环境
win10

版本
21H1

虚拟机
Hyper-V

Linux版本
CentOS 8

Redis版本
6.0.6

手动启动(./redis-server redis.conf)无报错，能正常启动
使用systemctl start redis.service 报错
Job for redis.service failed because a timeout was exceeded.
See "systemctl status redis.service" and "journalctl -xe" for details.

service配置

Redis配置文件内容

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 => 102410241024 bytes

units are case insensitive so 1GB 1Gb 1gB are all the same.

################################## INCLUDES ###################################

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

################################## MODULES #####################################

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

################################## NETWORK #####################################

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.

Examples:

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

is running).

IF YOU ARE SURE YOU WANT YOUR INSTANCE TO LISTEN TO ALL THE INTERFACES

JUST COMMENT THE FOLLOWING LINE.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

bind 127.0.0.1

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.

protected-mode yes

Accept connections on the specified port, default is 6379 (IANA #815344).

If port 0 is specified Redis will not listen on a TCP socket.

port 6379

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.

tcp-backlog 511

Unix socket.

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)

timeout 0

TCP keepalive.

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.

tcp-keepalive 300

################################# TLS/SSL #####################################

By default, TLS/SSL is disabled. To enable it, the "tls-port" configuration

directive can be used to define TLS-listening ports. To enable TLS on the

default port, use:

port 0

tls-port 6379

Configure a X.509 certificate and private key to use for authenticating the

server to connected clients, masters or cluster peers. These files should be

PEM formatted.

tls-cert-file redis.crt

tls-key-file redis.key

Configure a DH parameters file to enable Diffie-Hellman (DH) key exchange:

tls-dh-params-file redis.dh

Configure a CA certificate(s) bundle or directory to authenticate TLS/SSL

clients and peers. Redis requires an explicit configuration of at least one

of these, and will not implicitly use the system wide configuration.

tls-ca-cert-file ca.crt

tls-ca-cert-dir /etc/ssl/certs

By default, clients (including replica servers) on a TLS port are required

to authenticate using valid client side certificates.

It is possible to disable authentication using this directive.

tls-auth-clients no

By default, a Redis replica does not attempt to establish a TLS connection

with its master.

Use the following directive to enable TLS on replication links.

tls-replication yes

By default, the Redis Cluster bus uses a plain TCP connection. To enable

TLS for the bus protocol, use the following directive:

tls-cluster yes

Explicitly specify TLS versions to support. Allowed values are case insensitive

and include "TLSv1", "TLSv1.1", "TLSv1.2", "TLSv1.3" (OpenSSL >= 1.1.1) or

any combination. To enable only TLSv1.2 and TLSv1.3, use:

tls-protocols "TLSv1.2 TLSv1.3"

Configure allowed ciphers. See the ciphers(1ssl) manpage for more information

about the syntax of this string.

Note: this configuration applies only to <= TLSv1.2.

tls-ciphers DEFAULT:!MEDIUM

Configure allowed TLSv1.3 ciphersuites. See the ciphers(1ssl) manpage for more

information about the syntax of this string, and specifically for TLSv1.3

ciphersuites.

tls-ciphersuites TLS_CHACHA20_POLY1305_SHA256

When choosing a cipher, use the server's preference instead of the client

preference. By default, the server follows the client's preference.

tls-prefer-server-ciphers yes

By default, TLS session caching is enabled to allow faster and less expensive

reconnections by clients that support it. Use the following directive to disable

caching.

tls-session-caching no

Change the default number of TLS sessions cached. A zero value sets the cache

to unlimited size. The default size is 20480.

tls-session-cache-size 5000

Change the default timeout of cached TLS sessions. The default timeout is 300

seconds.

tls-session-cache-timeout 60

################################# GENERAL #####################################

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.

daemonize no

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.

supervised systemd

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.

pidfile /var/run/redis_6379.pid

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)

loglevel notice

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

logfile ""

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

databases 16

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.

always-show-logo yes

################################ SNAPSHOTTING ################################

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 ""

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.

stop-writes-on-bgsave-error yes

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.

rdbcompression yes

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.

rdbchecksum yes

The filename where to dump the DB

dbfilename dump.rdb

Remove RDB files used by replication in instances without persistence

enabled. By default this option is disabled, however there are environments

where for regulations or other security concerns, RDB files persisted on

disk by masters in order to feed replicas, or stored on disk by replicas

in order to load them for the initial synchronization, should be deleted

ASAP. Note that this option ONLY WORKS in instances that have both AOF

and RDB persistence disabled, otherwise is completely ignored.

