Redis: Key Management

Redis is a key-based data structure storage system. This a key-value storage system, where we don’t have any table or rows or columns like a relational database.

The whole modeling/storing/retrieving of data depends on the key. So naming the key becomes very important.

Here is how to effectively name keys in a Redis database-

Redis Key Naming Convention

Empty string is a valid key name in Redis.

Key names are binary safe, so we can use binary sequences in the Redis key name.

Maximum allowed size of a key in Redis is 512MB.

Maximum number of keys that Redis can handle is 2^32.

Here are the things to consider while naming a Redis key-

The following commands are the most used and useful Redis commands for managing key and/or value.
Here we have discussed commands – KEYS, GET, SET, DEL, EXISTS, TYPE, EXPIRE, TTL, PERSIST.

Redis Command: KEYS – retrieve keys

Signature:

KEYS <pattern>

Usage:

Get the list of all keys in the database that matches the provided pattern(<pattern>)

Use with care in a production database. As, getting all the keys in a database with a huge dataset is an expensive task, and can harm the performance of the database in production.

Pattern Details:

The <pattern> in the command follows the Glob-style patterns. For example-

These patterns follow the Glob style.

Then patterns are case sensitive.

Use a backslash(\) to escape any special character.

Examples:

Check the example below-

127.0.0.1:6379> keys *
1) "a"
2) "site:domain"
3) "site:topic"
4) "somekey"
5) "site:name"

127.0.0.1:6379> keys site:*
1) "site:domain"
2) "site:topic"
3) "site:name"

127.0.0.1:6379> keys SIte*
(empty array)

127.0.0.1:6379> keys s???k*
1) "somekey"

Redis Command: GET – retrieve a value

Signature:

GET <key>

Usage:

Get value of the <key>.

Return Type:

Examples:

127.0.0.1:6379> get a
"dd"

127.0.0.1:6379> get wrongkey
(nil)

127.0.0.1:6379> get site:domain
"bigboxcode.com"

127.0.0.1:6379> get site:wrong
(nil)

Check Details of Redis GET Command

Redis Command: SET – set key/value

Signature:

Simple signature-

SET <key> <value>

Complete signature-

SET <key> <value> [NX | XX] [GET] [EX <seconds> | PX <milliseconds> | EXAT <unix-time-seconds> | PXAT <unix-time-milliseconds> | KEEPTTL]

Options:

Usage:

Set value for a key.

• If the key does not already exist, then it will be created and the value will be set.
• If the key already exists then the value is replaced with the newly provided value.
• If the key is already existing and has a TTL, then replace the TTL upon successful command execution.

Return Type:

Examples:

# set a key/value
127.0.0.1:6379> set firstkey "some value"
OK

# check the key/value
127.0.0.1:6379> get firstkey
"some value"

# set key/value with expire time of 10 seconds
127.0.0.1:6379> set secondkey "another value" ex 10
OK

# check within 10 seconds of setting, and the we will get the value
127.0.0.1:6379> get secondkey
"another value"

# check after 10 seconds of setting the value, and the value does not exist
127.0.0.1:6379> get secondkey
(nil)

# Try setting somekey and check if it not exists already
127.0.0.1:6379> set somekey newval nx
(nil)

127.0.0.1:6379> set differentkey newval nx
OK

# Set key/value only if that exists
127.0.0.1:6379> set somekey newval xx
OK

Check Details of Redis SET Command

Redis Command: DEL – destroy key/value

Signature:

DEL <key> [<anotehr_key> … ]

Usage:

Delete specific key or keys.

Return Type:

The number of keys that are deleted.

Examples:

# Set some vlaues
127.0.0.1:6379> set firstkey "value 123"
OK
127.0.0.1:6379> set secondkey "value 345"
OK
127.0.0.1:6379> set thirdkey "9876"
OK

# Delete firstkey. The command executes successfully
127.0.0.1:6379> del firstkey
(integer) 1

# Try to get firstkey, that returns error as the key no longer exists.
127.0.0.1:6379> get firstkey
(nil)

# Delete secondkey adn thirdkey. Both are deleted successfully.
127.0.0.1:6379> del secondkey thirdkey
(integer) 2

# Now try to delete secondkey again. It returns 0, s the secondkey does not exist anymore
127.0.0.1:6379> del secondkey
(integer) 0

A similar command is “UNLINK <key> [<another_key> … ]“. The Unlink command works like DEL, the difference is in the process.
Del deletes keys one by one, synchronously, and makes it a blocking command. That makes the memory reclaiming of the DEL command slower.
On the other hand, the UNLINK command is non-blocking, as the processing is done synchronously in different threads. In UNLINK the command the actual removal operation happens asynchronously, so the memory reclaiming is much faster than DEL.

Redis Command: EXISTS – check existence

Signature:

EXISTS <key> [<another_key> … ]

Usage:

Check if the key exists in keyspace or not.

Return Value:

Number(integer) of the keys that exist in the database.

If the same key name is passed twice and the key exists in the database, then 2 is returned. So the command does not consider the unique number of keys, which are passed.

