Redis进阶

save 900 1：表示900 秒内如果至少有 1 个 key 的值变化，则保存
save 300 10：表示300 秒内如果至少有 10 个 key 的值变化，则保存
save 60 10000：表示60 秒内如果至少有 10000 个 key 的值变化，则保存

redis-check-aof  --fix appendonly.aof
一般不会出错，出错基本也是人为的！有内鬼

cp redis.conf redis-6380.conf
cp redis.conf redis-6381.conf

slaveof 127.0.0.1 6379
info replication //观察信息

slaveof no one

1. 连接建立阶段
该阶段的主要作用是在主从节点之间建立连接，为数据同步做好准备。
步骤1：保存主节点信息
​
从节点服务器内部维护了两个字段，即masterhost和masterport字段，用于存储主节点的ip和port信息。
​
需要注意的是，slaveof是异步命令，从节点完成主节点ip和port的保存后，向发送slaveof命令的客户端直接返回OK，实际的复制操作在这之后才开始进行。
​
​
​
步骤2：建立socket连接（套接字）
​
从节点每秒1次调用复制定时函数replicationCron()，如果发现了有主节点可以连接，便会根据主节点的ip和port，创建socket连接。如果连接成功，则：
​
从节点：为该socket建立一个专门处理复制工作的文件事件处理器，负责后续的复制工作，如接收RDB文件、接收命令传播等。
​
主节点：接收到从节点的socket连接后（即accept之后），为该socket创建相应的客户端状态，并将从节点看做是连接到主节点的一个客户端，后面的步骤会以从节点向主节点发送命令请求的形式来进行。
​
​
​
步骤3：发送ping命令
​
从节点成为主节点的客户端之后，发送ping命令进行首次请求，目的是：检查socket连接是否可用，以及主节点当前是否能够处理请求。
​
从节点发送ping命令后，可能出现3种情况：
​
（1）返回pong：说明socket连接正常，且主节点当前可以处理请求，复制过程继续。
​
（2）超时：一定时间后从节点仍未收到主节点的回复，说明socket连接不可用，则从节点断开socket连接，并重连。
​
（3）返回pong以外的结果：如果主节点返回其他结果，如正在处理超时运行的脚本，说明主节点当前无法处理命令，则从节点断开socket连接，并重连。
​
步骤4：身份验证
​
如果从节点中设置了masterauth选项，则从节点需要向主节点进行身份验证；没有设置该选项，则不需要验证。从节点进行身份验证是通过向主节点发送auth命令进行的，auth命令的参数即为配置文件中的masterauth的值。
​
如果主节点设置密码的状态，与从节点masterauth的状态一致（一致是指都存在，且密码相同，或者都不存在），则身份验证通过，复制过程继续；如果不一致，则从节点断开socket连接，并重连。
步骤5：发送从节点端口信息
​
身份验证之后，从节点会向主节点发送其监听的端口号（前述例子中为6380），主节点将该信息保存到该从节点对应的客户端的slave_listening_port字段中；该端口信息除了在主节点中执行info Replication时显示以外，没有其他作用。
2. 数据同步阶段
​
主从节点之间的连接建立以后，便可以开始进行数据同步，该阶段可以理解为从节点数据的初始化。具体执行的方式是：从节点向主节点发送psync命令（Redis2.8以前是sync命令），开始同步。
​
数据同步阶段是主从复制最核心的阶段，根据主从节点当前状态的不同，可以分为全量复制和增量复制
​
需要注意的是，在数据同步阶段之前，从节点是主节点的客户端，主节点不是从节点的客户端；而到了这一阶段及以后，主从节点互为客户端。原因在于：在此之前，主节点只需要响应从节点的请求即可，不需要主动发请求，而在数据同步阶段和后面的命令传播阶段，主节点需要主动向从节点发送请求（如推送缓冲区中的写命令），才能完成复制。
3. 命令传播阶段
​
数据同步阶段完成后，主从节点进入命令传播阶段；在这个阶段主节点将自己执行的写命令发送给从节点，从节点接收命令并执行，从而保证主从节点数据的一致性。
​
在命令传播阶段，除了发送写命令，主从节点还维持着心跳机制：PING和REPLCONF ACK。
​
延迟与不一致
​
需要注意的是，命令传播是异步的过程，即主节点发送写命令后并不会等待从节点的回复；因此实际上主从节点之间很难保持实时的一致性，延迟在所难免。数据不一致的程度，与主从节点之间的网络状况、主节点写命令的执行频率、以及主节点中的repl-disable-tcp-nodelay配置等有关。
​
repl-disable-tcp-nodelay no：该配置作用于命令传播阶段，控制主节点是否禁止与从节点的TCP_NODELAY；默认no，即不禁止TCP_NODELAY。当设置为yes时，TCP会对包进行合并从而减少带宽，但是发送的频率会降低，从节点数据延迟增加，一致性变差；具体发送频率与Linux内核的配置有关，默认配置为40ms。当设置为no时，TCP会立马将主节点的数据发送给从节点，带宽增加但延迟变小。
​
一般来说，只有当应用对Redis数据不一致的容忍度较高，且主从节点之间网络状况不好时，才会设置为yes；多数情况使用默认值no。

