Understanding how MySQL handles connections and Troubleshooting MySQL error 1040 – Too many connections! How to interpret “MySQL error 1040 – Too many connections ! ” ?

When a client tries to log into MySQL it may sometimes be rejected and receive an error message saying that there are “too many connections“. This means that the maximum number of clients that may be connected to the server has been reached. Either the client will have to wait for another client to log off, or the administrator will have to increase the maximum number of connections allowed.

Information about connections to a server can be found using the SHOW STATUS statement:

SHOW STATUS LIKE 'max_used_connections';

Prerequisite – Few points to remember before working or troubleshooting MySQL ” Too many connections ! ” error

1. MySQL does not have it’s own thread handling mechanism / …

Modern internet infrastructure are complex.  Components and services are prone to failure.  Resiliency involves building redundancy, best practices and processes into your architecture to make you able to bend and not break.

• Migrating to cloud service providers
• Rearchitecting and refactoring applications to scale
• Scaling the database tier - MySQL and Oracle
• Building redundancy into every layer
• Deploying object caches - memcache
• Deploying page caches - varnish
• Migrating to Innodb - transactional storage engine
• Infrastructure design
• Infrastructure automation
• Disaster Recovery
• Business Continuity with cloud deployments

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There are a lot of scalability challenges we see with clients over and over. The list could easily include 20, 50 or even 100 items, but we shortened it down to the biggest five issues we see.

1. Tune those queries

By far the biggest bang for your buck is query optimization. Queries can be functionally correct and meet business requirements without being stress tested for high traffic and high load. This is why we often see clients with growing pains, and scalability challenges as their site becomes more popular. This also makes sense. It wouldn't necessarily be a good use of time to tune a query for some page off in a remote corner of your site, that didn't receive real-world traffic. So some amount of reactive tuning is common and appropriate.

Enable the slow query log and watch it. Use …