The SQL response is slow. What are your troubleshooting ideas?

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If the interview asks you , perform SQL Slow response , What are your troubleshooting ideas and solutions ？ This is a real interview question shared with me by a small partner who went to a certain place to try , Today, I would like to share my thoughts with you .

1、 Investigation thought

If you execute SQL Slow response , I think there may be the following 4 One reason ：

The first 1 One reason ： No index or Cause index to fail .

The first 2 One reason ： There are too many data in a single table , Cause query bottleneck

The first 3 One reason ： Network reasons or the machine load is too high .

The first 4 One reason ： Hot data causes single point load imbalance .

Next , I aim at the above situations , Let's talk about my solutions .

2、 Solution

The first 1 In this case ： The index is invalid or there is no index

First , Can open MySQL Slow query log , Collect the contents of slow query logs for a period of time , Then find out what took the longest SQL sentence , For these SQL Statement analysis .

For example, you can use the execution plan explain To view the SQL Whether there is a hit index . If you find slow queries SQL No hit index , You can try to optimize these SQL sentence , Guarantee SQL Execute by index . If SQL If there is no way to optimize the structure , Consider adding the corresponding index to the table . We are optimizing SQL Or when adding an index , Must conform to the leftmost matching principle .

The first 2 In this case ： There are too many data in a single table , Conditions that cause query bottlenecks . Even if SQL The statement is indexed , The performance is not particularly good . At this time, we need to consider table segmentation . Table segmentation rules are generally divided into two types , One is horizontal segmentation , One is vertical segmentation .

Horizontal segmentation means that a large table with tens of millions of data rows , Split into multiple small tables according to the business PK , These small watches may reach 100 Zhang even 1000 Zhang .

That vertical segmentation means , Combine multiple columns in a single table , According to the business logic, put the columns with high relevance into the same table .

In addition to this sub table , We can also divide the warehouse ,

For example, we have split up 1000 surface , then , Put the suffix 0-100 The tables of are placed in the same database instance , then ,100-200 Put the table of into another database instance , And so on 1000 Table storage 10 Database instances . In this case , We can route requests to different database instances according to the business primary key , Thus, the traffic borne by each database instance is relatively small , To achieve the purpose of improving database performance .

The first 3 In this case ： Network reasons or excessive machine load , We can separate reading and writing .

such as MySQL Support the distributed deployment of one master and multiple slaves , We can use the main library only to handle the operation of writing data , Multiple slave libraries are only used to handle read operations . In scenarios with large traffic , You can increase the load capacity of the database by adding slave libraries , So as to improve the overall performance of the database .

The first 4 In this case ： Hot data leads to unbalanced load at a single point .

In this case , In addition to adjusting the database itself , You can also increase the cache . Pre store the hot data with frequent queries into the cache , such as Redis、MongoDB、ES etc. , To relieve the pressure of data , So as to improve the response speed of the database .

The above is my view on the implementation SQL Slow response troubleshooting ideas and solution understanding , I hope I can help you . Pay attention to me , The interview is no longer difficult ！

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