Redis introduction complete tutorial: List explanation

list （list） Type is used to store multiple ordered strings , Pictured 2-18 Shown ,a、
b、c、d、e Five elements form an ordered list from left to right , Each string in the list
It's called the element （element）, A list can store at most 2 32 -1 Elements . stay Redis in , can
To insert... At both ends of the list （push） And pop up （pop）, You can also get the element column of the specified range
surface 、 Get the elements of the specified index subscript, etc （ Pictured 2-18 Sum graph 2-19 Shown ）. A list is a comparison
More flexible data structure , It can act as a stack and a queue , There are many applications in practical development
scene .

List types have two characteristics ： First of all 、 The elements in the list are ordered , That means you can
Get a list of elements or elements in a range by index subscript , For example, to get a graph 2-19
Of the 5 Elements , It can be executed lindex user：1：message4（ Index from 0 Count up ） You can get
To the elements e. second 、 Elements in a list can be repetitive , For example, figure 2-20 The list shown contains
Two strings were a.

 

These two characteristics will be introduced after the introduction of set and ordered set , It's going to be more prominent , So I'm taking the exam
Before considering whether to use this data structure , First of all, we need to understand the characteristics of the list data structure .

2.4.1　 command
The following will follow the 5 There are three types of operation to introduce the command , The command is shown in the table 2-4 Shown .
 

1. Add operation
（1） Insert the element from the right
rpush key value [value ...]
The following code inserts elements from right to left c、b、a：
127.0.0. 1:6379> rpush listkey c b a
(integer) 3
lrange0-1 Command can get all the elements of the list from left to right ：
127.0.0.1:6379> lrange listkey 0 -1
1) "c"
2) "b"
3) "a"

（2） Insert the element from the left
lpush key value [value ...]
Usage and rpush identical , Just insert... From the left , No more details here .
（3） Inserts an element before or after an element
linsert key before|after pivot value
linsert The command will find in the list equal to pivot The elements of , In front of it （before） Or after
（after） Insert a new element value, For example, the following operation will be in the list of elements b Insert before
java：
127.0.0.1:6379> linsert listkey before b java
(integer) 4
The return result is 4, Represents the length of the current command , The current list changes to ：
127.0.0.1:6379> lrange listkey 0 -1
1) "c"
2) "java"
3) "b"
4) "a"
2. lookup
（1） Gets a list of elements in the specified range
lrange key start end
lrange Operation gets all the elements in the specified index range of the list . The index subscript has two characteristics  

spot ： First of all , Index subscripts from left to right are 0 To N-1, But from right to left is -1 To -N.
second ,lrange Medium end It contains the option itself , This and many programming languages do not contain end Not really
identical , For example, if you want to get the second 2 To the first 4 Elements , You can do the following ：
127.0.0.1:6379> lrange listkey 1 3
1) "java"
2) "b"
3) "a"
（2） Gets the element of the list with the specified index index
lindex key index
For example, the last element in the current list is a：
127.0.0.1:6379> lindex listkey -1
"a"
（3） Get list length
llen key
for example , The following example shows that the current list length is 4：
127.0.0.1:6379> llen listkey
(integer) 4
3. Delete
（1） The element pops up from the left side of the list
lpop key

The following operation will list the leftmost elements c Will be a pop-up , After the pop-up, the list changes to java、b、
a：
127.0.0.1:6379>t lpop listkey
"c"
127.0.0.1:6379> lrange listkey 0 -1
1) "java"
2) "b"
3) "a"
（2） Pops up from the right side of the list
rpop key
How to use it and lpop It's the same , Just pop up from the right side of the list , There's no more here
Statement .
（3） Deletes the specified element
lrem key count value
lrem The command will find in the list equal to value To delete the elements of , according to count Different
There are three situations ：
·count>0, From left to right , Delete the most count Elements .
·count<0, From right to left , Delete the most count Absolute value element .
·count=0, Delete all .
For example, insert from left to right into the list 5 individual a, So the current list becomes “a a a a a java b a”,
The following operation will start from the left side of the list to delete 4 A for a The elements of ：

