Redis configuration file example.
Note that in order to read the configuration file, Redis must be
started with the file path as first argument:
Note on units: when memory size is needed, it is possible to specify
it in the usual form of 1k 5GB 4M and so forth:
1k => 1000 bytes
1kb => 1024 bytes
1m => 1000000 bytes
1mb => 1024*1024 bytes
1g => 1000000000 bytes
1gb => 102410241024 bytes
units are case insensitive so 1GB 1Gb 1gB are all the same.
Include one or more other config files here. This is useful if you
have a standard template that goes to all Redis servers but also need
to customize a few per-server settings. Include files can include
other files, so use this wisely.
Notice option "include" won't be rewritten by command "CONFIG REWRITE"
from admin or Redis Sentinel. Since Redis always uses the last processed
line as value of a configuration directive, you'd better put includes
at the beginning of this file to avoid overwriting config change at runtime.
If instead you are interested in using includes to override configuration
options, it is better to use include as the last line.
Load modules at startup. If the server is not able to load modules
it will abort. It is possible to use multiple loadmodule directives.
By default, if no "bind" configuration directive is specified, Redis listens
for connections from all the network interfaces available on the server.
It is possible to listen to just one or multiple selected interfaces using
the "bind" configuration directive, followed by one or more IP addresses.
bind 192.168.1.100 10.0.0.1
bind 127.0.0.1 ::1
~ WARNING ~ If the computer running Redis is directly exposed to the
internet, binding to all the interfaces is dangerous and will expose the
instance to everybody on the internet. So by default we uncomment the
following bind directive, that will force Redis to listen only into
the IPv4 loopback interface address (this means Redis will be able to
accept connections only from clients running into the same computer it
IF YOU ARE SURE YOU WANT YOUR INSTANCE TO LISTEN TO ALL THE INTERFACES
JUST COMMENT THE FOLLOWING LINE.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~~
Protected mode is a layer of security protection, in order to avoid that
Redis instances left open on the internet are accessed and exploited.
When protected mode is on and if:
1) The server is not binding explicitly to a set of addresses using the
2) No password is configured.
The server only accepts connections from clients connecting from the
IPv4 and IPv6 loopback addresses 127.0.0.1 and ::1, and from Unix domain
By default protected mode is enabled. You should disable it only if
you are sure you want clients from other hosts to connect to Redis
even if no authentication is configured, nor a specific set of interfaces
are explicitly listed using the "bind" directive.
Accept connections on the specified port, default is 6379 (IANA #815344).
If port 0 is specified Redis will not listen on a TCP socket.
TCP listen() backlog.
In high requests-per-second environments you need an high backlog in order
to avoid slow clients connections issues. Note that the Linux kernel
will silently truncate it to the value of /proc/sys/net/core/somaxconn so
make sure to raise both the value of somaxconn and tcp_max_syn_backlog
in order to get the desired effect.
Specify the path for the Unix socket that will be used to listen for
incoming connections. There is no default, so Redis will not listen
on a unix socket when not specified.
Close the connection after a client is idle for N seconds (0 to disable)
If non-zero, use SO_KEEPALIVE to send TCP ACKs to clients in absence
of communication. This is useful for two reasons:
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 300 seconds, which is the new
Redis default starting with Redis 3.2.1.
By default Redis does not run as a daemon. Use 'yes' if you need it.
Note that Redis will write a pid file in /var/run/redis.pid when daemonized.
If you run Redis from upstart or systemd, Redis can interact with your
supervision tree. Options:
supervised no - no supervision interaction
supervised upstart - signal upstart by putting Redis into SIGSTOP mode
supervised systemd - signal systemd by writing READY=1 to $NOTIFY_SOCKET
supervised auto - detect upstart or systemd method based on
UPSTART_JOB or NOTIFY_SOCKET environment variables
Note: these supervision methods only signal "process is ready."
They do not enable continuous liveness pings back to your supervisor.
If a pid file is specified, Redis writes it where specified at startup
and removes it at exit.
When the server runs non daemonized, no pid file is created if none is
specified in the configuration. When the server is daemonized, the pid file
is used even if not specified, defaulting to "/var/run/redis.pid".
