Illustration of mongodb cluster deployment principle (3)

MongoDB There are three types of roles in the cluster deployment scenario of ： The actual data storage node 、 Configuration file storage node and routing access node .

The connected client is directly connected to the routing node , Query data from the configuration node , Query and store data on the actual storage node according to the query results .MongoDB There are single machine deployment 、 Copy Collection （ The main equipment ） Deploy 、 Split deployment 、 Hybrid deployment of replica set and fragmentation .

The mixed deployment is shown in the figure ：

file

In the mixed deployment mode, it is necessary to MongoDB The process of writing data is shown in the figure ：

file

Read in mixed deployment mode MongoDB The data flow in is shown in the figure below ：

file

For replica sets , There are two roles, master and slave , Writing data is different from reading data , The process of writing data is to write only to the master node , From master node to slave node asynchronously ：

file

While reading data only needs to read from any node , Specific to which node to read can be specified ：

file

about MongoDB The fragmentation of , Let's say we use an index key （ID） For the chip key ,ID The range of 0,50, Divide into 5 individual chunk, Store separately to 3 In a slice server , As shown in the figure ：

file

If there's a lot of data , When you need to add a slice server, you can just move chunk To divide the data evenly .

Configuration node ：

The server that stores configuration files actually stores chip keys and chunk as well as chunk And server The mapping relation of , The data model of configuration node storage represented by the above data is shown in the following table ：

Map1

Key range	chunk
[0,10)	chunk1
[10,20)	chunk2
[20,30)	chunk3
[30,40)	chunk4
[40,50)	chunk5

Map2

chunk	shard
chunk1	shard1
chunk2	shard1
chunk3	shard2
chunk4	shard2
chunk5	shard3

Routing nodes ：

Nodes with routing role play the role of load balancing in the case of fragmentation .

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