An alternative (and sometimes better) way to obtain the same effect is

to use diskless replication on both master and replicas instances. However

in the case of replicas, diskless is not always an option.

rdb-del-sync-files no

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.

dir ./

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

Master-Replica replication. Use replicaof to make a Redis instance a copy of

another Redis server. A few things to understand ASAP about Redis replication.

+------------------+ +---------------+

| Master | ---> | Replica |

| (receive writes) | | (exact copy) |

+------------------+ +---------------+

1) Redis replication is asynchronous, but you can configure a master to

stop accepting writes if it appears to be not connected with at least

a given number of replicas.

2) Redis replicas are able to perform a partial resynchronization with the

master if the replication link is lost for a relatively small amount of

time. You may want to configure the replication backlog size (see the next

sections of this file) with a sensible value depending on your needs.

3) Replication is automatic and does not need user intervention. After a

network partition replicas automatically try to reconnect to masters

and resynchronize with them.

replicaof <masterip> <masterport>

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>

However this is not enough if you are using Redis ACLs (for Redis version

6 or greater), and the default user is not capable of running the PSYNC

command and/or other commands needed for replication. In this case it's

better to configure a special user to use with replication, and specify the

masteruser configuration as such:

masteruser <username>

When masteruser is specified, the replica will authenticate against its

master using the new AUTH form: AUTH <username> <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:

1) if replica-serve-stale-data is set to 'yes' (the default) the replica will

still reply to client requests, possibly with out of date data, or the

data set may just be empty if this is the first synchronization.

2) if replica-serve-stale-data is set to 'no' the replica will reply with

an error "SYNC with master in progress" to all the kind of commands

but to INFO, replicaOF, AUTH, PING, SHUTDOWN, REPLCONF, ROLE, CONFIG,

SUBSCRIBE, UNSUBSCRIBE, PSUBSCRIBE, PUNSUBSCRIBE, PUBLISH, PUBSUB,

COMMAND, POST, HOST: and LATENCY.

replica-serve-stale-data yes

You can configure a replica instance to accept writes or not. Writing against

a replica instance may be useful to store some ephemeral data (because data

written on a replica will be easily deleted after resync with the master) but

may also cause problems if clients are writing to it because of a

misconfiguration.

Since Redis 2.6 by default replicas are read-only.

Note: read only replicas are not designed to be exposed to untrusted clients

on the internet. It's just a protection layer against misuse of the instance.

Still a read only replica exports by default all the administrative commands

such as CONFIG, DEBUG, and so forth. To a limited extent you can improve

security of read only replicas using 'rename-command' to shadow all the

administrative / dangerous commands.

replica-read-only yes

Replication SYNC strategy: disk or socket.

New replicas and reconnecting replicas that are not able to continue the

replication process just receiving differences, need to do what is called a

"full synchronization". An RDB file is transmitted from the master to the

replicas.

The transmission can happen in two different ways:

1) Disk-backed: The Redis master creates a new process that writes the RDB

file on disk. Later the file is transferred by the parent

process to the replicas incrementally.

2) Diskless: The Redis master creates a new process that directly writes the

RDB file to replica sockets, without touching the disk at all.

With disk-backed replication, while the RDB file is generated, more replicas

can be queued and served with the RDB file as soon as the current child

producing the RDB file finishes its work. With diskless replication instead

once the transfer starts, new replicas arriving will be queued and a new

transfer will start when the current one terminates.

When diskless replication is used, the master waits a configurable amount of

time (in seconds) before starting the transfer in the hope that multiple

replicas will arrive and the transfer can be parallelized.

With slow disks and fast (large bandwidth) networks, diskless replication

works better.

repl-diskless-sync no

When diskless replication is enabled, it is possible to configure the delay

the server waits in order to spawn the child that transfers the RDB via socket

to the replicas.

This is important since once the transfer starts, it is not possible to serve

new replicas arriving, that will be queued for the next RDB transfer, so the

server waits a delay in order to let more replicas arrive.

The delay is specified in seconds, and by default is 5 seconds. To disable

it entirely just set it to 0 seconds and the transfer will start ASAP.

repl-diskless-sync-delay 5

-----------------------------------------------------------------------------

WARNING: RDB diskless load is experimental. Since in this setup the replica

does not immediately store an RDB on disk, it may cause data loss during

failovers. RDB diskless load + Redis modules not handling I/O reads may also

cause Redis to abort in case of I/O errors during the initial synchronization

stage with the master. Use only if your do what you are doing.

-----------------------------------------------------------------------------

Replica can load the RDB it reads from the replication link directly from the

socket, or store the RDB to a file and read that file after it was completely

recived from the master.

In many cases the disk is slower than the network, and storing and loading

the RDB file may increase replication time (and even increase the master's

Copy on Write memory and salve buffers).

However, parsing the RDB file directly from the socket may mean that we have

to flush the contents of the current database before the full rdb was

received. For this reason we have the following options:

"disabled" - Don't use diskless load (store the rdb file to the disk first)

"on-empty-db" - Use diskless load only when it is completely safe.

"swapdb" - Keep a copy of the current db contents in RAM while parsing

the data directly from the socket. note that this requires

sufficient memory, if you don't have it, you risk an OOM kill.

repl-diskless-load disabled

Replicas send PINGs to server in a predefined interval. It's possible to

change this interval with the repl_ping_replica_period option. The default

value is 10 seconds.

repl-ping-replica-period 10

The following option sets the replication timeout for:

1) Bulk transfer I/O during SYNC, from the point of view of replica.

2) Master timeout from the point of view of replicas (data, pings).

3) Replica timeout from the point of view of masters (REPLCONF ACK pings).

It is important to make sure that this value is greater than the value

specified for repl-ping-replica-period otherwise a timeout will be detected

every time there is low traffic between the master and the replica.

repl-timeout 60

Disable TCP_NODELAY on the replica socket after SYNC?

If you select "yes" Redis will use a smaller number of TCP packets and

less bandwidth to send data to replicas. But this can add a delay for

the data to appear on the replica side, up to 40 milliseconds with

Linux kernels using a default configuration.

If you select "no" the delay for data to appear on the replica side will

be reduced but more bandwidth will be used for replication.

By default we optimize for low latency, but in very high traffic conditions

or when the master and replicas are many hops away, turning this to "yes" may

be a good idea.

repl-disable-tcp-nodelay no

Set the replication backlog size. The backlog is a buffer that accumulates

replica data when replicas are disconnected for some time, so that when a

replica wants to reconnect again, often a full resync is not needed, but a

partial resync is enough, just passing the portion of data the replica

missed while disconnected.

The bigger the replication backlog, the longer the time the replica can be

disconnected and later be able to perform a partial resynchronization.

The backlog is only allocated once there is at least a replica connected.

repl-backlog-size 1mb

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.

replica-priority 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 5.5.5.5

replica-announce-port 1234

############################### KEYS TRACKING #################################

Redis implements server assisted support for client side caching of values.

This is implemented using an invalidation table that remembers, using

16 millions of slots, what clients may have certain subsets of keys. In turn

this is used in order to send invalidation messages to clients. Please

to understand more about the feature check this page:

https://redis.io/topics/client-side-caching

When tracking is enabled for a client, all the read only queries are assumed

to be cached: this will force Redis to store information in the invalidation

table. When keys are modified, such information is flushed away, and

invalidation messages are sent to the clients. However if the workload is

heavily dominated by reads, Redis could use more and more memory in order

to track the keys fetched by many clients.