Creating a pid file is best effort: if Redis is not able to create it
nothing bad happens, the server will start and run normally.
Specify the server verbosity level.
This can be one of:
debug (a lot of information, useful for development/testing)
verbose (many rarely useful info, but not a mess like the debug level)
notice (moderately verbose, what you want in production probably)
warning (only very important / critical messages are logged)
Specify the log file name. Also the empty string can be used to force
Redis to log on the standard output. Note that if you use standard
output for logging but daemonize, logs will be sent to /dev/null
To enable logging to the system logger, just set 'syslog-enabled' to yes,
and optionally update the other syslog parameters to suit your needs.
Specify the syslog identity.
Specify the syslog facility. Must be USER or between LOCAL0-LOCAL7.
Set the number of databases. The default database is DB 0, you can select
a different one on a per-connection basis using SELECT <dbid> where
dbid is a number between 0 and 'databases'-1
By default Redis shows an ASCII art logo only when started to log to the
standard output and if the standard output is a TTY. Basically this means
that normally a logo is displayed only in interactive sessions.
However it is possible to force the pre-4.0 behavior and always show a
ASCII art logo in startup logs by setting the following option to yes.
Save the DB on disk:
save <seconds> <changes>
Will save the DB if both the given number of seconds and the given
number of write operations against the DB occurred.
In the example below the behaviour will be to save:
after 900 sec (15 min) if at least 1 key changed
after 300 sec (5 min) if at least 10 keys changed
after 60 sec if at least 10000 keys changed
Note: you can disable saving completely by commenting out all "save" lines.
It is also possible to remove all the previously configured save
points by adding a save directive with a single empty string argument
like in the following example:
save 900 1
save 300 10
save 60 10000
By default Redis will stop accepting writes if RDB snapshots are enabled
(at least one save point) and the latest background save failed.
This will make the user aware (in a hard way) that data is not persisting
on disk properly, otherwise chances are that no one will notice and some
disaster will happen.
If the background saving process will start working again Redis will
automatically allow writes again.
However if you have setup your proper monitoring of the Redis server
and persistence, you may want to disable this feature so that Redis will
continue to work as usual even if there are problems with disk,
permissions, and so forth.
Compress string objects using LZF when dump .rdb databases?
For default that's set to 'yes' as it's almost always a win.
If you want to save some CPU in the saving child set it to 'no' but
the dataset will likely be bigger if you have compressible values or keys.
Since version 5 of RDB a CRC64 checksum is placed at the end of the file.
This makes the format more resistant to corruption but there is a performance
hit to pay (around 10%) when saving and loading RDB files, so you can disable it
for maximum performances.
RDB files created with checksum disabled have a checksum of zero that will
tell the loading code to skip the check.
The filename where to dump the DB
The working directory.
The DB will be written inside this directory, with the filename specified
above using the 'dbfilename' configuration directive.
The Append Only File will also be created inside this directory.
Note that you must specify a directory here, not a file name.
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>
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.
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.
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
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.
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
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.
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
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.
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.
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
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.
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.
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.
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:
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.
A Redis master is able to list the address and port of the attached
replicas in different ways. For example the "INFO replication" section
offers this information, which is used, among other tools, by
Redis Sentinel in order to discover replica instances.
Another place where this info is available is in the output of the
"ROLE" command of a master.
The listed IP and address normally reported by a replica is obtained
in the following way:
IP: The address is auto detected by checking the peer address
of the socket used by the replica to connect with the master.
Port: The port is communicated by the replica during the replication
handshake, and is normally the port that the replica is using to
listen for connections.
However when port forwarding or Network Address Translation (NAT) is
used, the replica may be actually reachable via different IP and port
pairs. The following two options can be used by a replica in order to
report to its master a specific set of IP and port, so that both INFO
and ROLE will report those values.
There is no need to use both the options if you need to override just
the port or the IP address.
Require clients to issue AUTH <PASSWORD> before processing any other
commands. This might be useful in environments in which you do not trust
others with access to the host running redis-server.
This should stay commented out for backward compatibility and because most
people do not need auth (e.g. they run their own servers).
