Cluster: clusterSetStartupEpoch() made more generally useful.

The actual goal of the function was to get the max configEpoch found in
the cluster, so make it general by removing the assignment of the max
epoch to currentEpoch that is useful only at startup.

src/cluster.c

@@ -73,21 +73,19 @@ void resetManualFailover(void);
  * Initialization
  * -------------------------------------------------------------------------- */
 
-/* This function is called at startup in order to set the currentEpoch
- * (which is not saved on permanent storage) to the greatest configEpoch found
- * in the loaded nodes (configEpoch is stored on permanent storage as soon as
- * it changes for some node). */
-void clusterSetStartupEpoch() {
+/* Return the greatest configEpoch found in the cluster. */
+uint64_t clusterGetMaxEpoch(void) {
+    uint64_t max = 0;
     dictIterator *di;
     dictEntry *de;
 
     di = dictGetSafeIterator(server.cluster->nodes);
     while((de = dictNext(di)) != NULL) {
         clusterNode *node = dictGetVal(de);
-        if (node->configEpoch > server.cluster->currentEpoch)
-            server.cluster->currentEpoch = node->configEpoch;
+        if (node->configEpoch > max) max = node->configEpoch;
     }
     dictReleaseIterator(di);
+    return max;
 }
 
 int clusterLoadConfig(char *filename) {
@@ -227,7 +225,10 @@ int clusterLoadConfig(char *filename) {
     /* Config sanity check */
     redisAssert(server.cluster->myself != NULL);
     redisLog(REDIS_NOTICE,"Node configuration loaded, I'm %.40s", myself->name);
-    clusterSetStartupEpoch();
+    /* Set the currentEpoch to the max epoch found in the master.
+     * FIXME: this should actually be part of the persistent state, as
+     * documented in the Github issue #1479. */
+    server.cluster->currentEpoch = clusterGetMaxEpoch();
     return REDIS_OK;
 
 fmterr: