Wordpress一直在执行这个SQL查询？

Question

My Wordpress site doesn't have a lot of traffic but I keep seeing this SQL query via "SHOW PROCESS;" in MySQL:

SELECT SQL_CALC_FOUND_ROWS  wp_posts.ID
FROM wp_posts
WHERE 1=1 AND wp_posts.post_type = 'post' AND (wp_posts.post_status = 'publish')
ORDER BY wp_posts.post_date DESC LIMIT 0, 10

I have turned off all plugins and updated to the latest Wordpress version (4.1). And I also use the default theme built in with WordPress (2014).

Whenever I run "SHOW PROCESS;", I can see at least 3-8 of this query running, sometimes even more, like 10+ of this query while the traffic is quite light (even idle).

I am asking because MySQL is using a lot of CPU resource and I am wondering why this query keeps showing up multiple times every second I run "SHOW PROCESS" on.

Answer 1

What you are seeing are normal and expected and there is not much you can do about that. It is normal to have up to 30 SQL queries on a page load. More than that should be inspected.

So what are all these queries and where do they come from?

• On every page load, the main query is executed, even on a 404 page or when a bunch of garbage is enetered into the URL field/address bar. The URL is parsed and converted in query arguments which is used by WP_Query to retrieve the posts from the db according to the arguments coming from the URL. WP_Query converts all the arguments and requests into a single SQL query which it uses to communicate with the db to retrieve what is been asked of it. This is one db hit which you can't do anything about and most probabaly this is the SQL query from your question.

• Any custom query ( new WP_Query , get_posts and get_pages ) is converted to an SQL query to query and retrieve posts from the db

• Your navigation menu make use of functions that is converted to SQL queries to construct the main navigation menu

• Function used to display tags, term and categories attached to a post uses SQL queries to retrieve the tags/terms/categories from the DB

• Most of the default widgtes uses custom queries and/or functions that uses SQL queries to get info from the db

• Some of the conditional tags uses SQL queries to check a condition against an entry in the db

• On pages, the main query makes an additional SQL query to retrieve the page template used for the specific page

• Wordpress runs some processes which uses SQL queries in the background

• Related or popular post sections also uses custom queries which translates in SQL queries to retrieve the relevant posts

These are just some of the stuff that automatically hits the db on each page load, some can be controlled, others cannot, but in the end of the day, without these queries you won't have the visual experience or functionalities in your pages

I would suggest that you download and install Query Monitor in your test installation. Do not run this tool on production site as the info is printed to screen directly. This tool prints out all the queries/db hits on every page load and the time that these queries takes to execute. With this you will get a good idea of what is going on and which functions hits the db.

As I already stated, it is normal to have up to 30 SQL queries (db hits) on a single page load. More that this should be inspected and this can normally be rectified by optimizing your code

The most important factor to remember and to consider is the amount of queries vs the actual time taken to execute them. This should be your most important factor in deciding which route to go. I have shown many times in the past that four well constructed queries is sometimes 10 times faster than one query in which you want to do everything at once.

Also, make proper use of caches and transients on big bulky operations that cannot be streamlined. You will at some stage run into a query that makes 70 db hits no matter what you try.

EDIT

Just to add, the amount of traffic does not increase or decrease the amount of SQL queries that runs by default on a given page. The amount of SQL queries are solely determined by the processes being run to completely load the page