For this reason it is possible to configure a maximum fill value for the

invalidation table. By default it is set to 1M of keys, and once this limit

is reached, Redis will start to evict keys in the invalidation table

even if they were not modified, just to reclaim memory: this will in turn

force the clients to invalidate the cached values. Basically the table

maximum size is a trade off between the memory you want to spend server

side to track information about who cached what, and the ability of clients

to retain cached objects in memory.

If you set the value to 0, it means there are no limits, and Redis will

retain as many keys as needed in the invalidation table.

In the "stats" INFO section, you can find information about the number of

keys in the invalidation table at every given moment.

Note: when key tracking is used in broadcasting mode, no memory is used

in the server side so this setting is useless.

tracking-table-max-keys 1000000

################################## SECURITY ###################################

Warning: since Redis is pretty fast an outside user can try up to

1 million passwords per second against a modern box. This means that you

should use very strong passwords, otherwise they will be very easy to break.

Note that because the password is really a shared secret between the client

and the server, and should not be memorized by any human, the password

can be easily a long string from /dev/urandom or whatever, so by using a

long and unguessable password no brute force attack will be possible.

Redis ACL users are defined in the following format:

user <username> ... acl rules ...

For example:

user worker +@list +@connection ~jobs:* on >ffa9203c493aa99

The special username "default" is used for new connections. If this user

has the "nopass" rule, then new connections will be immediately authenticated

as the "default" user without the need of any password provided via the

AUTH command. Otherwise if the "default" user is not flagged with "nopass"

the connections will start in not authenticated state, and will require

AUTH (or the HELLO command AUTH option) in order to be authenticated and

start to work.

The ACL rules that describe what an user can do are the following:

on Enable the user: it is possible to authenticate as this user.

off Disable the user: it's no longer possible to authenticate

with this user, however the already authenticated connections

will still work.

+<command> Allow the execution of that command

-<command> Disallow the execution of that command

+@<category> Allow the execution of all the commands in such category

with valid categories are like @admin, @set, @sortedset, ...

and so forth, see the full list in the server.c file where

the Redis command table is described and defined.

The special category @all means all the commands, but currently

present in the server, and that will be loaded in the future

via modules.

+<command>|subcommand Allow a specific subcommand of an otherwise

disabled command. Note that this form is not

allowed as negative like -DEBUG|SEGFAULT, but

only additive starting with "+".

allcommands Alias for +@all. Note that it implies the ability to execute

all the future commands loaded via the modules system.

nocommands Alias for -@all.

~<pattern> Add a pattern of keys that can be mentioned as part of

commands. For instance ~* allows all the keys. The pattern

is a glob-style pattern like the one of KEYS.

It is possible to specify multiple patterns.

allkeys Alias for ~*

resetkeys Flush the list of allowed keys patterns.

><password> Add this passowrd to the list of valid password for the user.

For example >mypass will add "mypass" to the list.

This directive clears the "nopass" flag (see later).

<<password> Remove this password from the list of valid passwords.

nopass All the set passwords of the user are removed, and the user

is flagged as requiring no password: it means that every

password will work against this user. If this directive is

used for the default user, every new connection will be

immediately authenticated with the default user without

any explicit AUTH command required. Note that the "resetpass"

directive will clear this condition.

resetpass Flush the list of allowed passwords. Moreover removes the

"nopass" status. After "resetpass" the user has no associated

passwords and there is no way to authenticate without adding

some password (or setting it as "nopass" later).

reset Performs the following actions: resetpass, resetkeys, off,

-@all. The user returns to the same state it has immediately

after its creation.

ACL rules can be specified in any order: for instance you can start with

passwords, then flags, or key patterns. However note that the additive

and subtractive rules will CHANGE MEANING depending on the ordering.

For instance see the following example:

user alice on +@all -DEBUG ~* >somepassword

This will allow "alice" to use all the commands with the exception of the

DEBUG command, since +@all added all the commands to the set of the commands

alice can use, and later DEBUG was removed. However if we invert the order

of two ACL rules the result will be different:

user alice on -DEBUG +@all ~* >somepassword

Now DEBUG was removed when alice had yet no commands in the set of allowed

commands, later all the commands are added, so the user will be able to

execute everything.

