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

@@ -333,6 +333,8 @@ void loadServerConfig(char *filename) {
             server.slowlog_log_slower_than = strtoll(argv[1],NULL,10);
         } else if (!strcasecmp(argv[0],"slowlog-max-len") && argc == 2) {
             server.slowlog_max_len = strtoll(argv[1],NULL,10);
+        } 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;
         }
@@ -531,6 +533,10 @@ void configSetCommand(redisClient *c) {
         } else {
             goto badfmt;
         }
+    } 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);
@@ -711,6 +717,11 @@ void configGetCommand(redisClient *c) {
         addReplyBulkLongLong(c,server.slowlog_max_len);
         matches++;
     }
+    if (stringmatch(pattern,"slave-priority",0)) {
+        addReplyBulkCString(c,"slave-priority");
+        addReplyBulkLongLong(c,server.slave_priority);
+        matches++;
+    }
     if (stringmatch(pattern,"loglevel",0)) {
         char *s;
 

src/redis.c

@@ -877,6 +877,7 @@ void initServerConfig() {
     server.repl_syncio_timeout = REDIS_REPL_SYNCIO_TIMEOUT;
     server.repl_serve_stale_data = 1;
     server.repl_down_since = time(NULL);
+    server.slave_priority = REDIS_DEFAULT_SLAVE_PRIORITY;
 
     /* Double constants initialization */
     R_Zero = 0.0;
@@ -1440,6 +1441,8 @@ sds genRedisInfoString(void) {
                 "master_link_down_since_seconds:%ld\r\n",
                 (long)time(NULL)-server.repl_down_since);
         }
+        info = sdscatprintf(info,
+            "slave_priority:%d\r\n", server.slave_priority);
     }
 
     if (server.vm_enabled) {

src/redis.h

@@ -62,6 +62,7 @@
 #define REDIS_REPL_PING_SLAVE_PERIOD 10
 
 #define REDIS_RUN_ID_SIZE 40
+#define REDIS_DEFAULT_SLAVE_PRIORITY 100
 
 /* Hash table parameters */
 #define REDIS_HT_MINFILL        10      /* Minimal hash table fill 10% */
@@ -479,6 +480,7 @@ struct redisServer {
     time_t repl_transfer_lastio; /* unix time of the latest read, for timeout */
     int repl_serve_stale_data; /* Serve stale data when link is down? */
     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;
     unsigned long long maxmemory;