Skip to main content

Mysql Interview Questions


  • Current mysql version : 8 ( last was 5.7 ,  5.7 to directly 8 )
  • SHOW FULL PROCESSLIST is used to see all the query executing when refresh the site.
  • 1 second == 1000 mili second, 0-500 ms responce time of any query is ok
How to Read the MySQL Slow Query Log : The MySQL slow query log is where the MySQL database server registers all queries that exceed a given threshold of execution time. This can often be a good starting place to see which queries are slowest and how often they are slow.
MySQL on your server is configured to log all queries taking longer than 0.1 seconds.

/var/log/mysql/mysql-slow.log
Use EXPLAIN or EXPLAIN EXTENDED to explain the query how it is executed.
MySQL describe or ANALYZE command shows the structure of the table.

Best practice in respect of performance :
1 - always use index,
2 - index types , primary index and combined field index like fname & lname in one index not two index,
3 - one index scan is faster than two,
4 - data type matters like in a query we use .... where numeric_value = "66", in this case the CPU takes too much time to execute, because first it will check as a string then check as a number,
so use proper data types.
5 - try to avoid the not indication in query  like IS NOT, IS NOT NULL,NOT IN ,NOT LIKE
6 - use inner join instead of left join
7 - UNION ALL is better than UNION
8 - use latest version of db 

Comments

Post a Comment

Popular posts from this blog

How to span column of custom table in Drupal

If you want to span the column of custom drupal table like below image, Follow the below code to make the header of the table , <?php $header = array('S.N','District', array('data' => '<div class ="house">Household </div><br><span>Rural</span> <p>Urban</p>','colspan' => 2), array('data' => '<div class ="house">Members</div> <br><span>Rural</span> <p>Urban</p>','colspan' => 2), 'Duplicate/Failed Registration', array('data' => '<div class ="house">Pending De duplication </div><br><span>Rural</span> <p>Urban</p>','colspan' => 2), 'Non Un-organised Workers', 'SSID Generated', 'No. of Card Personlised', ); $rows[] = arra...
1 comment
Read more

Drupal 8 : Link actions,Link menus,Link Tasks,Routings

Drupal 8 : Link actions,Link menus,Link Tasks,Routings Link actions Local actions have also been moved out of the hook_menu() system in Drupal 8 .Use actions to define local operations such as adding new items to an administrative list (menus, contact categories, etc). Local actions are defined in a YAML format, named after the module they are defined by. Such as menu_ui.links.action.yml for this example from menu_ui module: menu_ui.link_add:   route_name: menu_ui.link_add   title: 'Add link'   appears_on:     - menu_ui.menu_edit Here, menu_ui.link_add: It is the Unique name of the link action Most likely start with module name, route_name : Name of the route it means when click the link it redirect to this route, appears_on :  An array of route names for this action to be display on. Now how to know the Route name of any internal/external admin pages like below, By through the drupal console we achieve it, drupal debug:router...
Post a Comment
Read more

Cache In Drupal

Drupal 8 core caching modules: The Internal Page Cache module: this caches pages for anonymous users in the database. Pages requested by anonymous users are stored the first time they are requested and then are reused for future visitors. The Internal Dynamic Page Cache module: This is a key feature that Drupal 7 did not have. Unlike the Internal Page module, the Dynamic Page module aims to speed up the site for both anonymous and logged-in users. How Cache Works in Drupal: There are two modules available in the drupal core 1 - Internal page cache: The Internal Page Cache module caches pages for anonymous users in the database. Pages requested by anonymous users are stored the first time they are requested and then are reused. Configuring the internal page cache :   From the performance page we can set the maximum time how long browsers and proxies may cache pages based on the Cache-Control header. 2 - Internal dynamic page cache: Drupal 8 provides the Dynamic Page Cache m...
Post a Comment
Read more