Sentinel: Redis-side support for slave priority.

A Redis slave can now be configured with a priority, that is an integer
number that is shown in INFO output and can be get and set using the
redis.conf file or the CONFIG GET/SET command.

This field is used by Sentinel during slave election. A slave with lower
priority is preferred. A slave with priority zero is never elected (and
is considered to be impossible to elect even if it is the only slave
available).

A next commit will add support in the Sentinel side as well.

src/config.c

@@ -347,6 +347,8 @@ void loadServerConfigFromString(char *config) {
             if ((server.stop_writes_on_bgsave_err = yesnotoi(argv[1])) == -1) {
                 err = "argument must be 'yes' or 'no'"; goto loaderr;
             }
+        } else if (!strcasecmp(argv[0],"slave-priority") && argc == 2) {
+            server.slave_priority = atoi(argv[1]);
         } else {
             err = "Bad directive or wrong number of arguments"; goto loaderr;
         }
@@ -648,6 +650,10 @@ void configSetCommand(redisClient *c) {
 
         if (yn == -1) goto badfmt;
         server.rdb_checksum = yn;
+    } else if (!strcasecmp(c->argv[2]->ptr,"slave-priority")) {
+        if (getLongLongFromObject(o,&ll) == REDIS_ERR ||
+            ll <= 0) goto badfmt;
+        server.slave_priority = ll;
     } else {
         addReplyErrorFormat(c,"Unsupported CONFIG parameter: %s",
             (char*)c->argv[2]->ptr);
@@ -737,6 +743,7 @@ void configGetCommand(redisClient *c) {
     config_get_numerical_field("repl-timeout",server.repl_timeout);
     config_get_numerical_field("maxclients",server.maxclients);
     config_get_numerical_field("watchdog-period",server.watchdog_period);
+    config_get_numerical_field("slave-priority",server.slave_priority);
 
     /* Bool (yes/no) values */
     config_get_bool_field("no-appendfsync-on-rewrite",

src/redis.c

@@ -1137,6 +1137,7 @@ void initServerConfig() {
     server.repl_serve_stale_data = 1;
     server.repl_slave_ro = 1;
     server.repl_down_since = time(NULL);
+    server.slave_priority = REDIS_DEFAULT_SLAVE_PRIORITY;
 
     /* Client output buffer limits */
     server.client_obuf_limits[REDIS_CLIENT_LIMIT_CLASS_NORMAL].hard_limit_bytes = 0;
@@ -2045,6 +2046,8 @@ sds genRedisInfoString(char *section) {
                     "master_link_down_since_seconds:%ld\r\n",
                     (long)server.unixtime-server.repl_down_since);
             }
+            info = sdscatprintf(info,
+                "slave_priority:%d\r\n", server.slave_priority);
         }
         info = sdscatprintf(info,
             "connected_slaves:%lu\r\n",

src/redis.h

@@ -57,10 +57,9 @@
 #define REDIS_SLOWLOG_MAX_LEN 128
 #define REDIS_MAX_CLIENTS 10000
 #define REDIS_AUTHPASS_MAX_LEN 512
-
+#define REDIS_DEFAULT_SLAVE_PRIORITY 100
 #define REDIS_REPL_TIMEOUT 60
 #define REDIS_REPL_PING_SLAVE_PERIOD 10
-
 #define REDIS_RUN_ID_SIZE 40
 #define REDIS_OPS_SEC_SAMPLES 16
 
@@ -559,6 +558,7 @@ struct redisServer {
     int repl_serve_stale_data; /* Serve stale data when link is down? */
     int repl_slave_ro;          /* Slave is read only? */
     time_t repl_down_since; /* Unix time at which link with master went down */
+    int slave_priority;             /* Reported in INFO and used by Sentinel. */
     /* Limits */
     unsigned int maxclients;        /* Max number of simultaneous clients */
     unsigned long long maxmemory;   /* Max number of memory bytes to use */