April 18, 2014

Impact of memory allocators on MySQL performance

MySQL server intensively uses dynamic memory allocation so a good choice of memory allocator is quite important for the proper utilization of CPU/RAM resources. Efficient memory allocator should help to improve scalability, increase throughput and keep memory footprint under the control. In this post I’m going to check impact of several memory allocators on the […]

Helgrinding MySQL with InnoDB for Synchronisation Errors, Fun and Profit

It is no secret that bugs related to multithreading–deadlocks, data races, starvations etc–have a big impact on application’s stability and are at the same time hard to find due to their nondeterministic nature.  Any tool that makes finding such bugs easier, preferably before anybody is aware of their existence, is very welcome.

Getting MySQL Core file on Linux

Core file can be quite helpful to troubleshoot MySQL Crashes yet it is not always easy to get, especially with recent Linux distributions which have security features to prevent core files to be dumped by setuid processes (and MySQL Server is most commonly ran changing user from “root” to “mysql”). Before you embark on enabling […]

How to debug long-running transactions in MySQL

Among the many things that can cause a “server stall” is a long-running transaction. If a transaction remains open for a very long time without committing, and has modified data, then other transactions could block and fail with a lock wait timeout. The problem is, it can be very difficult to find the offending code […]

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 […]

Logging MySQL queries from the client instead of the server

The “slow query log” is the single most valuable way to examine query execution on your MySQL server. Queries are logged with timing information, and in the case of Percona Server, a great deal of additional performance and other diagnostic information. But the execution time recorded in the log is the time the query took […]

Ultimate MySQL variable and status reference list

I am constantly referring to the amazing MySQL manual, especially the option and variable reference table. But just as frequently, I want to look up blog posts on variables, or look for content in the Percona documentation or forums. So I present to you what is now my newest Firefox toolbar bookmark: an option and […]

The story of one MySQL Upgrade

I recently worked on upgrading MySQL from one of very early MySQL 5.0 versions to Percona Server 5.1. This was a classical upgrade scenario which can cause surprises. Master and few slaves need to be upgraded. It is a shared database used by tons of applications written by many people over more than 5 years […]

Faster MySQL failover with SELECT mirroring

One of my favorite MySQL configurations for high availability is master-master replication, which is just like normal master-slave replication except that you can fail over in both directions. Aside from MySQL Cluster, which is more special-purpose, this is probably the best general-purpose way to get fast failover and a bunch of other benefits (non-blocking ALTER […]

Apache PHP MySQL and Runaway Scripts

Sometimes due to programming error or due to very complex query you can get your PHP script running too long, well after user stopped waiting for the page to render and went browsing other sites. Looking at Server-Status I’ve seen scripts executing for hours sometimes which is obviously the problem – they take Apache Slot, […]