⚠️ User already has more than ‘max_user_connections’ active connections [✅ SOLVED]

Noticed a lot of Crawler errors on the Google Adsense console:

So I enabled the WP_DEBUG and run a stress test with vegeta on the website:

echo "GET https://domain.com/" | vegeta attack -duration=30s -rate=250 | tee results.bin | vegeta report

the website became unavailable and the following error was shown: User already has more than ‘max_user_connections’ active connections

This explains the errors in Google SC because the crawler most likely also encountered this error.

To resolve this issue, it is important to check which queries are problematic. For this, you can check the following guide: How to properly DEBUG in WordPress

Check active connections

On cPanel you can see the active connections from WHM > Show MySQL® Processes

or if you don’t have access to the WHM *(e.g. you are on shared hosting) then from the terminal run:

mysqladmin -u USERNAME_HERE -p processlist

This will display all active MySQL connections for that user.

The next step is to determine what is causing the problem, in WordPress the most common culprit is:

• A: Plugin that was recently installed or updated
• B: Corrupt tables in the Database

In this post I will go over 3 examples of problems that are causing the “User already has more than ‘max_user_connections’ active connections” error on a WordPress website:

• Plugin is storing data inside WP core tables (wp_options)
• The plugin is using custom tables but the queries and tables are not optimized
• Multiple WP websites use the same MySQL user

Understanding the query

• How to display database queries
• Save database queries for analysis

1. example – Plugin is storing data inside WP core tables (wp_options)

Another example of a plugin that is causing this problem is All In One WP Security which uses the wp_options table to store data and leaves it after being uninstalled:

In this case, the plugin leftover 900k of rows in the wp_options table, and queries to that table had to go through all records which became a problem.

To delete residual data after uninstalling a plugin read this guide: How to safely remove database tables after plugin deactivation

2. example – Plugin queries & tables are not optimized

First take a look into the query that causes the problem, in my case the query ALTER_TABLE wpoe_snax_collections … is the last query that is active, and all new queries are waiting for this one to finish.

Since this plugin is a must for the website and has to be used, let’s look into ways to optimize the database and MySQL service.

This query is used by a plugin named Snax – Viral Content Builder and I can confirm that it is the culprit by renaming the plugin folder and by doing so temporarily disabling it.

To learn exactly what this query does and why it needs a lot of time to finish, we can use the EXPLAIN:

EXPLAIN ALTER_TABLE wpoe_snax_collections ...

This will show you how the query is executed: if there are indexes, autoload is enabled, does the whole table need to be scanned, etc.

3. example – MySQL user is used on multiple databases

In this example, the MySQL user is used for multiple WordPress websites and often causes the “User already has more than ‘max_user_connections’ active connections” error.

Using the same MySQL user for many databases is seen as a poor security practice. For instance, if the server has a 20 connection limit per user, the limit would frequently be hit, resulting in an error message being displayed on all websites using that user.

Fixing slow queries

Developers of plugins and themes can speed up slow queries inside their code, however for end users, there are several things you can do to speed up queries on your website:

Adding Indexes

When running a query on a standard table, the entire table needs to be scanned, which might be problematic for large tables. Indexes arrange the information in tables in a way that speeds up each query.

To add index to wp_postmeta table run:

CREATE INDEX wp_postmeta_wpxss ON wp_postmeta (meta_key)

Adding High-performance keys

On existing tables, We can add high-performance keys that match the most common WordPress queries, for wp_postmeta:

ALTER TABLE wp_postmeta ADD UNIQUE KEY meta_id (meta_id);
ALTER TABLE wp_postmeta DROP PRIMARY KEY;
ALTER TABLE wp_postmeta ADD PRIMARY KEY (post_id, meta_key, meta_id);
ALTER TABLE wp_postmeta DROP KEY post_id;
ALTER TABLE wp_postmeta DROP KEY meta_key;
ALTER TABLE wp_postmeta ADD KEY meta_key (meta_key, post_id);

This will create new high-performance keys:

For more examples and code snippets for other WordPress tables check this post: Adding high-performance keys to MySQL tables to speed up WordPress

Using Transients

WordPress transients allow us to save the results of the query so that they can be displayed more quickly the next time.

But because transients are stored inside the wp_options table, you should only use them for global and necessary data.

Here is an example:

if ( false === ( $results = get_transient( 'transient_key_name' ) ) ) {
  $results = ...;

  set_transient( 'transient_key_name', $results, 60 * 60 ); 
}

For more useful examples check WP.org Common APIs Handbook and WPengine.com Guide to Transients in WordPress