Basically ACL rules are processed left-to-right.

For more information about ACL configuration please refer to

the Redis web site at https://redis.io/topics/acl

ACL LOG

The ACL Log tracks failed commands and authentication events associated

with ACLs. The ACL Log is useful to troubleshoot failed commands blocked

by ACLs. The ACL Log is stored in memory. You can reclaim memory with

ACL LOG RESET. Define the maximum entry length of the ACL Log below.

acllog-max-len 128

Using an external ACL file

Instead of configuring users here in this file, it is possible to use

a stand-alone file just listing users. The two methods cannot be mixed:

if you configure users here and at the same time you activate the exteranl

ACL file, the server will refuse to start.

The format of the external ACL user file is exactly the same as the

format that is used inside redis.conf to describe users.

aclfile /etc/redis/users.acl

IMPORTANT NOTE: starting with Redis 6 "requirepass" is just a compatiblity

layer on top of the new ACL system. The option effect will be just setting

the password for the default user. Clients will still authenticate using

AUTH <password> as usually, or more explicitly with AUTH default <password>

if they follow the new protocol: both will work.

requirepass foobared

Command renaming (DEPRECATED).

------------------------------------------------------------------------

WARNING: avoid using this option if possible. Instead use ACLs to remove

commands from the default user, and put them only in some admin user you

create for administrative purposes.

------------------------------------------------------------------------

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.

Example:

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.

################################### CLIENTS ####################################

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'.

IMPORTANT: When Redis Cluster is used, the max number of connections is also

shared with the cluster bus: every node in the cluster will use two

connections, one incoming and another outgoing. It is important to size the

limit accordingly in case of very large clusters.

maxclients 10000

############################## MEMORY MANAGEMENT ################################

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 128MB

MAXMEMORY POLICY: how Redis will select what to remove when maxmemory

is reached. You can select one from the following behaviors:

volatile-lru -> Evict using approximated LRU, only keys with an expire set.

allkeys-lru -> Evict any key using approximated LRU.

volatile-lfu -> Evict using approximated LFU, only keys with an expire set.

allkeys-lfu -> Evict any key using approximated LFU.

volatile-random -> Remove a random key having 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

configuration directive.

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

Redis reclaims expired keys in two ways: upon access when those keys are

found to be expired, and also in background, in what is called the

"active expire key". The key space is slowly and interactively scanned

looking for expired keys to reclaim, so that it is possible to free memory

of keys that are expired and will never be accessed again in a short time.

The default effort of the expire cycle will try to avoid having more than

ten percent of expired keys still in memory, and will try to avoid consuming

more than 25% of total memory and to add latency to the system. However

it is possible to increase the expire "effort" that is normally set to

"1", to a greater value, up to the value "10". At its maximum value the

system will use more CPU, longer cycles (and technically may introduce

more latency), and will tollerate less already expired keys still present

in the system. It's a tradeoff betweeen memory, CPU and latecy.

active-expire-effort 1

############################# LAZY FREEING ####################################

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:

1) 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.

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.

lazyfree-lazy-eviction no
lazyfree-lazy-expire no
lazyfree-lazy-server-del no
replica-lazy-flush no

It is also possible, for the case when to replace the user code DEL calls

with UNLINK calls is not easy, to modify the default behavior of the DEL

command to act exactly like UNLINK, using the following configuration

directive:

lazyfree-lazy-user-del no

################################ THREADED I/O #################################

Redis is mostly single threaded, however there are certain threaded

operations such as UNLINK, slow I/O accesses and other things that are

performed on side threads.

Now it is also possible to handle Redis clients socket reads and writes

in different I/O threads. Since especially writing is so slow, normally

Redis users use pipelining in order to speedup the Redis performances per

core, and spawn multiple instances in order to scale more. Using I/O

threads it is possible to easily speedup two times Redis without resorting

to pipelining nor sharding of the instance.

By default threading is disabled, we suggest enabling it only in machines

that have at least 4 or more cores, leaving at least one spare core.