  port 26380
  protected-mode no
  daemonize yes
  pidfile "/var/run/redis-sentinel_26380.pid"
  logfile "/var/log/redis/sentinel_26380.log"
  dir "/tmp"
   #避免脚本重置，默认值yes
  sentinel deny-scripts-reconfig yes
​
 #告诉sentinel去监听地址为ip:port的一个master，这里的master-name可以自定义，quorum是一个数字，指明当有多少个sentinel认为一个master失效时，master才算真正失效 ，要加外网地址
  sentinel monitor mymaster xxxx 6379 1 (xxxx是地址)
​
  #这个配置项指定了需要多少失效时间，一个master才会被这个sentinel主观地认为是不可用的。 单位是毫秒，默认为30秒
  sentinel down-after-milliseconds mymaster 30000
​
  #指定了在发生failover主备切换时最多可以有多少个slave同时对新的 master进行 同步.这个数字越小，完成failover所需的时间就越长，但是如果这个数字越大，就意味着越 多的slave因为replication而不可用.可以通过将这个值设为 1 来保证每次只有一个slave 处于不能处理命令请求的状态。
  sentinel parallel-syncs mymaster 1
​
  #当进行failover故障转移时，配置所有slaves指向新的master所需的最大时间
  sentinel failover-timeout mymaster 180000
​
   #master-name的验证密码（如果你有的话）
 # sentinel auth-pass mymaster 123456
​