127.0.0.1:6379> lrem listkey 4 a
(integer) 4
127.0.0.1:6379> lrange listkey 0 -1
1) "a"
2) "java"
3) "b"
4) "a"
（4） Trim the list by index range
ltrim key start end
for example , The following operation will only keep the list listkey The first 2 One to the first 4 Elements ：
127.0.0.1:6379> ltrim listkey 1 3
OK
127.0.0.1:6379> lrange listkey 0 -1
1) "java"
2) "b"
3) "a"
4. modify
Modifies the element of the specified index index ：
lset key index newValue
The following operation will list listkey No 3 The elements are set to python：
127.0.0.1:6379> lset listkey 2 python
OK
127.0.0.1:6379> lrange listkey 0 -1
1) "java"
2) "b"
3) "python"
5. Blocking operations
The blocking pop-up is as follows ：

blpop key [key ...] timeout
brpop key [key ...] timeout
blpop and brpop yes lpop and rpop Blocking version of , They're not in the same direction as the pop-up , Use
The method is basically the same , So here is brpop Command to explain ,brpop The command has two parameters ：
·key[key...]： Keys for multiple lists .
·timeout： Blocking time （ Company ： second ）.
1） The list is empty. ： If timeout=3, So the client has to wait until 3 Seconds later , If
timeout=0, So the client has been blocking and waiting ：
127.0.0.1:6379> brpop list:test 3
(nil)
(3.10s)
127.0.0.1:6379> brpop list:test 0
... Blocking ...
If data is added during this period element1, The client immediately returns ：
127.0.0.1:6379> brpop list:test 3
1) "list:test"
2) "element1"
(2.06s)
2） The list is not empty ： The client will immediately return .
127.0.0.1:6379> brpop list:test 0
1) "list:test"
2) "element1"
In the use of brpop when , There are two points to note .
The first point , If it's multiple keys , that brpop Will traverse the key from left to right , Once there is a key

Can pop up elements , The client immediately returns ：
127.0.0.1:6379> brpop list:1 list:2 list:3 0
.. Blocking ..
At this point, the other client will send list：2 and list：3 Insert elements ：
client-lpush> lpush list:2 element2
(integer) 1
client-lpush> lpush list:3 element3
(integer) 1
The client will immediately return list：2 Medium element2, because list：2 The first thing to pop up
Elements ：
127.0.0.1:6379> brpop list:1 list:2 list:3 0
1) "list:2"
2) "element2_1"
Second point , If multiple clients execute on the same key brpop, Then execute first brpop life
So that the client can get the pop-up value .
client 1：
client-1> brpop list:test 0
... Blocking ...
client 2：
client-2> brpop list:test 0
... Blocking ...
client 3：

client-3> brpop list:test 0
... Blocking ...
At this point, another client lpush An element to list：test In the list ：
client-lpush> lpush list:test element
(integer) 1
So the client 1 You'll get the most elements , Because the client 1 The first to perform brpop, And the client 2
And the client 3 Keep blocking ：
client> brpop list:test 0
1) "list:test"
2) "element"
I've finished with the basic list commands , surface 2-5 It's the time complexity of these commands ,
Developers can refer to this table to select the appropriate command .

 

 

2.4.2　 Internal encoding
There are two types of internal encoding for list types .
·ziplist（ Compressed list ）： When the number of elements in the list is less than list-max-ziplist-entries To configure
（ Default 512 individual ）, At the same time, the value of each element in the list is less than list-max-ziplist-value When the configuration
（ Default 64 byte ）,Redis Will choose ziplist As an internal implementation of the list to reduce memory
use .
·linkedlist（ Linked list ）： When the list type cannot satisfy ziplist The condition of ,Redis Will use
linkedlist As an internal implementation of the list .
The following example demonstrates the internal encoding of a list type , And the corresponding changes .
1） When the number of elements is small and there are no large elements , The internal code is ziplist：
127.0.0.1:6379> rpush listkey e1 e2 e3
(integer) 3
127.0.0.1:6379> object encoding listkey
"ziplist"
2.1） When the number of elements exceeds 512 individual , The internal code becomes linkedlist：
127.0.0.1:6379> rpush listkey e4 e5 ... Ignore ... e512 e513
(integer) 513
127.0.0.1:6379> object encoding listkey
"linkedlist"
2.2） Or when an element exceeds 64 byte , The internal code will also become linkedlist：
127.0.0.1:6379> rpush listkey "one string is bigger than 64 byte...............
................."
(integer) 4
127.0.0.1:6379> object encoding listkey

"linkedlist"