Using more than 8 threads is unlikely to help much. We also recommend using

threaded I/O only if you actually have performance problems, with Redis

instances being able to use a quite big percentage of CPU time, otherwise

there is no point in using this feature.

So for instance if you have a four cores boxes, try to use 2 or 3 I/O

threads, if you have a 8 cores, try to use 6 threads. In order to

enable I/O threads use the following configuration directive:

io-threads 4

Setting io-threads to 1 will just use the main thread as usually.

When I/O threads are enabled, we only use threads for writes, that is

to thread the write(2) syscall and transfer the client buffers to the

socket. However it is also possible to enable threading of reads and

protocol parsing using the following configuration directive, by setting

it to yes:

io-threads-do-reads no

Usually threading reads doesn't help much.

NOTE 1: This configuration directive cannot be changed at runtime via

CONFIG SET. Aso this feature currently does not work when SSL is

enabled.

NOTE 2: If you want to test the Redis speedup using redis-benchmark, make

sure you also run the benchmark itself in threaded mode, using the

--threads option to match the number of Redis theads, otherwise you'll not

be able to notice the improvements.

############################## 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.

appendonly no

The name of the append only file (default: "appendonly.aof")

appendfilename "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

everysec.

More details please check the following article:

http://antirez.com/post/redis-persistence-demystified.html

If unsure, use "everysec".

appendfsync always

appendfsync everysec

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.

no-appendfsync-on-rewrite no

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.

auto-aof-rewrite-percentage 100
auto-aof-rewrite-min-size 64mb

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.

aof-load-truncated yes

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.

aof-use-rdb-preamble yes

################################ LUA SCRIPTING ###############################

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.

lua-time-limit 5000

################################ REDIS CLUSTER ###############################

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:

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

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

This option, when set to yes, allows nodes to serve read traffic while the

the cluster is in a down state, as long as it believes it owns the slots.

This is useful for two cases. The first case is for when an application

doesn't require consistency of data during node failures or network partitions.

One example of this is a cache, where as long as the node has the data it

should be able to serve it.

The second use case is for configurations that don't meet the recommended

three shards but want to enable cluster mode and scale later. A

master outage in a 1 or 2 shard configuration causes a read/write outage to the

entire cluster without this option set, with it set there is only a write outage.

Without a quorum of masters, slot ownership will not change automatically.

cluster-allow-reads-when-down 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:

* cluster-announce-ip

* cluster-announce-port

* cluster-announce-bus-port

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.

Example:

cluster-announce-ip 10.1.1.5

cluster-announce-port 6379

cluster-announce-bus-port 6380

################################## SLOW LOG ###################################

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.

slowlog-log-slower-than 10000

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.

slowlog-max-len 128

################################ LATENCY MONITOR ##############################

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.

latency-monitor-threshold 0

############################# EVENT NOTIFICATION ##############################

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@<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)

t Stream commands

m Key-miss events (Note: It is not included in the 'A' class)

A Alias for g$lshzxet, so that the "AKE" string means all the events

(Except key-miss events which are excluded from 'A' due to their

unique nature).

The "notify-keyspace-events" takes as argument a string that is composed

of zero or multiple characters. The empty string means that notifications

are disabled.

Example: to enable list and generic events, from the point of view of the

event name, use:

notify-keyspace-events Elg

Example 2: to get the stream of the expired keys subscribing to channel

name keyevent@0:expired use:

notify-keyspace-events Ex

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.

notify-keyspace-events ""

############################### GOPHER SERVER #################################

Redis contains an implementation of the Gopher protocol, as specified in

the RFC 1436 (https://www.ietf.org/rfc/rfc1436.txt).

The Gopher protocol was very popular in the late '90s. It is an alternative

to the web, and the implementation both server and client side is so simple

that the Redis server has just 100 lines of code in order to implement this

support.

What do you do with Gopher nowadays? Well Gopher never really died, and

lately there is a movement in order for the Gopher more hierarchical content

composed of just plain text documents to be resurrected. Some want a simpler

internet, others believe that the mainstream internet became too much

controlled, and it's cool to create an alternative space for people that

want a bit of fresh air.