Warning: since Redis is pretty fast an outside user can try up to
150k passwords per second against a good box. This means that you should
use a very strong password otherwise it will be very easy to break.
It is possible to change the name of dangerous commands in a shared
environment. For instance the CONFIG command may be renamed into something
hard to guess so that it will still be available for internal-use tools
but not available for general clients.
rename-command CONFIG b840fc02d524045429941cc15f59e41cb7be6c52
It is also possible to completely kill a command by renaming it into
an empty string:
rename-command CONFIG ""
Please note that changing the name of commands that are logged into the
AOF file or transmitted to replicas may cause problems.
Set the max number of connected clients at the same time. By default
this limit is set to 10000 clients, however if the Redis server is not
able to configure the process file limit to allow for the specified limit
the max number of allowed clients is set to the current file limit
minus 32 (as Redis reserves a few file descriptors for internal uses).
Once the limit is reached Redis will close all the new connections sending
an error 'max number of clients reached'.
Set a memory usage limit to the specified amount of bytes.
When the memory limit is reached Redis will try to remove keys
according to the eviction policy selected (see maxmemory-policy).
If Redis can't remove keys according to the policy, or if the policy is
set to 'noeviction', Redis will start to reply with errors to commands
that would use more memory, like SET, LPUSH, and so on, and will continue
to reply to read-only commands like GET.
This option is usually useful when using Redis as an LRU or LFU cache, or to
set a hard memory limit for an instance (using the 'noeviction' policy).
WARNING: If you have replicas attached to an instance with maxmemory on,
the size of the output buffers needed to feed the replicas 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 replicas 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 replicas attached it is suggested that you set a lower
limit for maxmemory so that there is some free RAM on the system for replica
output buffers (but this is not needed if the policy is 'noeviction').
MAXMEMORY POLICY: how Redis will select what to remove when maxmemory
is reached. You can select among five behaviors:
volatile-lru -> Evict using approximated LRU among the keys with an expire set.
allkeys-lru -> Evict any key using approximated LRU.
volatile-lfu -> Evict using approximated LFU among the keys with an expire set.
allkeys-lfu -> Evict any key using approximated LFU.
volatile-random -> Remove a random key among the ones with an expire set.
allkeys-random -> Remove a random key, any key.
volatile-ttl -> Remove the key with the nearest expire time (minor TTL)
noeviction -> Don't evict anything, just return an error on write operations.
LRU means Least Recently Used
LFU means Least Frequently Used
Both LRU, LFU and volatile-ttl are implemented using approximated
Note: with any of the above policies, Redis will return an error on write
operations, when there are no suitable keys for eviction.
At the date of writing these commands are: set setnx setex append
incr decr rpush lpush rpushx lpushx linsert lset rpoplpush sadd
sinter sinterstore sunion sunionstore sdiff sdiffstore zadd zincrby
zunionstore zinterstore hset hsetnx hmset hincrby incrby decrby
getset mset msetnx exec sort
The default is:
LRU, LFU and minimal TTL algorithms are not precise algorithms but approximated
algorithms (in order to save memory), so you can tune it for speed or
accuracy. For default Redis will check five keys and pick the one that was
used less recently, you can change the sample size using the following
The default of 5 produces good enough results. 10 Approximates very closely
true LRU but costs more CPU. 3 is faster but not very accurate.
Starting from Redis 5, by default a replica will ignore its maxmemory setting
(unless it is promoted to master after a failover or manually). It means
that the eviction of keys will be just handled by the master, sending the
DEL commands to the replica as keys evict in the master side.
This behavior ensures that masters and replicas stay consistent, and is usually
what you want, however if your replica is writable, or you want the replica to have
a different memory setting, and you are sure all the writes performed to the
replica are idempotent, then you may change this default (but be sure to understand
what you are doing).
Note that since the replica by default does not evict, it may end using more
memory than the one set via maxmemory (there are certain buffers that may
be larger on the replica, or data structures may sometimes take more memory and so
forth). So make sure you monitor your replicas and make sure they have enough
memory to never hit a real out-of-memory condition before the master hits
the configured maxmemory setting.
