don't understand, as by AUX field
-                 * contract. */
-                serverLog(LL_DEBUG, "Unrecognized RDB AUX field: '%s'", (char *)auxkey->ptr);
+                /* Check if this is a dynamic aux field */
+                int handled = 0;
+                if (rdbAuxFields != NULL) {
+                    dictEntry *de = dictFind(rdbAuxFields, auxkey->ptr);
+                    if (de != NULL) {
+                        handled = 1;
+                        rdbAuxFieldCodec *codec = (rdbAuxFieldCodec *)dictGetVal(de);
+                        if (codec->decoder(rdbflags, auxval->ptr) < 0) goto eoferr;
+                    }
+                }
+
+                if (!handled) {
+                    /* We ignore fields we don't understand, as by AUX field
+                     * contract. */
+                    serverLog(LL_DEBUG, "Unrecognized RDB AUX field: '%s'", (char *)auxkey->ptr);
+                }
             }
 
             decrRefCount(auxkey);

src/replication.c

@@ -1273,8 +1273,6 @@ int replicaPutOnline(client *replica) {
     moduleFireServerEvent(VALKEYMODULE_EVENT_REPLICA_CHANGE, VALKEYMODULE_SUBEVENT_REPLICA_CHANGE_ONLINE, NULL);
     serverLog(LL_NOTICE, "Synchronization with replica %s succeeded", replicationGetReplicaName(replica));
 
-    /* Replicate slot being migrated/imported to the new replica */
-    clusterReplicateOpenSlots();
     return 1;
 }
 

src/server.c

@@ -1914,10 +1914,6 @@ void createSharedObjects(void) {
     shared.special_asterick = createStringObject("*", 1);
     shared.special_equals = createStringObject("=", 1);
     shared.redacted = makeObjectShared(createStringObject("(redacted)", 10));
-    shared.cluster = createStringObject("CLUSTER", 7);
-    shared.setslot = createStringObject("SETSLOT", 7);
-    shared.importing = createStringObject("IMPORTING", 9);
-    shared.migrating = createStringObject("MIGRATING", 9);
 
     for (j = 0; j < OBJ_SHARED_INTEGERS; j++) {
         shared.integers[j] = makeObjectShared(createObject(OBJ_STRING, (void *)(long)j));

src/server.h

@@ -1032,6 +1032,9 @@ typedef struct rdbLoadingCtx {
     functionsLibCtx *functions_lib_ctx;
 } rdbLoadingCtx;
 
+typedef sds (*rdbAuxFieldEncoder)(int flags);
+typedef int (*rdbAuxFieldDecoder)(int flags, sds s);
+
 /* Client MULTI/EXEC state */
 typedef struct multiCmd {
     robj **argv;
@@ -1368,11 +1371,11 @@ struct sharedObjectsStruct {
         *xgroup, *xclaim, *script, *replconf, *eval, *persist, *set, *pexpireat, *pexpire, *time, *pxat, *absttl,
         *retrycount, *force, *justid, *entriesread, *lastid, *ping, *setid, *keepttl, *load, *createconsumer, *getack,
         *special_asterick, *special_equals, *default_username, *redacted, *ssubscribebulk, *sunsubscribebulk,
-        *smessagebulk, *cluster, *setslot, *importing, *migrating, *select[PROTO_SHARED_SELECT_CMDS],
-        *integers[OBJ_SHARED_INTEGERS], *mbulkhdr[OBJ_SHARED_BULKHDR_LEN], /* "*<value>\r\n" */
-        *bulkhdr[OBJ_SHARED_BULKHDR_LEN],                                  /* "$<value>\r\n" */
-        *maphdr[OBJ_SHARED_BULKHDR_LEN],                                   /* "%<value>\r\n" */
-        *sethdr[OBJ_SHARED_BULKHDR_LEN];                                   /* "~<value>\r\n" */
+        *smessagebulk, *select[PROTO_SHARED_SELECT_CMDS], *integers[OBJ_SHARED_INTEGERS],
+        *mbulkhdr[OBJ_SHARED_BULKHDR_LEN], /* "*<value>\r\n" */
+        *bulkhdr[OBJ_SHARED_BULKHDR_LEN],  /* "$<value>\r\n" */
+        *maphdr[OBJ_SHARED_BULKHDR_LEN],   /* "%<value>\r\n" */
+        *sethdr[OBJ_SHARED_BULKHDR_LEN];   /* "~<value>\r\n" */
     sds minstring, maxstring;
 };
 
