Optimize performance of clusterGenNodesDescription for large clusters (#8182)

Optimize the performance of clusterGenNodesDescription by only checking slot ownership of each slot once, instead of checking each slot for each node.

src/cluster.c

@@ -779,6 +779,7 @@ clusterNode *createClusterNode(char *nodename, int flags) {
     node->configEpoch = 0;
     node->flags = flags;
     memset(node->slots,0,sizeof(node->slots));
+    node->slots_info = NULL;
     node->numslots = 0;
     node->numslaves = 0;
     node->slaves = NULL;
@@ -4144,8 +4145,8 @@ sds clusterGenNodeDescription(clusterNode *node) {
     sds ci;
 
     /* Node coordinates */
-    ci = sdscatprintf(sdsempty(),"%.40s %s:%d@%d ",
-        node->name,
+    ci = sdscatlen(sdsempty(),node->name,CLUSTER_NAMELEN);
+    ci = sdscatfmt(ci," %s:%i@%i ",
         node->ip,
         node->port,
         node->cport);
@@ -4154,24 +4155,29 @@ sds clusterGenNodeDescription(clusterNode *node) {
     ci = representClusterNodeFlags(ci, node->flags);
 
     /* Slave of... or just "-" */
+    ci = sdscatlen(ci," ",1);
     if (node->slaveof)
-        ci = sdscatprintf(ci," %.40s ",node->slaveof->name);
+        ci = sdscatlen(ci,node->slaveof->name,CLUSTER_NAMELEN);
     else
-        ci = sdscatlen(ci," - ",3);
+        ci = sdscatlen(ci,"-",1);
 
     unsigned long long nodeEpoch = node->configEpoch;
     if (nodeIsSlave(node) && node->slaveof) {
         nodeEpoch = node->slaveof->configEpoch;
     }
     /* Latency from the POV of this node, config epoch, link status */
-    ci = sdscatprintf(ci,"%lld %lld %llu %s",
+    ci = sdscatfmt(ci," %I %I %U %s",
         (long long) node->ping_sent,
         (long long) node->pong_received,
         nodeEpoch,
         (node->link || node->flags & CLUSTER_NODE_MYSELF) ?
                     "connected" : "disconnected");
 
-    /* Slots served by this instance */
+    /* Slots served by this instance. If we already have slots info,
+     * append it diretly, otherwise, generate slots only if it has. */
+    if (node->slots_info) {
+        ci = sdscatsds(ci, node->slots_info);
+    } else if (node->numslots > 0) {
         start = -1;
         for (j = 0; j < CLUSTER_SLOTS; j++) {
             int bit;
@@ -4183,13 +4189,14 @@ sds clusterGenNodeDescription(clusterNode *node) {
                 if (bit && j == CLUSTER_SLOTS-1) j++;
 
                 if (start == j-1) {
-                ci = sdscatprintf(ci," %d",start);
+                    ci = sdscatfmt(ci," %i",start);
                 } else {
-                ci = sdscatprintf(ci," %d-%d",start,j-1);
+                    ci = sdscatfmt(ci," %i-%i",start,j-1);
                 }
                 start = -1;
             }
         }
+    }
 
     /* Just for MYSELF node we also dump info about slots that
      * we are migrating to other instances or importing from other
@@ -4208,6 +4215,41 @@ sds clusterGenNodeDescription(clusterNode *node) {
     return ci;
 }
 
+/* Generate the slot topology for all nodes and store the string representation
+ * in the slots_info struct on the node. This is used to improve the efficiency
+ * of clusterGenNodesDescription() because it removes looping of the slot space
+ * for generating the slot info for each node individually. */
+void clusterGenNodesSlotsInfo(int filter) {
+    clusterNode *n = NULL;
+    int start = -1;
+
+    for (int i = 0; i <= CLUSTER_SLOTS; i++) {
+        /* Find start node and slot id. */
+        if (n == NULL) {
+            if (i == CLUSTER_SLOTS) break;
+            n = server.cluster->slots[i];
+            start = i;
+            continue;
+        }
+
+        /* Generate slots info when occur different node with start
+         * or end of slot. */
+        if (i == CLUSTER_SLOTS || n != server.cluster->slots[i]) {
+            if (!(n->flags & filter)) {
+                if (n->slots_info == NULL) n->slots_info = sdsempty();
+                if (start == i-1) {
+                    n->slots_info = sdscatfmt(n->slots_info," %i",start);
+                } else {
+                    n->slots_info = sdscatfmt(n->slots_info," %i-%i",start,i-1);
+                }
+            }
+            if (i == CLUSTER_SLOTS) break;
+            n = server.cluster->slots[i];
+            start = i;
+        }
+    }
+}
+
 /* Generate a csv-alike representation of the nodes we are aware of,
  * including the "myself" node, and return an SDS string containing the
  * representation (it is up to the caller to free it).
@@ -4225,6 +4267,9 @@ sds clusterGenNodesDescription(int filter) {
     dictIterator *di;
     dictEntry *de;
 