Redis has two primitives to delete keys. One is called DEL and is a blocking
deletion of the object. It means that the server stops processing new commands
in order to reclaim all the memory associated with an object in a synchronous
way. If the key deleted is associated with a small object, the time needed
in order to execute the DEL command is very small and comparable to most other
O(1) or O(log_N) commands in Redis. However if the key is associated with an
aggregated value containing millions of elements, the server can block for
a long time (even seconds) in order to complete the operation.
For the above reasons Redis also offers non blocking deletion primitives
such as UNLINK (non blocking DEL) and the ASYNC option of FLUSHALL and
FLUSHDB commands, in order to reclaim memory in background. Those commands
are executed in constant time. Another thread will incrementally free the
object in the background as fast as possible.
DEL, UNLINK and ASYNC option of FLUSHALL and FLUSHDB are user-controlled.
It's up to the design of the application to understand when it is a good
idea to use one or the other. However the Redis server sometimes has to
delete keys or flush the whole database as a side effect of other operations.
Specifically Redis deletes objects independently of a user call in the
1) On eviction, because of the maxmemory and maxmemory policy configurations,
in order to make room for new data, without going over the specified
2) Because of expire: when a key with an associated time to live (see the
EXPIRE command) must be deleted from memory.
3) Because of a side effect of a command that stores data on a key that may
already exist. For example the RENAME command may delete the old key
content when it is replaced with another one. Similarly SUNIONSTORE
or SORT with STORE option may delete existing keys. The SET command
itself removes any old content of the specified key in order to replace
it with the specified string.
4) During replication, when a replica performs a full resynchronization with
its master, the content of the whole database is removed in order to
load the RDB file just transferred.
In all the above cases the default is to delete objects in a blocking way,
like if DEL was called. However you can configure each case specifically
in order to instead release memory in a non-blocking way like if UNLINK
was called, using the following configuration directives:
APPEND ONLY MODE
By default Redis asynchronously dumps the dataset on disk. This mode is
good enough in many applications, but an issue with the Redis process or
a power outage may result into a few minutes of writes lost (depending on
the configured save points).
The Append Only File is an alternative persistence mode that provides
much better durability. For instance using the default data fsync policy
(see later in the config file) Redis can lose just one second of writes in a
dramatic event like a server power outage, or a single write if something
wrong with the Redis process itself happens, but the operating system is
still running correctly.
AOF and RDB persistence can be enabled at the same time without problems.
If the AOF is enabled on startup Redis will load the AOF, that is the file
with the better durability guarantees.
Please check http://redis.io/topics/persis... for more information.
The name of the append only file (default: "appendonly.aof")
The fsync() call tells the Operating System to actually write data on disk
instead of waiting for more data in the output buffer. Some OS will really flush
data on disk, some other OS will just try to do it ASAP.
Redis supports three different modes:
no: don't fsync, just let the OS flush the data when it wants. Faster.
always: fsync after every write to the append only log. Slow, Safest.
everysec: fsync only one time every second. Compromise.
The default is "everysec", as that's usually the right compromise between
speed and data safety. It's up to you to understand if you can relax this to
"no" that will let the operating system flush the output buffer when
it wants, for better performances (but if you can live with the idea of
some data loss consider the default persistence mode that's snapshotting),
or on the contrary, use "always" that's very slow but a bit safer than
More details please check the following article:
If unsure, use "everysec".
When the AOF fsync policy is set to always or everysec, and a background
saving process (a background save or AOF log background rewriting) is
performing a lot of I/O against the disk, in some Linux configurations
Redis may block too long on the fsync() call. Note that there is no fix for
this currently, as even performing fsync in a different thread will block
our synchronous write(2) call.
In order to mitigate this problem it's possible to use the following option
that will prevent fsync() from being called in the main process while a
BGSAVE or BGREWRITEAOF is in progress.
This means that while another child is saving, the durability of Redis is
the same as "appendfsync none". In practical terms, this means that it is
possible to lose up to 30 seconds of log in the worst scenario (with the
default Linux settings).
If you have latency problems turn this to "yes". Otherwise leave it as
"no" that is the safest pick from the point of view of durability.