# Example sentinel.conf
​
# *** IMPORTANT ***
#
# By default Sentinel will not be reachable from interfaces different than
# localhost, either use the 'bind' directive to bind to a list of network
# interfaces, or disable protected mode with "protected-mode no" by
# adding it to this configuration file.
#
# Before doing that MAKE SURE the instance is protected from the outside
# world via firewalling or other means.
#
# For example you may use one of the following:
#
# bind 127.0.0.1 192.168.1.1
#
# protected-mode no
​
# port <sentinel-port>
# The port that this sentinel instance will run on
port 26380
​
# By default Redis Sentinel does not run as a daemon. Use 'yes' if you need it.
# Note that Redis will write a pid file in /var/run/redis-sentinel.pid when
# daemonized.
daemonize yes
​
# When running daemonized, Redis Sentinel writes a pid file in
# /var/run/redis-sentinel.pid by default. You can specify a custom pid file
# location here.
pidfile "/var/run/redis-sentinel_26380.pid"
​
# Specify the log file name. Also the empty string can be used to force
# Sentinel to log on the standard output. Note that if you use standard
# output for logging but daemonize, logs will be sent to /dev/null
logfile "/var/log/redis/sentinel_26380.log"
​
# sentinel announce-ip <ip>
# sentinel announce-port <port>
#
# The above two configuration directives are useful in environments where,
# because of NAT, Sentinel is reachable from outside via a non-local address.
#
# When announce-ip is provided, the Sentinel will claim the specified IP address
# in HELLO messages used to gossip its presence, instead of auto-detecting the
# local address as it usually does.
#
# Similarly when announce-port is provided and is valid and non-zero, Sentinel
# will announce the specified TCP port.
#
# The two options don't need to be used together, if only announce-ip is
# provided, the Sentinel will announce the specified IP and the server port
# as specified by the "port" option. If only announce-port is provided, the
# Sentinel will announce the auto-detected local IP and the specified port.
#
# Example:
#
# sentinel announce-ip 1.2.3.4
​
# dir <working-directory>
# Every long running process should have a well-defined working directory.
# For Redis Sentinel to chdir to /tmp at startup is the simplest thing
# for the process to don't interfere with administrative tasks such as
# unmounting filesystems.
dir "/tmp"
​
# sentinel monitor <master-name> <ip> <redis-port> <quorum>
#
# Tells Sentinel to monitor this master, and to consider it in O_DOWN
# (Objectively Down) state only if at least <quorum> sentinels agree.
#
# Note that whatever is the ODOWN quorum, a Sentinel will require to
# be elected by the majority of the known Sentinels in order to
# start a failover, so no failover can be performed in minority.
#
# Replicas are auto-discovered, so you don't need to specify replicas in
# any way. Sentinel itself will rewrite this configuration file adding
# the replicas using additional configuration options.
# Also note that the configuration file is rewritten when a
# replica is promoted to master.
#
# Note: master name should not include special characters or spaces.
# The valid charset is A-z 0-9 and the three characters ".-_".
sentinel myid 425a5893faf6a2811b3061093f8331e18461f98b
​
# sentinel auth-pass <master-name> <password>
#
# Set the password to use to authenticate with the master and replicas.
# Useful if there is a password set in the Redis instances to monitor.
#
# Note that the master password is also used for replicas, so it is not
# possible to set a different password in masters and replicas instances
# if you want to be able to monitor these instances with Sentinel.
#
# However you can have Redis instances without the authentication enabled
# mixed with Redis instances requiring the authentication (as long as the
# password set is the same for all the instances requiring the password) as
# the AUTH command will have no effect in Redis instances with authentication
# switched off.
#
# Example:
#
# sentinel auth-pass mymaster MySUPER--secret-0123passw0rd
​
# sentinel auth-user <master-name> <username>
#
# This is useful in order to authenticate to instances having ACL capabilities,
# that is, running Redis 6.0 or greater. When just auth-pass is provided the
# Sentinel instance will authenticate to Redis using the old "AUTH <pass>"
# method. When also an username is provided, it will use "AUTH <user> <pass>".
# In the Redis servers side, the ACL to provide just minimal access to
# Sentinel instances, should be configured along the following lines:
#
#     user sentinel-user >somepassword +client +subscribe +publish \
#                        +ping +info +multi +slaveof +config +client +exec on
​
# sentinel down-after-milliseconds <master-name> <milliseconds>
#
# Number of milliseconds the master (or any attached replica 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).
#
# Default is 30 seconds.
sentinel monitor mymaster xxx.xx.xx.xxx 6380 1
​
# requirepass <password>
#
# You can configure Sentinel itself to require a password, however when doing
# so Sentinel will try to authenticate with the same password to all the
# other Sentinels. So you need to configure all your Sentinels in a given
# group with the same "requirepass" password. Check the following documentation
# for more info: https://redis.io/topics/sentinel
​