+    /* Generate all nodes slots info firstly. */
+    clusterGenNodesSlotsInfo(filter);
+
     di = dictGetSafeIterator(server.cluster->nodes);
     while((de = dictNext(di)) != NULL) {
         clusterNode *node = dictGetVal(de);
@@ -4234,6 +4279,12 @@ sds clusterGenNodesDescription(int filter) {
         ci = sdscatsds(ci,ni);
         sdsfree(ni);
         ci = sdscatlen(ci,"\n",1);
+
+        /* Release slots info. */
+        if (node->slots_info) {
+            sdsfree(node->slots_info);
+            node->slots_info = NULL;
+        }
     }
     dictReleaseIterator(di);
     return ci;

src/cluster.h

@@ -118,6 +118,7 @@ typedef struct clusterNode {
     int flags;      /* CLUSTER_NODE_... */
     uint64_t configEpoch; /* Last configEpoch observed for this node */
     unsigned char slots[CLUSTER_SLOTS/8]; /* slots handled by this node */
+    sds slots_info; /* Slots info represented by string. */
     int numslots;   /* Number of slots handled by this node */
     int numslaves;  /* Number of slave nodes, if this is a master */
     struct clusterNode **slaves; /* pointers to slave nodes */

tests/cluster/tests/18-cluster-nodes-slots.tcl

@@ -0,0 +1,62 @@
+# Optimize CLUSTER NODES command by generating all nodes slot topology firstly
+
+source "../tests/includes/init-tests.tcl"
+
+proc cluster_allocate_with_continuous_slots {n} {
+    set slot 16383
+    set avg [expr ($slot+1) / $n]
+    while {$slot >= 0} {
+        set node [expr $slot/$avg >= $n ? $n-1 : $slot/$avg]
+        lappend slots_$node $slot
+        incr slot -1
+    }
+    for {set j 0} {$j < $n} {incr j} {
+        R $j cluster addslots {*}[set slots_${j}]
+    }
+}
+
+proc cluster_create_with_continuous_slots {masters slaves} {
+    cluster_allocate_with_continuous_slots $masters
+    if {$slaves} {
+        cluster_allocate_slaves $masters $slaves
+    }
+    assert_cluster_state ok
+}
+
+test "Create a 2 nodes cluster" {
+    cluster_create_with_continuous_slots 2 2
+}
+
+test "Cluster should start ok" {
+    assert_cluster_state ok
+}
+
+set master1 [Rn 0]
+set master2 [Rn 1]
+
+test "Continuous slots distribution" {
+    assert_match "* 0-8191*" [$master1 CLUSTER NODES]
+    assert_match "* 8192-16383*" [$master2 CLUSTER NODES]
+
+    $master1 CLUSTER DELSLOTS 4096
+    assert_match "* 0-4095 4097-8191*" [$master1 CLUSTER NODES]
+
+    $master2 CLUSTER DELSLOTS 12288
+    assert_match "* 8192-12287 12289-16383*" [$master2 CLUSTER NODES]
+}
+
+test "Discontinuous slots distribution" {
+    # Remove middle slots
+    $master1 CLUSTER DELSLOTS 4092 4094
+    assert_match "* 0-4091 4093 4095 4097-8191*" [$master1 CLUSTER NODES]
+    $master2 CLUSTER DELSLOTS 12284 12286
+    assert_match "* 8192-12283 12285 12287 12289-16383*" [$master2 CLUSTER NODES]
+
+    # Remove head slots
+    $master1 CLUSTER DELSLOTS 0 2
+    assert_match "* 1 3-4091 4093 4095 4097-8191*" [$master1 CLUSTER NODES]
+
+    # Remove tail slots
+    $master2 CLUSTER DELSLOTS 16380 16382 16383
+    assert_match "* 8192-12283 12285 12287 12289-16379 16381*" [$master2 CLUSTER NODES]
+}