Automatic rewrite of the append only file.
Redis is able to automatically rewrite the log file implicitly calling
BGREWRITEAOF when the AOF log size grows by the specified percentage.
This is how it works: Redis remembers the size of the AOF file after the
latest rewrite (if no rewrite has happened since the restart, the size of
the AOF at startup is used).
This base size is compared to the current size. If the current size is
bigger than the specified percentage, the rewrite is triggered. Also
you need to specify a minimal size for the AOF file to be rewritten, this
is useful to avoid rewriting the AOF file even if the percentage increase
is reached but it is still pretty small.
Specify a percentage of zero in order to disable the automatic AOF
An AOF file may be found to be truncated at the end during the Redis
startup process, when the AOF data gets loaded back into memory.
This may happen when the system where Redis is running
crashes, especially when an ext4 filesystem is mounted without the
data=ordered option (however this can't happen when Redis itself
crashes or aborts but the operating system still works correctly).
Redis can either exit with an error when this happens, or load as much
data as possible (the default now) and start if the AOF file is found
to be truncated at the end. The following option controls this behavior.
If aof-load-truncated is set to yes, a truncated AOF file is loaded and
the Redis server starts emitting a log to inform the user of the event.
Otherwise if the option is set to no, the server aborts with an error
and refuses to start. When the option is set to no, the user requires
to fix the AOF file using the "redis-check-aof" utility before to restart
Note that if the AOF file will be found to be corrupted in the middle
the server will still exit with an error. This option only applies when
Redis will try to read more data from the AOF file but not enough bytes
will be found.
When rewriting the AOF file, Redis is able to use an RDB preamble in the
AOF file for faster rewrites and recoveries. When this option is turned
on the rewritten AOF file is composed of two different stanzas:
When loading Redis recognizes that the AOF file starts with the "REDIS"
string and loads the prefixed RDB file, and continues loading the AOF
Max execution time of a Lua script in milliseconds.
If the maximum execution time is reached Redis will log that a script is
still in execution after the maximum allowed time and will start to
reply to queries with an error.
When a long running script exceeds the maximum execution time only the
SCRIPT KILL and SHUTDOWN NOSAVE commands are available. The first can be
used to stop a script that did not yet called write commands. The second
is the only way to shut down the server in the case a write command was
already issued by the script but the user doesn't want to wait for the natural
termination of the script.
Set it to 0 or a negative value for unlimited execution without warnings.
WARNING EXPERIMENTAL: Redis Cluster is considered to be stable code, however
in order to mark it as "mature" we need to wait for a non trivial percentage
of users to deploy it in production.
Normal Redis instances can't be part of a Redis Cluster; only nodes that are
started as cluster nodes can. In order to start a Redis instance as a
cluster node enable the cluster support uncommenting the following:
Every cluster node has a cluster configuration file. This file is not
intended to be edited by hand. It is created and updated by Redis nodes.
Every Redis Cluster node requires a different cluster configuration file.
Make sure that instances running in the same system do not have
overlapping cluster configuration file names.
Cluster node timeout is the amount of milliseconds a node must be unreachable
for it to be considered in failure state.
Most other internal time limits are multiple of the node timeout.
A replica of a failing master will avoid to start a failover if its data
looks too old.
There is no simple way for a replica to actually have an exact measure of
its "data age", so the following two checks are performed:
1) If there are multiple replicas able to failover, they exchange messages
in order to try to give an advantage to the replica with the best
replication offset (more data from the master processed).
Replicas will try to get their rank by offset, and apply to the start
of the failover a delay proportional to their rank.
2) Every single replica computes the time of the last interaction with
its master. This can be the last ping or command received (if the master
is still in the "connected" state), or the time that elapsed since the
disconnection with the master (if the replication link is currently down).
If the last interaction is too old, the replica will not try to failover
The point "2" can be tuned by user. Specifically a replica will not perform
the failover if, since the last interaction with the master, the time
elapsed is greater than:
(node-timeout * replica-validity-factor) + repl-ping-replica-period
So for example if node-timeout is 30 seconds, and the replica-validity-factor
is 10, and assuming a default repl-ping-replica-period of 10 seconds, the
replica will not try to failover if it was not able to talk with the master
for longer than 310 seconds.
