################################# REPLICATION #################################

# Master-Replica replication. Use replicaof to make a Redis instance a copy of
# another Redis server. A few things to understand ASAP about Redis replication.
#
#   +------------------+      +---------------+
#   |      Master      | ---> |    Replica    |
#   | (receive writes) |      |  (exact copy) |
#   +------------------+      +---------------+
#
# 1) Redis replication is asynchronous, but you can configure a master to
#    stop accepting writes if it appears to be not connected with at least
#    a given number of replicas.
# 2) Redis replicas are able to perform a partial resynchronization with the
#    master if the replication link is lost for a relatively small amount of
#    time. You may want to configure the replication backlog size (see the next
#    sections of this file) with a sensible value depending on your needs.
# 3) Replication is automatic and does not need user intervention. After a
#    network partition replicas automatically try to reconnect to masters
#    and resynchronize with them.
#
# replicaof <masterip> <masterport>
replicaof 10.0.0.22 6379  #目标master节点的IP及端口信息，配置表示设置当前机器为slave节点，默认 注释禁用

# If the master is password protected (using the "requirepass" configuration
# directive below) it is possible to tell the replica to authenticate before
# starting the replication synchronization process, otherwise the master will
# refuse the replica request.
#
# masterauth <master-password>
masterauth redis  #目标master节点的连接密码

# When a replica loses its connection with the master, or when the replication
# is still in progress, the replica can act in two different ways:
#
# 1) if replica-serve-stale-data is set to 'yes' (the default) the replica will
#    still reply to client requests, possibly with out of date data, or the
#    data set may just be empty if this is the first synchronization.
#
# 2) if replica-serve-stale-data is set to 'no' the replica will reply with
#    an error "SYNC with master in progress" to all the kind of commands
#    but to INFO, replicaOF, AUTH, PING, SHUTDOWN, REPLCONF, ROLE, CONFIG,
#    SUBSCRIBE, UNSUBSCRIBE, PSUBSCRIBE, PUNSUBSCRIBE, PUBLISH, PUBSUB,
#    COMMAND, POST, HOST: and LATENCY.
#
replica-serve-stale-data yes #当slave失去与master连接或正在进行复制时，是否继续响应客户端读请求。会导致用户访问的数据未及时更新，默认：yes，建议设置为yes
#设置为no时除特定命令外任何请求返回错误"SYNC with master in progress"

# You can configure a replica instance to accept writes or not. Writing against
# a replica instance may be useful to store some ephemeral data (because data
# written on a replica will be easily deleted after resync with the master) but
# may also cause problems if clients are writing to it because of a
# misconfiguration.
#
# Since Redis 2.6 by default replicas are read-only.
#
# Note: read only replicas are not designed to be exposed to untrusted clients
# on the internet. It's just a protection layer against misuse of the instance.
# Still a read only replica exports by default all the administrative commands
# such as CONFIG, DEBUG, and so forth. To a limited extent you can improve
# security of read only replicas using 'rename-command' to shadow all the
# administrative / dangerous commands.
replica-read-only yes #slave节点只读 默认：yes

# Replication SYNC strategy: disk or socket.
#
# -------------------------------------------------------
# WARNING: DISKLESS REPLICATION IS EXPERIMENTAL CURRENTLY
# -------------------------------------------------------
#
# New replicas and reconnecting replicas that are not able to continue the replication
# process just receiving differences, need to do what is called a "full
# synchronization". An RDB file is transmitted from the master to the replicas.
# The transmission can happen in two different ways:
#
# 1) Disk-backed: The Redis master creates a new process that writes the RDB
#                 file on disk. Later the file is transferred by the parent
#                 process to the replicas incrementally.
# 2) Diskless: The Redis master creates a new process that directly writes the
#              RDB file to replica sockets, without touching the disk at all.
#
# With disk-backed replication, while the RDB file is generated, more replicas
# can be queued and served with the RDB file as soon as the current child producing
# the RDB file finishes its work. With diskless replication instead once
# the transfer starts, new replicas arriving will be queued and a new transfer
# will start when the current one terminates.
#
# When diskless replication is used, the master waits a configurable amount of
# time (in seconds) before starting the transfer in the hope that multiple replicas
# will arrive and the transfer can be parallelized.
#
# With slow disks and fast (large bandwidth) networks, diskless replication
# works better.
repl-diskless-sync no  #使用socket模式（无盘模式）进行rdb副本传输
#slave节点首次连接到master时需要进行数据全量复制，redis-server 需要将数据dump成新的rdb文件传输给slave端
# no ：基于硬盘（disk-backed）master创建一个新的子进程dump生成新的rdb磁盘文件，再由主进程将rdb磁盘文件传输至slave节点上
# yes ：基于socket(diskless) master创建一个新的子进程直接dump rdb数据至slave节点的网络socket，不经过磁盘和主进程操作
# 推荐基于磁盘（no）进行rdb数据传输，rdb文件创建后可同时传输给多个slave。基于socket传输(yes)，slave连接至master之后需要逐个传输，建议当磁盘I/O性能较差且网络环境较好时启用


