maxclients configuration is now implemented dealing with the actual process rlimits. Setting maxclients to 0 no longer makes sense and is now invalid, the new default is 10000.

See issue #162 for more information.

redis.conf

@@ -168,13 +168,16 @@ slave-serve-stale-data yes
 
 ################################### LIMITS ####################################
 
-# Set the max number of connected clients at the same time. By default there
-# is no limit, and it's up to the number of file descriptors the Redis process
-# is able to open. The special value '0' means no limits.
+# Set the max number of connected clients at the same time. By default
+# this limit is set to 10000 clients, however if the Redis server is not
+# able ot configure the process file limit to allow for the specified limit
+# the max number of allowed clients is set to the current file limit
+# minus 32 (as Redis reserves a few file descriptors for internal uses).
+#
 # Once the limit is reached Redis will close all the new connections sending
 # an error 'max number of clients reached'.
 #
-# maxclients 128
+# maxclients 10000
 
 # Don't use more memory than the specified amount of bytes.
 # When the memory limit is reached Redis will try to remove keys with an

src/networking.c

@@ -412,7 +412,7 @@ static void acceptCommonHandler(int fd) {
      * connection. Note that we create the client instead to check before
      * for this condition, since now the socket is already set in nonblocking
      * mode and we can send an error for free using the Kernel I/O */
-    if (server.maxclients && listLength(server.clients) > server.maxclients) {
+    if (listLength(server.clients) > server.maxclients) {
         char *err = "-ERR max number of clients reached\r\n";
 
         /* That's a best effort error message, don't check write errors */

src/redis.c

@@ -856,7 +856,7 @@ void initServerConfig() {
     server.requirepass = NULL;
     server.rdbcompression = 1;
     server.activerehashing = 1;
-    server.maxclients = 0;
+    server.maxclients = REDIS_MAX_CLIENTS;
     server.bpop_blocked_clients = 0;
     server.maxmemory = 0;
     server.maxmemory_policy = REDIS_MAXMEMORY_VOLATILE_LRU;
@@ -1000,6 +1000,39 @@ void initServer() {
     slowlogInit();
     bioInit();
     srand(time(NULL)^getpid());
+
+    /* Try to raise the max number of open files accordingly to the
+     * configured max number of clients. Also account for 32 additional
+     * file descriptors as we need a few more for persistence, listening
+     * sockets, log files and so forth. */
+    {
+        rlim_t maxfiles = server.maxclients+32;
+        struct rlimit limit;
+
+        if (maxfiles < 1024) maxfiles = 1024;
+        if (getrlimit(RLIMIT_NOFILE,&limit) == -1) {
+            redisLog(REDIS_WARNING,"Unable to obtain the current NOFILE limit (%s), assuming 1024 and setting the max clients configuration accordingly.",
+                strerror(errno));
+            server.maxclients = 1024-32;
+        } else {
+            rlim_t oldlimit = limit.rlim_cur;
+
+            /* Set the max number of files if the current limit is not enough
+             * for our needs. */
+            if (oldlimit < maxfiles) {
+                limit.rlim_cur = maxfiles;
+                limit.rlim_max = maxfiles;
+                if (setrlimit(RLIMIT_NOFILE,&limit) == -1) {
+                    server.maxclients = oldlimit-32;
+                    redisLog(REDIS_WARNING,"Unable to set the max number of files limit to %d (%s), setting the max clients configuration to %d.",
+                        (int) maxfiles, strerror(errno), (int) server.maxclients);
+                } else {
+                    redisLog(REDIS_NOTICE,"Max number of open files set to %d",
+                        (int) maxfiles);
+                }
+            }
+        }
+    }
 }
 
 /* Populates the Redis Command Table starting from the hard coded list

src/redis.h

@@ -55,6 +55,7 @@
 #define REDIS_AUTO_AOFREWRITE_MIN_SIZE (1024*1024)
 #define REDIS_SLOWLOG_LOG_SLOWER_THAN 10000
 #define REDIS_SLOWLOG_MAX_LEN 64
+#define REDIS_MAX_CLIENTS 10000
 
 /* Hash table parameters */
 #define REDIS_HT_MINFILL        10      /* Minimal hash table fill 10% */