A large replica-validity-factor may allow replicas with too old data to failover
a master, while a too small value may prevent the cluster from being able to
elect a replica at all.
For maximum availability, it is possible to set the replica-validity-factor
to a value of 0, which means, that replicas will always try to failover the
master regardless of the last time they interacted with the master.
(However they'll always try to apply a delay proportional to their
Zero is the only value able to guarantee that when all the partitions heal
the cluster will always be able to continue.
Cluster replicas are able to migrate to orphaned masters, that are masters
that are left without working replicas. This improves the cluster ability
to resist to failures as otherwise an orphaned master can't be failed over
in case of failure if it has no working replicas.
Replicas migrate to orphaned masters only if there are still at least a
given number of other working replicas for their old master. This number
is the "migration barrier". A migration barrier of 1 means that a replica
will migrate only if there is at least 1 other working replica for its master
and so forth. It usually reflects the number of replicas you want for every
master in your cluster.
Default is 1 (replicas migrate only if their masters remain with at least
one replica). To disable migration just set it to a very large value.
A value of 0 can be set but is useful only for debugging and dangerous
By default Redis Cluster nodes stop accepting queries if they detect there
is at least an hash slot uncovered (no available node is serving it).
This way if the cluster is partially down (for example a range of hash slots
are no longer covered) all the cluster becomes, eventually, unavailable.
It automatically returns available as soon as all the slots are covered again.
However sometimes you want the subset of the cluster which is working,
to continue to accept queries for the part of the key space that is still
covered. In order to do so, just set the cluster-require-full-coverage
option to no.
This option, when set to yes, prevents replicas from trying to failover its
master during master failures. However the master can still perform a
manual failover, if forced to do so.
This is useful in different scenarios, especially in the case of multiple
data center operations, where we want one side to never be promoted if not
in the case of a total DC failure.
In order to setup your cluster make sure to read the documentation
available at http://redis.io web site.
CLUSTER DOCKER/NAT support
In certain deployments, Redis Cluster nodes address discovery fails, because
addresses are NAT-ted or because ports are forwarded (the typical case is
Docker and other containers).
In order to make Redis Cluster working in such environments, a static
configuration where each node knows its public address is needed. The
following two options are used for this scope, and are:
Each instruct the node about its address, client port, and cluster message
bus port. The information is then published in the header of the bus packets
so that other nodes will be able to correctly map the address of the node
publishing the information.
If the above options are not used, the normal Redis Cluster auto-detection
will be used instead.
Note that when remapped, the bus port may not be at the fixed offset of
clients port + 10000, so you can specify any port and bus-port depending
on how they get remapped. If the bus-port is not set, a fixed offset of
10000 will be used as usually.
The Redis Slow Log is a system to log queries that exceeded a specified
execution time. The execution time does not include the I/O operations
like talking with the client, sending the reply and so forth,
but just the time needed to actually execute the command (this is the only
stage of command execution where the thread is blocked and can not serve
other requests in the meantime).
You can configure the slow log with two parameters: one tells Redis
what is the execution time, in microseconds, to exceed in order for the
command to get logged, and the other parameter is the length of the
slow log. When a new command is logged the oldest one is removed from the
queue of logged commands.
The following time is expressed in microseconds, so 1000000 is equivalent
to one second. Note that a negative number disables the slow log, while
a value of zero forces the logging of every command.
There is no limit to this length. Just be aware that it will consume memory.
You can reclaim memory used by the slow log with SLOWLOG RESET.
The Redis latency monitoring subsystem samples different operations
at runtime in order to collect data related to possible sources of
latency of a Redis instance.
Via the LATENCY command this information is available to the user that can
print graphs and obtain reports.
The system only logs operations that were performed in a time equal or
greater than the amount of milliseconds specified via the
latency-monitor-threshold configuration directive. When its value is set
to zero, the latency monitor is turned off.