# When diskless replication is enabled, it is possible to configure the delay
# the server waits in order to spawn the child that transfers the RDB via socket
# to the replicas.
#
# This is important since once the transfer starts, it is not possible to serve
# new replicas arriving, that will be queued for the next RDB transfer, so the server
# waits a delay in order to let more replicas arrive.
#
# The delay is specified in seconds, and by default is 5 seconds. To disable
# it entirely just set it to 0 seconds and the transfer will start ASAP.
repl-diskless-sync-delay 5 #rdb socket传输等待时间，默认 5s
# 在等待期间连接上master的slave，会一起通过socket方式同步rdb数据，当本次数据同步开始后，master将不再接受新的slave同步请求，等待时间后新连接的slave需排队等待下一次rdb数据同步
# 因此服务器需要等待一段时间才能让更多的副本到达，建议值：30-60

# Replicas send PINGs to server in a predefined interval. It's possible to change
# this interval with the repl_ping_replica_period option. The default value is 10
# seconds.
#
repl-ping-replica-period 10  #slave向master发起ping探测间隔时间（单位s），默认：5

# The following option sets the replication timeout for:
#
# 1) Bulk transfer I/O during SYNC, from the point of view of replica.
# 2) Master timeout from the point of view of replicas (data, pings).
# 3) Replica timeout from the point of view of masters (REPLCONF ACK pings).
#
# It is important to make sure that this value is greater than the value
# specified for repl-ping-replica-period otherwise a timeout will be detected
# every time there is low traffic between the master and the replica.
#
repl-timeout 60  #复制连接超时时间，须大于 repl-ping-replica-period ，默认：60

# Disable TCP_NODELAY on the replica socket after SYNC?
#
# If you select "yes" Redis will use a smaller number of TCP packets and
# less bandwidth to send data to replicas. But this can add a delay for
# the data to appear on the replica side, up to 40 milliseconds with
# Linux kernels using a default configuration.
#
# If you select "no" the delay for data to appear on the replica side will
# be reduced but more bandwidth will be used for replication.
#
# By default we optimize for low latency, but in very high traffic conditions
# or when the master and replicas are many hops away, turning this to "yes" may
# be a good idea.
repl-disable-tcp-nodelay no  #slave发起sync请求后禁用TCP-NODELAY
# yes：Redis将合并多个报文为一个大报文，从而使用少量数据包向slave发生数据，节约网络带宽，但会造成数据传输延迟，Linux内核默认延迟将到达40毫秒
# no：不对数据报文进行合并，降低数据延迟，但将占用更高的带宽


# Set the replication backlog size. The backlog is a buffer that accumulates
# replica data when replicas are disconnected for some time, so that when a replica
# wants to reconnect again, often a full resync is not needed, but a partial
# resync is enough, just passing the portion of data the replica missed while
# disconnected.
#
# The bigger the replication backlog, the longer the time the replica can be
# disconnected and later be able to perform a partial resynchronization.
#
# The backlog is only allocated once there is at least a replica connected.
#
repl-backlog-size 128mb #复制缓冲区内存大小，默认：1
#在slave断开连接后。缓冲区将累积复制副本数据，当slave重连后仅需要进行增量复制避免全量复制，只在有slave连接时分配此内存空间，建议适当调大此分配空间，否则将导致slave数据同步失败