Examples:

127.0.0.1:6379> keys *
1) "a"
2) "site:domain"
3) "b"
4) "site:topic"
5) "somekey"
6) "site:name"


127.0.0.1:6379> exists a
(integer) 1


127.0.0.1:6379> exists a b somekey
(integer) 3


127.0.0.1:6379> exists a a b somekey b
(integer) 5


127.0.0.1:6379> exists wrongkey
(integer) 0


127.0.0.1:6379> exists a wrongkey
(integer) 1

Redis Command: TYPE – check value type

Signature:

TYPE <key>

Usage:

Check the type of value saved in the key.

Return Value:

Examples:

127.0.0.1:6379> type somekey
string

127.0.0.1:6379> type hash1
hash

127.0.0.1:6379> type list1
list

127.0.0.1:6379> type wrongkey
none

Redis Command: RENAME– rename key

Signature:

RENAME <key> <new_key_name>

Usage:

Rename an existing key.

If the <new_key_name> already exists, then this command overrites the <new_key_name>. In the background, this RENAME command deletes the existing key <new_key_name> first and then creates a new entry with the <new_key_name>. So, if the value is large, then deleting and recreating the entry can cause performance issues.

Return Value:

Examples:

127.0.0.1:6379> set firstkey 99
OK

# Rename key
127.0.0.1:6379> rename firstkey changedkey
OK

# Try to rename the same key. We get error as the "firstkey" does not exist anymore
127.0.0.1:6379> rename firstkey changedkey
(error) ERR no such key


# Let's check another example

127.0.0.1:6379> set firstkey 100
OK

127.0.0.1:6379> set secondkey 200
OK

# Let's rename the firstkey to second key
127.0.0.1:6379> rename firstkey secondkey
OK

# After rename the firstkey deos not exist any more
127.0.0.1:6379> get firstkey
(nil)

# After rename the secondkey has the value(100) of first key
127.0.0.1:6379> get secondkey
"100"

A similar command is “RENAMEX <key> <new_key_name>“. In RENAMEX the key name is changed only if the key <new_key_name> does not exist. If the <new_key_name> already exists then the command returns Zero(0).

Redis Command: EXPIRE – set expiry time

Signature:

Simple use of the command-

EXPIRE <key> <seconds>

Full signature of the command-

EXPIRE <key> <seconds> [NX | XX | GT | LT]

Usage:

Set expiration time(timeout) for a key.

Options:

Return Value:

An integer value is returned-

Examples:

127.0.0.1:6379> set firstkey "first value"
OK

127.0.0.1:6379> expire firstkey 10
(integer) 1

127.0.0.1:6379> ttl firstkey
(integer) 4

127.0.0.1:6379> set firstkey "first value"
OK

127.0.0.1:6379> expire firstkey 20
(integer) 1

127.0.0.1:6379> expire firstkey 2 XX
(integer) 1

127.0.0.1:6379> expire firstkey 200 LT
(integer) 1

127.0.0.1:6379> ttl firstkey
(integer) 194

A similar command is “PEXPIRE<key> <milliseconds> [NX|XX|GT|LT]“. In the PEXPIRE command, we set the expiry time in milliseconds.

Another similar command is “EXPIREAT<key> <unix_time_in_seconds> [NX|XX|GT|LT]“. In the EXPIREAT command, we set an absolute UNIX timestamp (seconds since Jan 1, 1970) for when the key should expire.

Another similar command is “PEXPIREAT<key> <unix_time_in_milliseconds> [NX|XX|GT|LT]“. In the PEXPIREAT command, we set an absolute UNIX timestamp (milliseconds since Jan 1, 1970) for when the key should expire.

Redis Command: TTL – get remaining time

Signature:

TTL <key>

Usage:

Get the remaining time for the key expiry timeout, in seconds.

Return Value:

An integer value is returned-

Examples:

#set value with expiery time with 20 seconds
127.0.0.1:6379> set firstkey "somevalue" ex 20
OK

# check TTL
127.0.0.1:6379> ttl firstkey
(integer) 15

127.0.0.1:6379> ttl firstkey
(integer) 10

127.0.0.1:6379> ttl firstkey
(integer) 8

127.0.0.1:6379> ttl firstkey
(integer) 2

127.0.0.1:6379> ttl firstkey
(integer) 1

# TTL response when key is removed for timeout
127.0.0.1:6379> ttl firstkey
(integer) -2

# set the value without any TTL
127.0.0.1:6379> set firstkey "some value"
OK

# response when no TTL is associated
127.0.0.1:6379> ttl firstkey
(integer) -1

A similar command is “PTTL <key>“. The PTTL command returns the remaining time in milliseconds.

Redis Command: PERSIST – remove timeout

Signature:

PERSIST <key>

Usage:

Remove the timeout from the key. This command makes the key to persist with no more timeout.

Return Value:

An integer value is returned-

Examples:

# Set value with 200 seconds timeout
127.0.0.1:6379> set firstkey "some value" ex 200
OK

# Check the ttl
127.0.0.1:6379> ttl firstkey
(integer) 196

# Persist to remove the timeout
127.0.0.1:6379> persist firstkey
(integer) 1

# Check the ttl again. -1 is returned to indicate that, it does not have any expiry associated
127.0.0.1:6379> ttl firstkey
(integer) -1

127.0.0.1:6379> set firstkey 99
OK

# Then if we try to persist again then return value is 0 as not expiery time is associated with it
127.0.0.1:6379> persist firstkey
(integer) 0

# Let's try to persist a non existing key, 0 is returned
127.0.0.1:6379> persist wrongkey
(integer) 0