# sentinel parallel-syncs <master-name> <numreplicas>
#
# How many replicas we can reconfigure to point to the new replica simultaneously
# during the failover. Use a low number if you use the replicas to serve query
# to avoid that all the replicas will be unreachable at about the same
# time while performing the synchronization with the master.
sentinel config-epoch mymaster 0
​
# sentinel failover-timeout <master-name> <milliseconds>
#
# Specifies the failover timeout in milliseconds. It is used in many ways:
#
# - 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.
#
# - The time needed for a replica replicating to a wrong master according
#   to a Sentinel current configuration, to be forced to replicate
#   with the right master, is exactly the failover timeout (counting since
#   the moment a Sentinel detected the misconfiguration).
#
# - 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 replica).
#
# - The maximum time a failover in progress waits for all the replicas to be
#   reconfigured as replicas of the new master. However even after this time
#   the replicas will be reconfigured by the Sentinels anyway, but not with
#   the exact parallel-syncs progression as specified.
#
# Default is 3 minutes.
sentinel leader-epoch mymaster 0
​
# SCRIPTS EXECUTION
#
# sentinel notification-script and sentinel reconfig-script are used in order
# to configure scripts that are called to notify the system administrator
# or to reconfigure clients after a failover. The scripts are executed
# with the following rules for error handling:
#
# If script exits with "1" the execution is retried later (up to a maximum
# number of times currently set to 10).
#
# If script exits with "2" (or an higher value) the script execution is
# not retried.
#
# If script terminates because it receives a signal the behavior is the same
# as exit code 1.
#
# A script has a maximum running time of 60 seconds. After this limit is
# reached the script is terminated with a SIGKILL and the execution retried.
​
# NOTIFICATION SCRIPT
#
# sentinel notification-script <master-name> <script-path>
#
# Call the specified notification script for any sentinel event that is
# generated in the WARNING level (for instance -sdown, -odown, and so forth).
# This script should notify the system administrator via email, SMS, or any
# other messaging system, that there is something wrong with the monitored
# Redis systems.
#
# The script is called with just two arguments: the first is the event type
# and the second the event description.
#
# The script must exist and be executable in order for sentinel to start if
# this option is provided.
#
# Example:
#
# sentinel notification-script mymaster /var/redis/notify.sh
​
# CLIENTS RECONFIGURATION SCRIPT
#
# sentinel client-reconfig-script <master-name> <script-path>
#
# When the master changed because of a failover a script can be called in
# order to perform application-specific tasks to notify the clients that the
# configuration has changed and the master is at a different address.
#
# The following arguments are passed to the script:
#
# <master-name> <role> <state> <from-ip> <from-port> <to-ip> <to-port>
#
# <state> is currently always "failover"
# <role> is either "leader" or "observer"
#
# The arguments from-ip, from-port, to-ip, to-port are used to communicate
# the old address of the master and the new address of the elected replica
# (now a master).
#
# This script should be resistant to multiple invocations.
#
# Example:
#
# sentinel client-reconfig-script mymaster /var/redis/reconfig.sh
​
# SECURITY
#
# By default SENTINEL SET will not be able to change the notification-script
# and client-reconfig-script at runtime. This avoids a trivial security issue
# where clients can set the script to anything and trigger a failover in order
# to get the program executed.
​
#sentinel deny-scripts-reconfig yes
​
# REDIS COMMANDS RENAMING
#
# Sometimes the Redis server has certain commands, that are needed for Sentinel
# to work correctly, renamed to unguessable strings. This is often the case
# of CONFIG and SLAVEOF in the context of providers that provide Redis as
# a service, and don't want the customers to reconfigure the instances outside
# of the administration console.
#
# In such case it is possible to tell Sentinel to use different command names
# instead of the normal ones. For example if the master "mymaster", and the
# associated replicas, have "CONFIG" all renamed to "GUESSME", I could use:
#
# SENTINEL rename-command mymaster CONFIG GUESSME
#
# After such configuration is set, every time Sentinel would use CONFIG it will
# use GUESSME instead. Note that there is no actual need to respect the command
# case, so writing "config guessme" is the same in the example above.
#
# SENTINEL SET can also be used in order to perform this configuration at runtime.
#
# In order to set a command back to its original name (undo the renaming), it
# is possible to just rename a command to itsef:
#
# SENTINEL rename-command mymaster CONFIG CONFIG
# Generated by CONFIG REWRITE
​
​

