Distributed | several steps of rapid read / write separation

author ： Wang Juan

Love can be born dble Team test members , Mainly responsible for dble Requirements testing , Automated writing and community problem solving . People don't talk too much .

In this paper, the source ： Original contribution

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dble from 3.20.10 Version start ⽀ It has a simple read-write separation function , It can be separated from the functions of database and table ⽤.

How to quickly have read-write separation ？

First step , Get a group ready mysql real example , And ensure that this group mysql The master-slave replication relationship of the instance is normal . The following uses one master and two slaves mysql：

Lord ：172.100.9.6:3307

from ：172.100.9.2:3307、172.100.9.3:3307

Separate to 2 From instances show slave status , Check whether the replication relationship is normal .

The second step , stay db.xml To configure mysql example . as follows ：

<dbGroup rwSplitMode="1" name="ha_group1" delayThreshold="100">
    <heartbeat>show slave status</heartbeat>
    <dbInstance name="hostM1" password="******" url="172.100.9.6:3307" user="test" maxCon="1000" minCon="10" primary="true"/>
    <dbInstance name="hostS1" password="******" url="172.100.9.2:3307" user="test" maxCon="1000" minCon="10" readWeight="1"/>
    <dbInstance name="hostS2" password="******" url="172.100.9.3:3307" user="test" maxCon="1000" minCon="10" readWeight="1"/>
</dbGroup>

To configure dbGroup The following parameters should be paid attention to ：

rwSplitMode： Load balancing mode for read operations , Optional value 0/1/2/3
In into ⾏ When reading load balancing, it will proceed according to this configuration ⾏
0： Do not balance , Distribute directly to the primary instance , Slave instances will be ignored , Will not try to build ⽴ Connection pool , But there will be ⼼ Jump connect
1： Read operations are balanced across all slave instances , When all slave instances are not ⽤ when , An error will be reported when issuing a statement .
2： Read operations are balanced across all instances .
3： Read operations are balanced across all slave instances , When all slave instances are not ⽤ when , Send the statement to the main instance .

delayThreshold： Specify the master-slave delay threshold , Unit second , Default -1 , surface ⽰⽆ Delay
In into ⾏ When reading the load balance, it will be based on the latest ⼀ Time of ⼼ Skip status and delay of Reading database and main database ⾏ Judge , If master-slave replication does not ⼯ The delay in making or copying exceeds delayThreshold To configure , Then it is considered that this node is not suitable for ⾏ Read , Depend on ⼼ Jump statement is show slave status . If delayThreshold=-1 Then the load balancing selection will not be read ⾏ Delay detection .

readWeight： Node weight ( Load balancing makes ⽤)
During the load balancing process, you will check whether the weights of all nodes are equal , If it's not equal , Then the pressure will be allocated according to the weight ⼒. The value must be ⼤ Is equal to 0 The integer of . If it is equipped with 0 surface ⽰ This node does not participate in reading . Attention should be paid to , Total weight （ Sum of weights of all nodes ） must ⼤ On 0.

How to distinguish between read nodes and write nodes ？

Write nodes ：primary=“true”

Read node ：primary No configuration or primary=“false”

The third step ,user.xml Add read / write separation users . adopt dbGroup Assign to db.xml in dbGroup Of name.

<rwSplitUser name="rwSplit1" password="111111" dbGroup="ha_group1" />

Step four , To dble The management side executes reload @@config_all , Make configuration effective . At this point, you can use the newly created read-write separation user rwSplit1 Sign in dble 了 .

How to verify whether the read / write separation configuration is effective ？

Separate to 3 individual mysql Instance execution ：set global general_log = on , Turn on general log .

Use rwSplit1 The user login dble 8066 port , Perform the following sql ：

insert into test_table values (1, ‘name1’),(2, ‘name2’);

select * from test_table;

View the write node general log ,insert The statement is sent to the write node .

Point by point view 2 The number of read nodes general log ,select Statement to one of the read nodes .

Add ：

1、 At the same time open dble When reading and writing the functions of separation and database and table separation , Sub database and sub table quotation ⽤ Of dbGroup and Read write separation citation ⽤ Of dbGroup Must be independent of each other ⽴.rwSplitUser lead ⽤ Of dbGroup , Only in the db.xml It can be defined in .

2、 Multiple rwSplitUser Can lead to ⽤ Same as ⼀ individual dbGroup .

3、dble Read / write separates which statements are sent to the primary instance , Which statements are sent to the slave instance ？ Reference resources ：https://github.com/actiontech/dble/discussions/3145