Warn when configured maxmemory value seems odd.

This commit warns the user with a log at "warning" level if:

1) After the server startup the maxmemory limit was found to be < 1MB.
2) After a CONFIG SET command modifying the maxmemory setting the limit
is set to a value that is smaller than the currently used memory.

The behaviour of the Redis server is unmodified, and this wil not make
the CONFIG SET command or a wrong configuration in redis.conf less
likely to create problems, but at least this will make aware most users
about a possbile error they committed without resorting to external
help.

However no warning is issued if, as a result of loading the AOF or RDB
file, we are very near the maxmemory setting, or key eviction will be
needed in order to go under the specified maxmemory setting. The reason
is that in servers configured as a cache with an aggressive
maxmemory-policy most of the times restarting the server will cause this
condition to happen if persistence is not switched off.

This fixes issue #429.

diff --git a/src/config.c b/src/config.c
index 768db1e9ab9229d8567b52b42d5ee3a3a2651c95..a36eb9a392b0ffcbd1cdfac502409d9e7e024e4f 100644 (file)
--- a/src/config.c
+++ b/src/config.c
@@ -438,7 +438,12 @@ void configSetCommand(redisClient *c) {
         if (getLongLongFromObject(o,&ll) == REDIS_ERR ||
             ll < 0) goto badfmt;
         server.maxmemory = ll;
-        if (server.maxmemory) freeMemoryIfNeeded();
+        if (server.maxmemory) {
+            if (server.maxmemory < zmalloc_used_memory()) {
+                redisLog(REDIS_WARNING,"WARNING: the new maxmemory value set via CONFIG SET is smaller than the current memory usage. This will result in keys eviction and/or inability to accept new write commands depending on the maxmemory-policy.");
+            }
+            freeMemoryIfNeeded();
+        }
     } else if (!strcasecmp(c->argv[2]->ptr,"maxmemory-policy")) {
         if (!strcasecmp(o->ptr,"volatile-lru")) {
             server.maxmemory_policy = REDIS_MAXMEMORY_VOLATILE_LRU;

diff --git a/src/redis.c b/src/redis.c
index 0656d7c294bfaace069c7f8947f40ecad30491dd..aa5a73f2abae195632463461416acf60c5c3f887 100644 (file)
--- a/src/redis.c
+++ b/src/redis.c
@@ -2578,6 +2578,11 @@ int main(int argc, char **argv) {
             redisLog(REDIS_NOTICE,"The server is now ready to accept connections at %s", server.unixsocket);
     }
 
+    /* Warning the user about suspicious maxmemory setting. */
+    if (server.maxmemory > 0 && server.maxmemory < 1024*1024) {
+        redisLog(REDIS_WARNING,"WARNING: You specified a maxmemory value that is less than 1MB (current value is %llu bytes). Are you sure this is what you really want?", server.maxmemory);
+    }
+
     aeSetBeforeSleepProc(server.el,beforeSleep);
     aeMain(server.el);
     aeDeleteEventLoop(server.el);