# After a master has no longer connected replicas for some time, the backlog
# will be freed. The following option configures the amount of seconds that
# need to elapse, starting from the time the last replica disconnected, for
# the backlog buffer to be freed.
#
# Note that replicas never free the backlog for timeout, since they may be
# promoted to masters later, and should be able to correctly "partially
# resynchronize" with the replicas: hence they should always accumulate backlog.
#
# A value of 0 means to never release the backlog.
#
repl-backlog-ttl 3600 #复制缓冲区有效期限，超过此期限没有slave连接，缓冲区空间将被释放

# The replica priority is an integer number published by Redis in the INFO output.
# It is used by Redis Sentinel in order to select a replica to promote into a
# master if the master is no longer working correctly.
#
# A replica with a low priority number is considered better for promotion, so
# for instance if there are three replicas with priority 10, 100, 25 Sentinel will
# pick the one with priority 10, that is the lowest.
#
# However a special priority of 0 marks the replica as not able to perform the
# role of master, so a replica with priority of 0 will never be selected by
# Redis Sentinel for promotion.
#
# By default the priority is 100.
replica-priority 100  #哨兵选举master优先级，数值越小优先级越高，为0时永远不会被选举，默认：100

# It is possible for a master to stop accepting writes if there are less than
# N replicas connected, having a lag less or equal than M seconds.
#
# The N replicas need to be in "online" state.
#
# The lag in seconds, that must be <= the specified value, is calculated from
# the last ping received from the replica, that is usually sent every second.
#
# This option does not GUARANTEE that N replicas will accept the write, but
# will limit the window of exposure for lost writes in case not enough replicas
# are available, to the specified number of seconds.
#
# For example to require at least 3 replicas with a lag <= 10 seconds use:
#
# min-replicas-to-write 1  #允许master执行写入操作的slave最少连接数，默认：3禁用
# min-replicas-max-lag 10  #允许master执行写入操作的slave最少连接数的最大超时时限，默认：10 禁用
#
# Setting one or the other to 0 disables the feature.
#
# By default min-replicas-to-write is set to 0 (feature disabled) and
# min-replicas-max-lag is set to 10.

replicaof 10.0.0.22 6379
masterauth redis

[root@Redis-Ubuntu-1804-p22:~]# redis-cli -a redis -p 6379 --no-auth-warning info replication
# Replication
role:master
connected_slaves:0
master_replid:c0b96732e4879ff1e2e0240ff64fcd61e42e1df2
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:0
second_repl_offset:-1
repl_backlog_active:0
repl_backlog_size:1048576
repl_backlog_first_byte_offset:0
repl_backlog_histlen:0
[root@Redis-Ubuntu-1804-p22:~]# redis-cli -a redis -p 6379 --no-auth-warning info replication
# Replication
role:master
connected_slaves:1
slave0:ip=10.0.0.21,port=6379,state=wait_bgsave,offset=0,lag=0
master_replid:15f2ce5d08cf48fae39c85d8e1c7eddc591e6019
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:0
second_repl_offset:-1
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:1
repl_backlog_histlen:0
[root@Redis-Ubuntu-1804-p22:~]# redis-cli -a redis -p 6379 --no-auth-warning info replication
# Replication
role:master
connected_slaves:1
slave0:ip=10.0.0.21,port=6379,state=online,offset=1050,lag=1
master_replid:15f2ce5d08cf48fae39c85d8e1c7eddc591e6019
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:1050
second_repl_offset:-1
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:1
repl_backlog_histlen:1050
[root@Redis-Ubuntu-1804-p22:~]#

[root@Redis-Ubuntu-1804-p22:~]# redis-cli -a redis -p 6379 --no-auth-warning info replication
# Replication
role:master
connected_slaves:2
slave0:ip=10.0.0.21,port=6379,state=online,offset=4923406,lag=1
slave1:ip=10.0.0.20,port=6379,state=online,offset=4923406,lag=1
master_replid:15f2ce5d08cf48fae39c85d8e1c7eddc591e6019
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:4923406
second_repl_offset:-1
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:3874831
repl_backlog_histlen:1048576