Record a query tuning process

premise

During the tuning process, use explaincommands to view the execution process, including execution time, scanning mode, whether indexes are used, etc., EXPLAIN usage analysis

开启查询sql执行时间：
\timing on
关闭查询sql执行时间：
\timing off

1. Problem description

A query interface is called frequently, and the query process is slow

2. Optimization ideas

1. First consider optimizing SQL statements
2. Secondly consider optimizing business code
3. Finally, consider whether you need to add a caching mechanism

3. Optimization process

3.1 Optimize SQL

Original SQL, group query data with the largest seq_id in each group, use in + group by to achieve

select name, version from yc_test where seq_id in(
    select max(seq_id) from yc_test group by name
);

3.1.1 SQL optimization ideas

• Consider adding indexes to speed up the query
• inWill be converted orand converted union all, the efficiency is lower. Consider using existsor joinreplacing. why?

3.1.2 Optimized SQL

select a.name, a.version from yc_test a inner join (
select max(seq_id) as seq_id from yc_test group by name
) b on a.seq_id=b.seq_id;

3.1.3 Comparison before and after SQL optimization

explain:

sql	advantage	Disadvantage
in implementation	sql simple	in will be converted to or and then to union all, which is less efficient, as shown in the figure for an extra layer of loop
inner join implementation	Reduce one layer of circulation and improve efficiency	In contrast, SQL is more complicated

3.2 Optimize business code

Combining functional business scenarios (which can be understood as historical records), read the code, and found that not all data needs to be persisted.
Optimization solution:

• 定时器Regularly clean up expired data to reduce data redundancy
• 业务逻辑Do control, judge whether there is extra data when saving data, and delete the extra data if there is.

3.3 Add caching mechanism

热点数据, You can consider caching in memory (variable cache), or storage in the database (Redis/Memcached).
Since the amount of data has been controlled and combined with later planning, no caching mechanism has been added.