浅谈redis的maxmemory设置以及淘汰策略

The issue happens for the following reason:
 
Redis reached the configured limit, so it tries to expire keys.
Evicting keys turns into explicit DELs sent to slaves, since masters control the eviction of slaves for well known reasons.
But this way if there are enough slaves, emitting the protocol in the output buffers will actually take more memory than the amount freed removing keys...
So the key eviction process starts to enter into an infinite loop.
Up to a given point the fact that there is a static buffer part in the output queue of every client (including slaves) mitigate this in certain conditions, but once Redis can't use the output buffer but must use the queue of objects the infinite loop is triggered. 

# WARNING: If you have slaves attached to an instance with maxmemory on,
# the size of the output buffers needed to feed the slaves are subtracted
# from the used memory count, so that network problems / resyncs will
# not trigger a loop where keys are evicted, and in turn the output
# buffer of slaves is full with DELs of keys evicted triggering the deletion
# of more keys, and so forth until the database is completely emptied.
#
# In short... if you have slaves attached it is suggested that you set a lower
# limit for maxmemory so that there is some free RAM on the system for slave
# output buffers (but this is not needed if the policy is 'noeviction').
#
# maxmemory <bytes></bytes>