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Articles taggués ‘mysql performance tuning’

ERROR 1040…again

08/12/2019 Comments off

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…

Optimiser les performances de MySQL

06/12/2019 Comments off

Source: Optimiser les performances de MySQL (Quentin Busuttil)

Les bases de données SQL et plus particulièrement MySQL restent une des pierres angulaires de l’immense majorité des sites internet. MySQL fonctionne très bien out of the box, cependant, dès que la base se trouve assez sollicitée, on s’aperçoit que les réglages par défaut méritent une petite optimisation. Jetons un œil à tout ça !

Récemment, un des serveurs de Peerus commençait à avoir de sacrés pics de load lors des heures de forte charge, avec MySQL pour principal responsable. Une grosse centaine de connexions simultanées et quelques dizaines de requêtes par seconde sur des bases de plusieurs dizaines de giga. C’est un peu plus que le WordPress moyen, mais rien d’ingérable pour un MySQL bien réglé.

Dès lors, avant d’imaginer prendre un serveur plus puissant, sharder les tables ou je ne sais quoi encore, il faut tirer le maximum de notre cher SGBDR. Lire la suite…

Using MySQLTuner to Optimize MySQL

26/02/2019 Comments off

Tweaking MySQL is something you need to do regularly. Unlike PHP & Nginx tweaking, this is not a set & forget job!

We will use mysqltuner for tweaking mysql on a regular basis.

Tweaking MySQL default config first

Open /etc/mysql/my.cnf file & scroll down to [mysqld] section.

You will see many settings & some config variables. Some values are global while some are per-thread values. Its important because if you change something likejoin_buffer_size from 2M to 4M, it can shoot-up mysql’s max memory utilization by 300M memory (as per default 150 mysql’s max_connections value)

To start with, adjust following values:

max_connections = 50     #default is 150
wait_timeout = 30        #default is 28800

You can leave remaining as it is. Mysqltuner will guide you further.

Don’t forget to restart mysql. Command: service mysql restart

Using mysqltuner

If you are following our setup, you may already have mysqltuner installed. Otherwise run apt-get install mysqltuner on Ubuntu. Non-ubuntu guys can get it from here. It’s just a perl script!

When you run mysqltuner, it will show you a report with many suggestions. Just follow them. Exact suggestion will vary so its hard to cover all of them here. Rather I will give you some notes some of them are offered by mysqltuner itself.

Notes:

  1. Run mysqltuner after 24 hours. It you don’t, it will remind you by showing “MySQL started within last 24 hours – recommendations may be inaccurate.” Reason: mysqltuner recommendation may prove inaccurate.
  2. If it asks you to change value oftmp_table_size ormax_heap_table_size variable, make sure you change both and keep them equal. These are global values so feel free to increase them by large chunks (provided you have enough memory on server)
  3. If it asks you to tweak join_buffer_size, tweak in small chunks as it will be multiplied by value ofmax_connections.
  4. If it asks you to increase innodb_buffer_pool_size, make it large. Ideally, it should be large enough to accomodate your all innodb databases. If you do not have enough RAM consider buying some. Otherwise try to delete unwanted database. Do not ignore this as it can degrade performance significantly.

Apart from above, always keep an eye on following lines in Performance Metrics section of mysqltuner report:

[--] Total buffers: 2.6G global + 130.6M per thread (100 max threads)
[OK] Maximum possible memory usage: 15.3G (48% of installed RAM)
[OK] Highest usage of available connections: 81% (81/100)

Try to keep maximum possible memory less than 50%. Other lines can tell you, if your site is using too “less” mysql connections. In that case, you can reducemax_connections and increase other buffers more generously.

Also, whenever you make changes to mysql config and restart mysql server, always run mysqltuner immediately to check if by mistake you haven’t made maximum possible memory usage too high! Ignore any other suggestion it will give for next 24-hours!

mysqltuner & automatic password

As we use mysqltuner many times, it will be convenient use something like this.

Source: rtcamp.com

How To Optimize WordPress Performance With MySQL Replication On Ubuntu 14.04

11/02/2019 Comments off

Introduction

In this tutorial, we will teach you how to scale up your WordPress MySQL database server setup using master-slave database replication and the HyperDB plugin for WordPress. Adding more database servers to your environment in this manner allows your WordPress application to read from multiple database servers, increasing read performance.

MySQL replication reaps the most performance benefits for a system that processes frequent reads and infrequent writes, like most WordPress installations. By using a single-master with multiple-slave setup, you can add more slaves to scale your system, until you run out of network bandwidth or your master cannot handle the update load. If you wish, you can add more than one slaves by repeating the « slave » portions of the replication sections of this tutorial.

We are assuming that your setup includes two load balanced WordPress application servers that connect to a separate MySQL database server (see the prerequisites for a tutorial on how to set that up). It is not strictly necessary to have load balanced application servers to follow this tutorial, but your MySQL database server should be separate from your application servers.

Prerequisites

Before continuing with this tutorial, you should have completed two tutorials or have a similar environment:

After following those tutorials, to set up WordPress with two load balanced web application servers and a separate database server, you should have four VPSs. Because we will be dealing with several VPSs, for reference purposes, we will call your four existing VPSs the following:

  • haproxy-www: Your HAProxy server for layer 4 load balancing your WordPress web application servers. This is the entry point into your website
  • wordpress-1: Your first WordPress web application server
  • wordpress-2: Your second WordPress web application server
  • mysql-1: Your MySQL server for WordPress

That is, your environment should look something like this:

WordPress and Separate MySQL Database Server

In addition to your current environment, we will require one additional VPS during this tutorial. We will call it:

  • mysql-2: Your slave MySQL database server

Lire la suite…

10 essential performance tips for MySQL

05/11/2017 Comments off

As with all relational databases, MySQL can prove to be a complicated beast, one that can crawl to a halt at a moment’s notice, leaving your applications in the lurch and your business on the line.

The truth is, common mistakes underlie most MySQL performance problems. To ensure your MySQL server hums along at top speed, providing stable and consistent performance, it is important to eliminate these mistakes, which are often obscured by some subtlety in your workload or a configuration trap.

Luckily, many MySQL performance issues turn out to have similar solutions, making troubleshooting and tuning MySQL a manageable task.

Here are 10 tips for getting great performance out of MySQL.

MySQL performance tip No. 1: Profile your workload

The best way to understand how your server spends its time is to profile the server’s workload. By profiling your workload, you can expose the most expensive queries for further tuning. Here, time is the most important metric because when you issue a query against the server, you care very little about anything except how quickly it completes.

The best way to profile your workload is with a tool such as MySQL Enterprise Monitor’s query analyzer or the pt-query-digest from the Percona Toolkit. These tools capture queries the server executes and return a table of tasks sorted by decreasing order of response time, instantly bubbling up the most expensive and time-consuming tasks to the top so that you can see where to focus your efforts.

Workload-profiling tools group similar queries together, allowing you to see the queries that are slow, as well as the queries that are fast but executed many times.

Lire la suite…