Latency monitor trheshold value is now configurable.

This commit adds both support for redis.conf and CONFIG SET/GET.

redis.conf

@@ -562,6 +562,27 @@ slowlog-log-slower-than 10000
 # You can reclaim memory used by the slow log with SLOWLOG RESET.
 slowlog-max-len 128
 
+################################ LATENCY MONITOR ##############################
+
+# The Redis latency monitoring subsystem samples different operations
+# at runtime in order to collect data related to possible sources of
+# latency of a Redis instance.
+#
+# Via the LATENCY command this information is available to the user that can
+# print graphs and obtain reports.
+#
+# The system only logs operations that were performed in a time equal or
+# greater than the amount of milliseconds specified via the
+# latency-monitor-threshold configuration directive. When its value is set
+# to zero, the latency monitor is turned off.
+#
+# By default latency monitoring is disabled since it is mostly not needed
+# if you don't have latency issues, and collecting data has a performance
+# impact, that while very small, can be measured under big load. Latency
+# monitoring can easily be enalbed at runtime using the command
+# "CONFIG SET latency-monitor-threshold <milliseconds>" if needed.
+latency-monitor-threshold 0
+
 ############################# Event notification ##############################
 
 # Redis can notify Pub/Sub clients about events happening in the key space.

src/config.c

@@ -420,6 +420,14 @@ void loadServerConfigFromString(char *config) {
                    argc == 2)
         {
             server.slowlog_log_slower_than = strtoll(argv[1],NULL,10);
+        } else if (!strcasecmp(argv[0],"latency-monitor-threshold") &&
+                   argc == 2)
+        {
+            server.latency_monitor_threshold = strtoll(argv[1],NULL,10);
+            if (server.latency_monitor_threshold < 0) {
+                err = "The latency threshold can't be negative";
+                goto loaderr;
+            }
         } else if (!strcasecmp(argv[0],"slowlog-max-len") && argc == 2) {
             server.slowlog_max_len = strtoll(argv[1],NULL,10);
         } else if (!strcasecmp(argv[0],"client-output-buffer-limit") &&
@@ -747,6 +755,9 @@ void configSetCommand(redisClient *c) {
     } else if (!strcasecmp(c->argv[2]->ptr,"slowlog-max-len")) {
         if (getLongLongFromObject(o,&ll) == REDIS_ERR || ll < 0) goto badfmt;
         server.slowlog_max_len = (unsigned)ll;
+    } else if (!strcasecmp(c->argv[2]->ptr,"latency-monitor-threshold")) {
+        if (getLongLongFromObject(o,&ll) == REDIS_ERR || ll < 0) goto badfmt;
+        server.latency_monitor_threshold = ll;
     } else if (!strcasecmp(c->argv[2]->ptr,"loglevel")) {
         if (!strcasecmp(o->ptr,"warning")) {
             server.verbosity = REDIS_WARNING;
@@ -944,6 +955,8 @@ void configGetCommand(redisClient *c) {
     config_get_numerical_field("lua-time-limit",server.lua_time_limit);
     config_get_numerical_field("slowlog-log-slower-than",
             server.slowlog_log_slower_than);
+    config_get_numerical_field("latency-monitor-threshold",
+            server.latency_monitor_threshold);
     config_get_numerical_field("slowlog-max-len",
             server.slowlog_max_len);
     config_get_numerical_field("port",server.port);
@@ -1724,6 +1737,7 @@ int rewriteConfig(char *path) {
     rewriteConfigBytesOption(state,"auto-aof-rewrite-min-size",server.aof_rewrite_min_size,REDIS_AOF_REWRITE_MIN_SIZE);
     rewriteConfigNumericalOption(state,"lua-time-limit",server.lua_time_limit,REDIS_LUA_TIME_LIMIT);
     rewriteConfigNumericalOption(state,"slowlog-log-slower-than",server.slowlog_log_slower_than,REDIS_SLOWLOG_LOG_SLOWER_THAN);
+    rewriteConfigNumericalOption(state,"latency-monitor-threshold",server.latency_monitor_threshold,REDIS_DEFAULT_LATENCY_MONITOR_THRESHOLD);
     rewriteConfigNumericalOption(state,"slowlog-max-len",server.slowlog_max_len,REDIS_SLOWLOG_MAX_LEN);
     rewriteConfigNotifykeyspaceeventsOption(state);
     rewriteConfigNumericalOption(state,"hash-max-ziplist-entries",server.hash_max_ziplist_entries,REDIS_HASH_MAX_ZIPLIST_ENTRIES);