By default latency monitoring is disabled since it is mostly not needed
if you don't have latency issues, and collecting data has a performance
impact, that while very small, can be measured under big load. Latency
monitoring can easily be enabled at runtime using the command
"CONFIG SET latency-monitor-threshold <milliseconds>" if needed.
Redis can notify Pub/Sub clients about events happening in the key space.
This feature is documented at http://redis.io/topics/notifi...
For instance if keyspace events notification is enabled, and a client
performs a DEL operation on key "foo" stored in the Database 0, two
messages will be published via Pub/Sub:
PUBLISH __keyspace@0__:foo del
PUBLISH __keyevent@0__:del foo
It is possible to select the events that Redis will notify among a set
of classes. Every class is identified by a single character:
K Keyspace events, published with keyspace@<db> prefix.
E Keyevent events, published with keyevent@<db> prefix.
g Generic commands (non-type specific) like DEL, EXPIRE, RENAME, ...
$ String commands
l List commands
s Set commands
h Hash commands
z Sorted set commands
x Expired events (events generated every time a key expires)
e Evicted events (events generated when a key is evicted for maxmemory)
A Alias for g$lshzxe, so that the "AKE" string means all the events.
The "notify-keyspace-events" takes as argument a string that is composed
of zero or multiple characters. The empty string means that notifications
Example: to enable list and generic events, from the point of view of the
event name, use:
Example 2: to get the stream of the expired keys subscribing to channel
name __keyevent@0__:expired use:
By default all notifications are disabled because most users don't need
this feature and the feature has some overhead. Note that if you don't
specify at least one of K or E, no events will be delivered.
Hashes are encoded using a memory efficient data structure when they have a
small number of entries, and the biggest entry does not exceed a given
threshold. These thresholds can be configured using the following directives.
Lists are also encoded in a special way to save a lot of space.
The number of entries allowed per internal list node can be specified
as a fixed maximum size or a maximum number of elements.
For a fixed maximum size, use -5 through -1, meaning:
-5: max size: 64 Kb <-- not recommended for normal workloads
-4: max size: 32 Kb <-- not recommended
-3: max size: 16 Kb <-- probably not recommended
-2: max size: 8 Kb <-- good
-1: max size: 4 Kb <-- good
Positive numbers mean store up to exactly that number of elements
per list node.
The highest performing option is usually -2 (8 Kb size) or -1 (4 Kb size),
but if your use case is unique, adjust the settings as necessary.
Lists may also be compressed.
Compress depth is the number of quicklist ziplist nodes from each side of
the list to exclude from compression. The head and tail of the list
are always uncompressed for fast push/pop operations. Settings are:
0: disable all list compression
1: depth 1 means "don't start compressing until after 1 node into the list,
going from either the head or tail"
[head], [tail] will always be uncompressed; inner nodes will compress.
2 here means: don't compress head or head->next or tail->prev or tail,
but compress all nodes between them.
Sets have a special encoding in just one case: when a set is composed
of just strings that happen to be integers in radix 10 in the range
of 64 bit signed integers.
The following configuration setting sets the limit in the size of the
set in order to use this special memory saving encoding.
Similarly to hashes and lists, sorted sets are also specially encoded in
order to save a lot of space. This encoding is only used when the length and
elements of a sorted set are below the following limits:
HyperLogLog sparse representation bytes limit. The limit includes the
16 bytes header. When an HyperLogLog using the sparse representation crosses
this limit, it is converted into the dense representation.
A value greater than 16000 is totally useless, since at that point the
dense representation is more memory efficient.
The suggested value is ~ 3000 in order to have the benefits of
the space efficient encoding without slowing down too much PFADD,
which is O(N) with the sparse encoding. The value can be raised to
~ 10000 when CPU is not a concern, but space is, and the data set is
composed of many HyperLogLogs with cardinality in the 0 - 15000 range.
