How to tune SQL

For example with MySQL

  • How to locate and optimize the SQL query slow
  • Causes leftmost matching principle of joint index
  • The index is established the better it

First, how to locate and optimize SQL query slow

Specific scenarios detailed analysis, presented here only a general idea

  1. According slow slow query log positioning SQL
  2. Explain the use of tools such as analysis sql
  3. Modify SQL or SQL as far as possible take the index

According slow slow query log positioning SQL

Use the command show variables like '% quer%'; to query related system variables;

  • show_query_log: log slow state, off is off, on open; using set global show_query_log = on; open
  • show_query_log_file: Slow logging file
  • long_query_time: each execution of SQL is that time has slow SQL, as a seconds; use set global long_query_time = 1; Set length

These commands only temporarily change these environment variables, if you want long-term use, you need to modify the configuration file my.ini

 

Use show status like '% show_queries%'; see the number of slow queries of this session, the session will be open once again cleared.

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Origin www.cnblogs.com/dasha/p/10926746.html