redis-sentinel  xxx/sentinel.conf

public static void testSentinel() throws Exception {
         String masterName = "mymaster";
         Set<String> sentinels = new HashSet<>();
         sentinels.add("192.168.92.128:26379");
         sentinels.add("192.168.92.128:26380");
         sentinels.add("192.168.92.128:26381");
 
         JedisSentinelPool pool = new JedisSentinelPool(masterName, sentinels); //初始化过程做了很多工作
         Jedis jedis = pool.getResource();
         jedis.set("key1", "value1");
         pool.close();
}

加依赖
<dependency>
 <groupId>org.apache.commons</groupId>
 <artifactId>commons-pool2</artifactId>
</dependency>

spring:
  redis:
    pool:
    # 连接池最大连接数(使用负值表示没有限制) 默认为8
      max-active: 8
    # 连接池中的最大空闲连接 默认为8
      max-idle: 8
    # 连接池最大阻塞等待时间(使用负值表示没有限制) 默认为-1
      max-wait: -1ms
    # 连接池中的最小空闲连接 默认为 0
      min-idle: 0
    sentinel:
      # 主节点的别名
      master: mymaster
      # sentinel服务的ip和端口
      nodes: 110.40.154.233:26379
server:
  port: 8081
  
  // Reconnected to 110.40.154.233:6381你能看到springboot日志打出来这种日志你就成功了，但是请你注意在你搭建主从复制的时候一定要info replication看一下主从的关系，确定好再去开哨兵

（1）定时任务：每个哨兵节点维护了3个定时任务。定时任务的功能分别如下：通过向主从节点发送info命令获取最新的主从结构；通过发布订阅功能获取其他哨兵节点的信息；通过向其他节点发送ping命令进行心跳检测，判断是否下线。

（2）主观下线：在心跳检测的定时任务中，如果其他节点超过一定时间没有回复，哨兵节点就会将其进行主观下线。顾名思义，主观下线的意思是一个哨兵节点“主观地”判断下线；与主观下线相对应的是客观下线。

（3）客观下线：哨兵节点在对主节点进行主观下线后，会通过sentinel is-master-down-by-addr命令询问其他哨兵节点该主节点的状态；如果判断主节点下线的哨兵数量达到一定数值，则对该主节点进行客观下线。

需要特别注意的是，客观下线是主节点才有的概念；如果从节点和哨兵节点发生故障，被哨兵主观下线后，不会再有后续的客观下线和故障转移操作。

（4）选举领导者哨兵节点：当主节点被判断客观下线以后，各个哨兵节点会进行协商，选举出一个领导者哨兵节点，并由该领导者节点对其进行故障转移操作。

监视该主节点的所有哨兵都有可能被选为领导者，选举使用的算法是Raft算法；Raft算法的基本思路是先到先得：即在一轮选举中，哨兵A向B发送成为领导者的申请，如果B没有同意过其他哨兵，则会同意A成为领导者。选举的具体过程这里不做详细描述，一般来说，哨兵选择的过程很快，谁先完成客观下线，一般就能成为领导者。

（5）故障转移：选举出的领导者哨兵，开始进行故障转移操作，该操作大体可以分为3个步骤：

    在从节点中选择新的主节点：选择的原则是，首先过滤掉不健康的从节点；然后选择优先级最高的从节点(由slave-priority指定)；如果优先级无法区分，则选择复制偏移量最大的从节点；如果仍无法区分，则选择runid最小的从节点。
    更新主从状态：通过slaveof no one命令，让选出来的从节点成为主节点；并通过slaveof命令让其他节点成为其从节点。
    将已经下线的主节点(即6379)设置为新的主节点的从节点，当6379重新上线后，它会成为新的主节点的从节点。

概念
访问一个不存在的key，缓存不起作用，请求会穿透到DB，流量大时DB会挂掉。
解决方案
采用布隆过滤器，使用一个足够大的bitmap，用于存储可能访问的key，不存在的key直接被过滤；
访问key未在DB查询到值，也将空值写进缓存，但可以设置较短过期时间。

概念
一个存在的key，在缓存过期的一刻，同时有大量的请求，这些请求都会击穿到DB，造成瞬时DB请求量大、压力骤增。
解决方案
在访问key之前，采用SETNX（set if not exists）来设置另一个短期key来锁住当前key的访问，访问结束再删除该短期key。

概念
大量的key设置了相同的过期时间，导致在缓存在同一时刻全部失效，造成瞬时DB请求量大、压力骤增，引起雪崩。
解决方案
可以给缓存设置过期时间时加上一个随机值时间，使得每个key的过期时间分布开来，不会集中在同一时刻失效。