Redis基础知识（学习笔记19--Redis Sentinel）

# sentinel down-after-milliseconds <master-name> <milliseconds>
#
# Number of milliseconds the master (or any attached【所依附的】 slave or sentinel) should
# be unreachable (as in, not acceptable reply to PING, continuously, for the
# specified period) in order to consider it in S_DOWN state (Subjectively
# Down).
# 这段的意思是sentinel在和master【注意：不仅仅是master，还有slave、sentinel】失联多少毫秒后，可以做出主节点S_DOWN的判断。
# 此参数的作用范围不仅仅是 sentinel到master的连接；还有sentinel到slave的连接；sentinel到sentinel的连接。
# Default is 30 seconds.

sentinel down-after-milliseconds mymaster 30000

# sentinel parallel-syncs <master-name> <numslaves>
#
# How many slaves we can reconfigure to point to the new slave simultaneously【同时】
# during the failover. Use a low number if you use the slaves to serve query
# to avoid that all the slaves will be unreachable at about the same
# time while performing the synchronization with the master.
##如果想在failover期间，slave同步新master的这个过程中，仍然想有部分slave 可以提供查询服务，那么可以将这个
##值设置小一点。【需要注意的是，这样带来的坏处就是：提供的查询服务，不保证数据的一致性，和主节点是有数据差异的；
##此外，faiover的master 和 所有slave的数据同步过程被拉长了】
sentinel parallel-syncs mymaster 1

# sentinel failover-timeout <master-name> <milliseconds>
#
# Specifies the failover timeout in milliseconds. It is used in many ways: ##【注意：这个时间有多个用途】
#
# - The time needed to re-start a failover after a previous failover was
# already tried against the same master by a given Sentinel, is two
# times the failover timeout. ---定语比较多，比较复杂，
# 抽出核心主谓宾：The time is two times the failover timeout.
#
# - The time needed for a slave replicating to a wrong master according
# to a Sentinel current configuration, to be forced to replicate
# with the right master, is exactly【确切地；恰好】 the failover timeout (counting since
# the moment a Sentinel detected the misconfiguration).##【从sentinel发现配置信息不准确时开始计时】
# 抽出核心主谓宾：The time is exactly the failover timeout.
#
# - The time needed to cancel a failover that is already in progress but
# did not produced any configuration change (SLAVEOF NO ONE yet not
# acknowledged by the promoted slave).
# 抽出核心主谓宾：The time needed to cancel a failover.
#
# - The maximum time a failover in progress waits for all the slaves to be
# reconfigured as slaves of the new master. However even after this time
# the slaves will be reconfigured by the Sentinels anyway, but not with
# the exact parallel-syncs progression as specified.
# 【however后面的意思是说：然而，不管怎么样，即是超过了这个定义的最大阈值，sentinel还是可以修改配置的；
#  但是，不是严格按照前面定义的parallel-syncs的方式，例如，不再是前面默认的一个一个slave节点处理了。】
# Default is 3 minutes.
sentinel failover-timeout mymaster 180000