@@ -2603,6 +2606,7 @@ int serverSetProcTitle(char *title);
 int validateProcTitleTemplate(const char *template);
 int serverCommunicateSystemd(const char *sd_notify_msg);
 void serverSetCpuAffinity(const char *cpulist);
+void dictVanillaFree(dict *d, void *val);
 
 /* afterErrorReply flags */
 #define ERR_REPLY_FLAG_NO_STATS_UPDATE                                                                                 \
@@ -2904,6 +2908,7 @@ void rebaseReplicationBuffer(long long base_repl_offset);
 void showLatestBacklog(void);
 void rdbPipeReadHandler(struct aeEventLoop *eventLoop, int fd, void *clientData, int mask);
 void rdbPipeWriteHandlerConnRemoved(struct connection *conn);
+int rdbRegisterAuxField(char *auxfield, rdbAuxFieldEncoder encoder, rdbAuxFieldDecoder decoder);
 void clearFailoverState(void);
 void updateFailoverStatus(void);
 void abortFailover(const char *err);

tests/support/cluster_util.tcl

@@ -371,3 +371,7 @@ proc check_cluster_node_mark {flag ref_node_index instance_id_to_check} {
     }
     fail "Unable to find instance id in cluster nodes. ID: $instance_id_to_check"
 }
+
+proc get_slot_field {slot_output shard_id node_id attrib_id} {
+    return [lindex [lindex [lindex $slot_output $shard_id] $node_id] $attrib_id]
+}

tests/unit/cluster/hostnames.tcl

@@ -1,7 +1,3 @@
-proc get_slot_field {slot_output shard_id node_id attrib_id} {
-    return [lindex [lindex [lindex $slot_output $shard_id] $node_id] $attrib_id]
-}
-
 # Start a cluster with 3 masters and 4 replicas.
 # These tests rely on specific node ordering, so make sure no node fails over.
 start_cluster 3 4 {tags {external:skip cluster} overrides {cluster-replica-no-failover yes}} {

tests/unit/cluster/slot-migration.tcl

@@ -15,9 +15,6 @@ proc get_cluster_role {srv_idx} {
 }
 
 proc wait_for_role {srv_idx role} {
-    set node_timeout [lindex [R 0 CONFIG GET cluster-node-timeout] 1]
-    # wait for a gossip cycle for states to be propagated throughout the cluster
-    after $node_timeout
     wait_for_condition 100 100 {
         [lindex [split [R $srv_idx ROLE] " "] 0] eq $role
     } else {
@@ -198,7 +195,7 @@ start_cluster 3 3 {tags {external:skip cluster} overrides {cluster-allow-replica
         assert_equal {OK} [R 3 CLUSTER REPLICATE $R0_id]
         wait_for_role 3 slave
         # Validate that R3 now sees slot 609 open
-        assert_equal [get_open_slots 3] "\[609->-$R1_id\]"
+        wait_for_slot_state 3 "\[609->-$R1_id\]"
     }
 
     test "New replica inherits importing slot" {
@@ -212,7 +209,7 @@ start_cluster 3 3 {tags {external:skip cluster} overrides {cluster-allow-replica
         assert_equal {OK} [R 4 CLUSTER REPLICATE $R1_id]
         wait_for_role 4 slave
         # Validate that R4 now sees slot 609 open
-        assert_equal [get_open_slots 4] "\[609-<-$R0_id\]"
+        wait_for_slot_state 4 "\[609-<-$R0_id\]"
     }
 }