Databases, Systems & Networks

A pretty common topic in Support tickets is the rather infamous error: ERROR 1040: Too many connections. The issue is pretty self-explanatory: your application/users are trying to create more connections than the server allows, or in other words, the current number of connections exceeds the value of the max_connections variable.

This situation on its own is already a problem for your end-users, but when on top of that you are not able to access the server to diagnose and correct the root cause, then you have a really big problem; most times you will need to terminate the instance and restart it to recover.

Root user can’t connect either! Why!?

In a properly set up environment, a user with SUPER privilege will be able to access the instance and diagnose the error 1040 problem that is causing connection starvation, as explained in the manual:

mysqld actually permits max_connections + 1 client connections. The extra connection is reserved for use by accounts that have the SUPER privilege. By granting the privilege to administrators and not to normal users (who should not need it), an administrator who also has the PROCESS privilege can connect to the server and use SHOW PROCESSLIST to diagnose problems even if the maximum number of unprivileged clients are connected.

But we see lots of people who give SUPER privileges to their application or script users, either due to application requirements (dan Lire la suite…

Source: digitalocean

Introduction

MySQL comes with a handy little diagnostic tool called mysqlslap that’s been around since version 5.1.4. It’s a benchmarking tool that can help DBAs and developers load test their database servers.

mysqlslap can emulate a large number of client connections hitting the database server at the same time. The load testing parameters are fully configurable and the results from different test runs can be used to fine-tune database design or hardware resources.

In this tutorial we will learn how to use mysqlslap to load test a MySQL database with some basic queries and see how benchmarking can help us fine-tune those queries. After some basic demonstrations, we will run through a fairly realistic test scenario where we create a copy of an existing database for testing, glean queries from a log, and run the test from a script.

The commands, packages, and files shown in this tutorial were tested on CentOS 7. The concepts remain the same for other distributions. Lire la suite…

One of the interesting new tools in MySQL 5.1.4 is mysqlslap, a load emulator that lets you see how well a particular query set or table engine performs under high-load conditions.

A query that consumes too many database resources may be the result of designing tables incorrectly, choosing the wrong table type, or creating an inefficient query. When a query eats up a lot of database resources, it can negatively affect other application components. By using mysqlslap to stress test a server in a non-public environment, you will discover these errors sooner, allowing you to you avoid a database meltdown once your application goes live.

This tutorial shows how you can use mysqlslap to run stress tests involving multiple clients, custom queries, different table engines, and much more. Lire la suite…