Redis special data type bitmap

brief introduction ：

In development , This may happen ： Need to count some information of users , If active or inactive , Log in or not log in ; If you need to record the user's clock in for one year , It was 1, I didn't punch in 0, If ordinary key/value Storage , Record 365 Bar record , If the number of users is large , The space needed will be huge , therefore Redis Provides Bitmap Bitmap this data structure ,Bitmap It is recorded by operating binary bits , That is to say 0 and 1; If you want to record 365 Day's clock in , Use Bitmap The form of expression is roughly as follows ：0101000111000111..........................., What good is that ？ Saving memory, of course 了 ,365 The sky is equal to 365 bit, also 1 byte = 8 bit , So it's equivalent to using 46 Only bytes .

BitMap Through a bit Bit to indicate the value or state of an element , Among them key It's the corresponding element itself , actually The bottom layer is also realized through the operation of string .Redis from 2.2 After the new version setbit, getbit, bitcount Wait a few

bitmap Relevant command .

setbit Set operation

setbit key offset value : Set up key Of the offset position value（1 or 0）

# Use bitmap To record the clock out record of the week in the above example, as shown below ：

# Monday ：1 Tuesday ：0 Wednesday ：0 Thursday ：1 Friday ：1 Saturday 0 Sunday 0（1 To punch in   0 Why don't you punch in ）

127.0.0.1:6379> setbit sign 0 1
(integer) 0
127.0.0.1:6379> setbit sign 1 0
(integer) 0
127.0.0.1:6379> setbit sign 2 0
(integer) 0
127.0.0.1:6379> setbit sign 3 1
(integer) 0
127.0.0.1:6379> setbit sign 4 1
(integer) 0
127.0.0.1:6379> setbit sign 5 0
(integer) 0
127.0.0.1:6379> setbit sign 6 0
(integer) 0
 

getbit The retrieval

getbit key offset obtain offset Set the value of the , Multiple default return is not set 0

127.0.0.1:6379> getbit sign 3                # See if you clock in on Thursday
(integer) 1
127.0.0.1:6379> getbit sign 6                # Check whether you clock in on Sunday
(integer) 0

bitcount Statistical operation

bitcount key [start, end] Statistics key The upper level is 1 The number of

# Count the clock in records this week , You can see that only 3 Days are clocking in

127.0.0.1:6379> bitcount sign
(integer) 3