September 30, 2014

Prevent MySQL downtime: Set max_user_connections

One of the common causes of downtime with MySQL is running out of connections. Have you ever seen this error? “ERROR 1040 (00000): Too many connections.” If you’re working with MySQL long enough you surely have. This is quite a nasty error as it might cause complete downtime… transient errors with successful transactions mixed with […]

2 cases for MySQL server overload

Your MySQL server is overloaded. You see hundreds of running queries in the SHOW PROCESSLIST taking many seconds to run, or can’t connect at all because all connections slots are busy. If you have worked with MySQL long enough you surely have seen it, probably more than once. This is what I would call “MySQL […]

Why MySQL Performance at Low Concurrency is Important

A few weeks ago I wrote about “MySQL Performance at High Concurrency” and why it is important, which was followed up by Vadim’s post on ThreadPool in Percona Server providing some great illustration on the topic. This time I want to target an opposite question: why MySQL performance at low concurrency is important for you. […]

How Percona diagnoses MySQL server stalls

We receive many requests for help with server stalls. They come under various names: lockup, freeze, sudden slowdown. When something happens only once or twice a day, it can be difficult to catch it in action. Unfortunately, this often leads to trial-and-error approaches, which can drag on for days (or even months), and cause a […]

10+ Ways to Crash or Overload MySQL

People are sometimes contacting me and asking about bugs like this which provide a trivial way to crash MySQL to the user with basic privileges and asking me what to do. My answer to them is – there is nothing new to it and they just sit should back and relax Really – there are […]

Why do you need many apache children ?

I already wrote kind of about same topic a while ago and now interesting real life case makes me to write again Most Web applications we’re working with have single tier web architecture, meaning there is just single set of apache servers server requests and nothing else – no dedicated server for static content, no […]

Are PHP persistent connections evil ?

As you probably know PHP “mysql” extension supported persistent connections but they were disabled in new “mysqli” extension, which is probably one of the reasons some people delay migration to this extension. The reason behind using persistent connections is of course reducing number of connects which are rather expensive, even though they are much faster […]

Wishes for new “Pure PHP” MySQL driver

If you’re following MySQL or PHP landscape you should have seen announcement by MySQL to develop pure PHP driver. If not – Here is FAQ . I’m to meet the team (Georg, Andrey etc) which will be developing this driver during my visit to Open Source Database Conference in November so I thought it would […]

Database problems in MySQL/PHP Applications

Article about database design problems is being discussed by Kristian. Both article itself and responce cause mixed feellings so I decided it is worth commenting: 1. Using mysql_* functions directly This is probably bad but I do not like solutions proposed by original article ether. PEAR is slow as well as other complex conectors. I […]

The Math of Automated Failover

There are number of people recently blogging about MySQL automated failover, based on production incident which GitHub disclosed. Here is my take on it. When we look at systems providing high availability we can identify 2 cases of system breaking down. First is when the system itself has a bug or limitations which does not […]