Anyway for the 10nth birthday of the Redis, we gave it the Gopher protocol

as a gift.

--- HOW IT WORKS? ---

The Redis Gopher support uses the inline protocol of Redis, and specifically

two kind of inline requests that were anyway illegal: an empty request

or any request that starts with "/" (there are no Redis commands starting

with such a slash). Normal RESP2/RESP3 requests are completely out of the

path of the Gopher protocol implementation and are served as usually as well.

If you open a connection to Redis when Gopher is enabled and send it

a string like "/foo", if there is a key named "/foo" it is served via the

Gopher protocol.

In order to create a real Gopher "hole" (the name of a Gopher site in Gopher

talking), you likely need a script like the following:

https://github.com/antirez/gopher2redis

--- SECURITY WARNING ---

If you plan to put Redis on the internet in a publicly accessible address

to server Gopher pages MAKE SURE TO SET A PASSWORD to the instance.

Once a password is set:

1. The Gopher server (when enabled, not by default) will still serve

content via Gopher.

2. However other commands cannot be called before the client will

authenticate.

So use the 'requirepass' option to protect your instance.

To enable Gopher support uncomment the following line and set

the option from no (the default) to yes.

gopher-enabled no

############################### ADVANCED CONFIG ###############################

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
hash-max-ziplist-value 64

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

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"

So: [head]->node->node->...->node->[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

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

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
zset-max-ziplist-value 64

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

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

value.

stream-node-max-bytes 4096
stream-node-max-entries 100

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.

If unsure:

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.

activerehashing yes

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

here.

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.

hz 10

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 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.

dynamic-hz yes

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

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

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:

1. A random number R between 0 and 1 is extracted.

2. A probability P is calculated as 1/(old_value*lfu_log_factor+1).

3. 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

logarithmic factors:

+--------+------------+------------+------------+------------+------------+

| factor | 100 hits | 1000 hits | 100K hits | 1M hits | 10M hits |

+--------+------------+------------+------------+------------+------------+

| 0 | 104 | 255 | 255 | 255 | 255 |

+--------+------------+------------+------------+------------+------------+

| 1 | 18 | 49 | 255 | 255 | 255 |

+--------+------------+------------+------------+------------+------------+

| 10 | 10 | 18 | 142 | 255 | 255 |

+--------+------------+------------+------------+------------+------------+

| 100 | 8 | 11 | 49 | 143 | 255 |

+--------+------------+------------+------------+------------+------------+

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

########################### ACTIVE DEFRAGMENTATION #######################

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:

1. 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.

2. You never need to enable this feature if you don't have fragmentation

issues.

3. 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 no

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, to be used when the lower

threshold is reached

active-defrag-cycle-min 1

Maximal effort for defrag in CPU percentage, to be used when the upper

threshold is reached

active-defrag-cycle-max 25

Maximum number of set/hash/zset/list fields that will be processed from

the main dictionary scan

active-defrag-max-scan-fields 1000

Jemalloc background thread for purging will be enabled by default

jemalloc-bg-thread yes

It is possible to pin different threads and processes of Redis to specific

CPUs in your system, in order to maximize the performances of the server.

This is useful both in order to pin different Redis threads in different

CPUs, but also in order to make sure that multiple Redis instances running

in the same host will be pinned to different CPUs.

Normally you can do this using the "taskset" command, however it is also

possible to this via Redis configuration directly, both in Linux and FreeBSD.

You can pin the server/IO threads, bio threads, aof rewrite child process, and

the bgsave child process. The syntax to specify the cpu list is the same as

the taskset command:

Set redis server/io threads to cpu affinity 0,2,4,6:

server_cpulist 0-7:2

Set bio threads to cpu affinity 1,3:

bio_cpulist 1,3

Set aof rewrite child process to cpu affinity 8,9,10,11:

aof_rewrite_cpulist 8-11

Set bgsave child process to cpu affinity 1,10,11

bgsave_cpulist 1,10-11