Redis Configuration file
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Redis configuration file example.
Note that in order to read the configuration file, Redis must be started with the file path as first argument:
# ./redis-server /path/to/redis.conf
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 => 1024*1024*1024 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.
# include /path/to/local.conf
# include /path/to/other.conf
Load modules at startup. If the server is not able to load modules
it will abort. It is possible to use multiple loadmodule directives.
# loadmodule /path/to/my_module.so
# loadmodule /path/to/other_module.so
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 "bind" directive.
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 sockets.
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
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.
# unixsocket /tmp/redis.sock
# unixsocketperm 700
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.
# syslog-enabled no
Specify the syslog identity.
# syslog-ident redis
Specify the syslog facility. Must be USER or between LOCAL0-LOCAL7.
# syslog-facility local0
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.
- 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.
- 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.
- 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.
# masterauth <master-password>
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:
- 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.
- 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:
- 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.
- 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.
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
# repl-ping-replica-period 10
The following option sets the replication timeout for:
- Bulk transfer I/O during SYNC, from the point of view of replica.
- Master timeout from the point of view of replicas (data, pings).
- 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
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.
# repl-backlog-ttl 3600
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:
# min-replicas-to-write 3
# min-replicas-max-lag 10
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.
# replica-announce-ip 18.104.22.168
# replica-announce-port 1234
Require clients to issue AUTH
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.
# requirepass foobared
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'.
# maxclients 10000
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 <bytes>
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 randomized algorithms.
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:
# maxmemory-policy noeviction
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.
# maxmemory-samples 5
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.
# replica-ignore-maxmemory yes
LAZYFREE-LAZY-EVICTION, LAZYFREE-LAZY-EXPIRE, LAZYFREE-LAZY-SERVER-DEL, REPLICA-LAZY-FLUSH
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 following scenarios:
- On eviction, because of the maxmemory and maxmemory policy configurations, in order to make room for new data, without going over the specified memory limit.
- Because of expire: when a key with an associated time to live (see the EXPIRE command) must be deleted from memory.
- 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.
- 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/persistence 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".
# appendfsync always
# appendfsync no
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 rewrite feature.
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 the server.
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:
[RDB file][AOF tail]
When loading Redis recognizes that the AOF file starts with the "REDIS" string and loads the prefixed RDB file, and continues loading the AOF tail.
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:
# cluster-enabled yes
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-config-file nodes-6379.conf
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.
# cluster-node-timeout 15000
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:
- 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.
- 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 at all.
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 offset rank).
Zero is the only value able to guarantee that when all the partitions heal the cluster will always be able to continue.
# cluster-replica-validity-factor 10
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 in production.
# cluster-migration-barrier 1
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.
# cluster-require-full-coverage yes
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.
# cluster-replica-no-failover no
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.
# cluster-announce-ip 10.1.1.5
# cluster-announce-port 6379
# cluster-announce-bus-port 6380
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/notifications
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@
- E Keyevent events, published with __keyevent@
- 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.
hash-max-ziplist-entries 512 more info
hash-max-ziplist-value 64 more info
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.
list-max-ziplist-size -2 more info
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: [head]->[next]->node->node->...->node->[prev]->[tail]
2 here means: don't compress head or head->next or tail->prev or tail, but compress all nodes between them.
- 3: [head]->[next]->[next]->node->node->...->node->[prev]->[prev]->[tail] etc.
list-compress-depth 0 more info
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.
set-max-intset-entries 512 more info
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:
zset-max-ziplist-entries 128 more info
zset-max-ziplist-value 64 more info
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.
hll-sparse-max-bytes 3000 more info
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
stream-node-max-bytes 4096 more info
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 seconds (continuously).
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.
# client-query-buffer-limit 1gb
In the Redis protocol, bulk requests, that are, elements representing single
strings, are normally limited ot 512 mb. However you can change this limit
# proto-max-bulk-len 512mb
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 more responsive.
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.
aof-rewrite-incremental-fsync yes more info
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.
rdb-save-incremental-fsync yes more info
Redis LFU eviction (see maxmemory setting) can be tuned. However it is a good
idea to start with the default settings and only change them after investigating
how to improve the performances and how the keys LFU change over time, which
is possible to inspect via the OBJECT FREQ command.
There are two tunable parameters in the Redis LFU implementation: the counter logarithm factor and the counter decay time. It is important to understand what the two parameters mean before changing them.
The LFU counter is just 8 bits per key, it's maximum value is 255, so Redis uses a probabilistic increment with logarithmic behavior. Given the value of the old counter, when a key is accessed, the counter is incremented in this way:
- A random number R between 0 and 1 is extracted.
- A probability P is calculated as 1/(old_value*lfu_log_factor+1).
- The counter is incremented only if R < P.
The default lfu-log-factor is 10. This is a table of how the frequency
counter changes with a different number of accesses with different
NOTE: The above table was obtained by running the following commands:
redis-benchmark -n 1000000 incr foo
redis-cli object freq foo
NOTE 2: The counter initial value is 5 in order to give new objects a chance to accumulate hits.
The counter decay time is the time, in minutes, that must elapse in order for the key counter to be divided by two (or decremented if it has a value less <= 10).
The default value for the lfu-decay-time is 1. A Special value of 0 means to decay the counter every time it happens to be scanned.
# lfu-log-factor 10
# lfu-decay-time 1
WARNING THIS FEATURE IS EXPERIMENTAL. However it was stress tested
even in production and manually tested by multiple engineers for some
What is active defragmentation?
Active (online) defragmentation allows a Redis server to compact the spaces left between small allocations and deallocations of data in memory, thus allowing to reclaim back memory.
Fragmentation is a natural process that happens with every allocator (but less so with Jemalloc, fortunately) and certain workloads. Normally a server restart is needed in order to lower the fragmentation, or at least to flush away all the data and create it again. However thanks to this feature implemented by Oran Agra for Redis 4.0 this process can happen at runtime in an "hot" way, while the server is running.
Basically when the fragmentation is over a certain level (see the configuration options below) Redis will start to create new copies of the values in contiguous memory regions by exploiting certain specific Jemalloc features (in order to understand if an allocation is causing fragmentation and to allocate it in a better place), and at the same time, will release the old copies of the data. This process, repeated incrementally for all the keys will cause the fragmentation to drop back to normal values.
Important things to understand:
- This feature is disabled by default, and only works if you compiled Redis to use the copy of Jemalloc we ship with the source code of Redis. This is the default with Linux builds.
- You never need to enable this feature if you don't have fragmentation issues.
- Once you experience fragmentation, you can enable this feature when needed with the command "CONFIG SET activedefrag yes".
The configuration parameters are able to fine tune the behavior of the
defragmentation process. If you are not sure about what they mean it is
a good idea to leave the defaults untouched.
Enabled active defragmentation
# activedefrag yes
Minimum amount of fragmentation waste to start active defrag
# active-defrag-ignore-bytes 100mb
Minimum percentage of fragmentation to start active defrag
# active-defrag-threshold-lower 10
Maximum percentage of fragmentation at which we use maximum effort
# active-defrag-threshold-upper 100
Minimal effort for defrag in CPU percentage
# active-defrag-cycle-min 5
Maximal effort for defrag in CPU percentage
# active-defrag-cycle-max 75
Maximum number of set/hash/zset/list fields that will be processed from
the main dictionary scan
# active-defrag-max-scan-fields 1000
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