redis data types

Redis Data Type Summary

There are plenty of good resources on the internet, but I’m writing this up as study

Testing is done with redis-cli, but for real use I’d probably use an api library for the language

Overview

http://redis.io/topics/data-types-intro

Examples

http://redis.io/topics/data-types

Strings

Stores characters, numbers, etc. as values
No separate type on save (no distinction between numbers and strings)
Numbers can be stored too, and atomic counter operations like incr, incrby, decr, decrby are possible on them
incrby, decrby add or subtract a specific number, used like incrby "test_strings" 10

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# redis-cli
127.0.0.1:6379> set "test_strings" 1
OK
127.0.0.1:6379> get "test_strings"
"1"
127.0.0.1:6379> incr "test_strings"
(integer) 2
127.0.0.1:6379> get "test_strings"
"2"
127.0.0.1:6379>

Lists

Stores a list as the value
lrange: reads values, where -1 means fetch everything

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127.0.0.1:6379> lpush "test_lists" 1
127.0.0.1:6379> lpush test_lists 2
127.0.0.1:6379> lrange test_lists 0 -1
1) "2"
2) "1"
127.0.0.1:6379> rpush test_lists 3
(integer) 3
127.0.0.1:6379> lrange test_lists 0 -1
1) "2"
2) "1"
3) "3"

Seems like you could implement a queue with rpop

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127.0.0.1:6379> rpop test_lists
"3"
127.0.0.1:6379> lrange test_lists 0 -1
1) "2"
2) "1"

With rbpop it seems you could even implement sequential distributed work. Similar to rpop but if there’s no data it waits in a block state until data comes in

Sets

Holds the value as a set
Lists allow duplicates but sets don’t

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127.0.0.1:6379> sadd test_sets 1
(integer) 1
127.0.0.1:6379> smembers test_sets
1) "1"
127.0.0.1:6379> sadd test_sets 1 2 3 4
(integer) 3
127.0.0.1:6379> smembers test_sets
1) "1"
2) "2"
3) "3"
4) "4"

Hashes

Hashes hold a key/value list as the value

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127.0.0.1:6379> hset htest username hi
(integer) 1
127.0.0.1:6379> hset htest userpwd asdf
(integer) 1
127.0.0.1:6379> hget htest username
"hi"
127.0.0.1:6379> hgetall htest
1) "username"
2) "hi"
3) "userpwd"
4) "asdf"

hget returns (nil) if there’s no value

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127.0.0.1:6379> hget htest temp
(nil)

Changing the value for a hashkey

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127.0.0.1:6379> hget htest userpwd
"asdf"
127.0.0.1:6379> hset htest userpwd 1234
(integer) 0
127.0.0.1:6379> hget htest userpwd
"1234"

Sorted sets

Holds the value as a set
Like Sets, no duplicates
Stored together with a score, and sorted by score
Seems usable like a list, with the advantage of being sorted

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127.0.0.1:6379> zadd test_ssets 1 1
(integer) 1
127.0.0.1:6379> zadd test_ssets 2 2
(integer) 1
127.0.0.1:6379> zrange test_ssets 0 -1
1) "1"
2) "2"

Don’t use a string for the score

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127.0.0.1:6379> zadd test_ssets "a" 2
(error) ERR value is not a valid float

Since duplicates aren’t allowed, inserting the same value overwrites the existing data’s score and the order changes

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127.0.0.1:6379> zadd test_ssets "0" 2
(integer) 0
127.0.0.1:6379> zrange test_ssets 0 -1
1) "2"
2) "1"

Bitmaps

Stores bit values
Can store 2^32 (4.2 billion) bit values in 512MB
Seems good for storing boolean option values (like whether each member has viewed a notice)

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127.0.0.1:6379> setbit test_bits 0 1
(integer) 0
127.0.0.1:6379> getbit test_bits 0
(integer) 1
127.0.0.1:6379> setbit test_bits 0 0
(integer) 1
127.0.0.1:6379> getbit test_bits 0
(integer) 0