Cluster: new option to work with partial slots coverage.

redis.conf

@@ -660,6 +660,19 @@ lua-time-limit 5000
 #
 # cluster-migration-barrier 1
 
+# By default Redis Cluster nodes stop accepting queries if they detect there
+# is at least an hash slot uncovered (no available node is serving it).
+# This way if the cluster is partially down (for example a range of hash slots
+# are no longer covered) all the cluster becomes, eventually, unavailable.
+# It automatically returns available as soon as all the slots are covered again.
+#
+# However sometimes you want the subset of the cluster which is working,
+# to continue to accept queries for the part of the key space that is still
+# covered. In order to do so, just set the cluster-require-full-coverage
+# option to no.
+#
+# cluster-require-full-coverage yes
+
 # In order to setup your cluster make sure to read the documentation
 # available at http://redis.io web site.
 

src/cluster.c

@@ -3171,12 +3171,14 @@ void clusterUpdateState(void) {
     new_state = REDIS_CLUSTER_OK;
 
     /* Check if all the slots are covered. */
-    for (j = 0; j < REDIS_CLUSTER_SLOTS; j++) {
-        if (server.cluster->slots[j] == NULL ||
-            server.cluster->slots[j]->flags & (REDIS_NODE_FAIL))
-        {
-            new_state = REDIS_CLUSTER_FAIL;
-            break;
+    if (server.cluster_require_full_coverage) {
+        for (j = 0; j < REDIS_CLUSTER_SLOTS; j++) {
+            if (server.cluster->slots[j] == NULL ||
+                server.cluster->slots[j]->flags & (REDIS_NODE_FAIL))
+            {
+                new_state = REDIS_CLUSTER_FAIL;
+                break;
+            }
         }
     }
 

src/cluster.h

@@ -15,6 +15,7 @@
  * multiplicators of the node timeout value (when ending with MULT). */
 #define REDIS_CLUSTER_DEFAULT_NODE_TIMEOUT 15000
 #define REDIS_CLUSTER_DEFAULT_SLAVE_VALIDITY 10 /* Slave max data age factor. */
+#define REDIS_CLUSTER_DEFAULT_REQUIRE_FULL_COVERAGE 1
 #define REDIS_CLUSTER_FAIL_REPORT_VALIDITY_MULT 2 /* Fail report validity. */
 #define REDIS_CLUSTER_FAIL_UNDO_TIME_MULT 2 /* Undo fail if master is back. */
 #define REDIS_CLUSTER_FAIL_UNDO_TIME_ADD 10 /* Some additional time. */

src/config.c

@@ -429,6 +429,13 @@ void loadServerConfigFromString(char *config) {
         } else if (!strcasecmp(argv[0],"cluster-config-file") && argc == 2) {
             zfree(server.cluster_configfile);
             server.cluster_configfile = zstrdup(argv[1]);
+        } else if (!strcasecmp(argv[0],"cluster-require-full-coverage") &&
+                    argc == 2)
+        {
+            if ((server.cluster_require_full_coverage = yesnotoi(argv[1])) == -1)
+            {
+                err = "argument must be 'yes' or 'no'"; goto loaderr;
+            }
         } else if (!strcasecmp(argv[0],"cluster-node-timeout") && argc == 2) {
             server.cluster_node_timeout = strtoll(argv[1],NULL,10);
             if (server.cluster_node_timeout <= 0) {
@@ -918,6 +925,11 @@ void configSetCommand(redisClient *c) {
             ll < 0) goto badfmt;
         server.repl_min_slaves_max_lag = ll;
         refreshGoodSlavesCount();
+    } else if (!strcasecmp(c->argv[2]->ptr,"cluster-require-full-coverage")) {
+        int yn = yesnotoi(o->ptr);
+
+        if (yn == -1) goto badfmt;
+        server.cluster_require_full_coverage = yn;
     } else if (!strcasecmp(c->argv[2]->ptr,"cluster-node-timeout")) {
         if (getLongLongFromObject(o,&ll) == REDIS_ERR ||
             ll <= 0) goto badfmt;
@@ -1039,6 +1051,8 @@ void configGetCommand(redisClient *c) {
     config_get_numerical_field("cluster-slave-validity-factor",server.cluster_slave_validity_factor);
 
     /* Bool (yes/no) values */
+    config_get_bool_field("cluster-require-full-coverage",
+            server.cluster_require_full_coverage);
     config_get_bool_field("no-appendfsync-on-rewrite",
             server.aof_no_fsync_on_rewrite);
     config_get_bool_field("slave-serve-stale-data",
@@ -1806,6 +1820,7 @@ int rewriteConfig(char *path) {
     rewriteConfigNumericalOption(state,"lua-time-limit",server.lua_time_limit,REDIS_LUA_TIME_LIMIT);
     rewriteConfigYesNoOption(state,"cluster-enabled",server.cluster_enabled,0);
     rewriteConfigStringOption(state,"cluster-config-file",server.cluster_configfile,REDIS_DEFAULT_CLUSTER_CONFIG_FILE);
+    rewriteConfigYesNoOption(state,"cluster-require-full-coverage",server.cluster_require_full_coverage,REDIS_CLUSTER_DEFAULT_REQUIRE_FULL_COVERAGE);
     rewriteConfigNumericalOption(state,"cluster-node-timeout",server.cluster_node_timeout,REDIS_CLUSTER_DEFAULT_NODE_TIMEOUT);
     rewriteConfigNumericalOption(state,"cluster-migration-barrier",server.cluster_migration_barrier,REDIS_CLUSTER_DEFAULT_MIGRATION_BARRIER);
     rewriteConfigNumericalOption(state,"cluster-slave-validity-factor",server.cluster_slave_validity_factor,REDIS_CLUSTER_DEFAULT_SLAVE_VALIDITY);

src/redis.c

@@ -1451,6 +1451,7 @@ void initServerConfig(void) {
     server.cluster_node_timeout = REDIS_CLUSTER_DEFAULT_NODE_TIMEOUT;
     server.cluster_migration_barrier = REDIS_CLUSTER_DEFAULT_MIGRATION_BARRIER;
     server.cluster_slave_validity_factor = REDIS_CLUSTER_DEFAULT_SLAVE_VALIDITY;
+    server.cluster_require_full_coverage = REDIS_CLUSTER_DEFAULT_REQUIRE_FULL_COVERAGE;
     server.cluster_configfile = zstrdup(REDIS_DEFAULT_CLUSTER_CONFIG_FILE);
     server.lua_caller = NULL;
     server.lua_time_limit = REDIS_LUA_TIME_LIMIT;

src/redis.h

@@ -858,6 +858,8 @@ struct redisServer {
     struct clusterState *cluster;  /* State of the cluster */
     int cluster_migration_barrier; /* Cluster replicas migration barrier. */
     int cluster_slave_validity_factor; /* Slave max data age for failover. */
+    int cluster_require_full_coverage; /* If true, put the cluster down if
+                                          there is at least an uncovered slot. */
     /* Scripting */
     lua_State *lua; /* The Lua interpreter. We use just one for all clients */
     redisClient *lua_client;   /* The "fake client" to query Redis from Lua */