Streams macro node max size / items. The stream data structure is a radix
tree of big nodes that encode multiple items inside. Using this configuration
it is possible to configure how big a single node can be in bytes, and the
maximum number of items it may contain before switching to a new node when
appending new stream entries. If any of the following settings are set to
zero, the limit is ignored, so for instance it is possible to set just a
max entires limit by setting max-bytes to 0 and max-entries to the desired
Active rehashing uses 1 millisecond every 100 milliseconds of CPU time in
order to help rehashing the main Redis hash table (the one mapping top-level
keys to values). The hash table implementation Redis uses (see dict.c)
performs a lazy rehashing: the more operation you run into a hash table
that is rehashing, the more rehashing "steps" are performed, so if the
server is idle the rehashing is never complete and some more memory is used
by the hash table.
The default is to use this millisecond 10 times every second in order to
actively rehash the main dictionaries, freeing memory when possible.
use "activerehashing no" if you have hard latency requirements and it is
not a good thing in your environment that Redis can reply from time to time
to queries with 2 milliseconds delay.
use "activerehashing yes" if you don't have such hard requirements but
want to free memory asap when possible.
The client output buffer limits can be used to force disconnection of clients
that are not reading data from the server fast enough for some reason (a
common reason is that a Pub/Sub client can't consume messages as fast as the
publisher can produce them).
The limit can be set differently for the three different classes of clients:
normal -> normal clients including MONITOR clients
replica -> replica clients
pubsub -> clients subscribed to at least one pubsub channel or pattern
The syntax of every client-output-buffer-limit directive is the following:
client-output-buffer-limit <class> <hard limit> <soft limit> <soft seconds>
A client is immediately disconnected once the hard limit is reached, or if
the soft limit is reached and remains reached for the specified number of
So for instance if the hard limit is 32 megabytes and the soft limit is
16 megabytes / 10 seconds, the client will get disconnected immediately
if the size of the output buffers reach 32 megabytes, but will also get
disconnected if the client reaches 16 megabytes and continuously overcomes
the limit for 10 seconds.
By default normal clients are not limited because they don't receive data
without asking (in a push way), but just after a request, so only
asynchronous clients may create a scenario where data is requested faster
than it can read.
Instead there is a default limit for pubsub and replica clients, since
subscribers and replicas receive data in a push fashion.
Both the hard or the soft limit can be disabled by setting them to zero.
client-output-buffer-limit normal 0 0 0
client-output-buffer-limit replica 256mb 64mb 60
client-output-buffer-limit pubsub 32mb 8mb 60
Client query buffers accumulate new commands. They are limited to a fixed
amount by default in order to avoid that a protocol desynchronization (for
instance due to a bug in the client) will lead to unbound memory usage in
the query buffer. However you can configure it here if you have very special
needs, such us huge multi/exec requests or alike.
In the Redis protocol, bulk requests, that are, elements representing single
strings, are normally limited ot 512 mb. However you can change this limit
Redis calls an internal function to perform many background tasks, like
closing connections of clients in timeout, purging expired keys that are
never requested, and so forth.
Not all tasks are performed with the same frequency, but Redis checks for
tasks to perform according to the specified "hz" value.
By default "hz" is set to 10. Raising the value will use more CPU when
Redis is idle, but at the same time will make Redis more responsive when
there are many keys expiring at the same time, and timeouts may be
handled with more precision.
The range is between 1 and 500, however a value over 100 is usually not
a good idea. Most users should use the default of 10 and raise this up to
100 only in environments where very low latency is required.
Normally it is useful to have an HZ value which is proportional to the
number of clients connected. This is useful in order, for instance, to
avoid too many clients are processed for each background task invocation
in order to avoid latency spikes.
Since the default HZ value by default is conservatively set to 10, Redis
offers, and enables by default, the ability to use an adaptive HZ value
which will temporary raise when there are many connected clients.
When dynamic HZ is enabled, the actual configured HZ will be used as
as a baseline, but multiples of the configured HZ value will be actually
used as needed once more clients are connected. In this way an idle
instance will use very little CPU time while a busy instance will be
When a child rewrites the AOF file, if the following option is enabled
the file will be fsync-ed every 32 MB of data generated. This is useful
in order to commit the file to the disk more incrementally and avoid
big latency spikes.
When redis saves RDB file, if the following option is enabled
the file will be fsync-ed every 32 MB of data generated. This is useful
in order to commit the file to the disk more incrementally and avoid
big latency spikes.