TCP keep-alive. Better documentation in redis.conf.

redis.conf

@@ -41,13 +41,18 @@ timeout 0
 
 # TCP keepalive.
 #
-# When this option is set to a non-zero value, SO_KEEPALIVE option will be
-# enabled in order to send ACKs just to avoid connection drops or to detect
-# dead peers.
+# If non-zero, use SO_KEEPALIVE to send TCP ACKs to clients in absence
+# of communication. This is useful for two reasons:
 #
-# The value you specify with this option is the period (in seconds) we use
-# in order to refresh the connection with TCP ACKs, however the period is
-# only actually set on Linux. Other kernels will use the system-wide default.
+# 1) Detect dead peers.
+# 2) Take the connection alive from the point of view of network
+#    equipment in the middle.
+#
+# On Linux, the specified value (in seconds) is the period used to send ACKs.
+# Note that to close the connection the double of the time is needed.
+# On other kernels the period depends on the kernel configuration.
+#
+# A reasonable value for this option is 60 seconds.
 tcp-keepalive 0
 
 # Specify the server verbosity level.