The combination of max_allowed_packet variable and replication in MySQL is a common source of headaches. In a nutshell, max_allowed_packet is the maximum size of a MySQL network protocol packet that the server can create or read. It has a default value of 1MB (<= 5.6.5) or 4MB (>= 5.6.6) and a maximum size of 1GB. This adds some constraints in our replication environment:

• The master server shouldn’t write events to the binary log larger than max_allowed_packet

• All the slaves in the replication chain should have the same max_allowed_packet as the master server

Sometimes, even following those two basic rules we can have problems.

For example, there are situations (also called bugs) where the master writes more data than the max_allowed_packet …

Achieving the best possible MySQL Performance doesn’t have to be complicated. It’s all about knowing which tools are designed for the task at hand – along with some basic (yet often overlooked) best practices.

Join me Wednesday, May 14 at 10 a.m. Pacific for a free webinar titled, “Practical MySQL performance optimization.” I’ll be sharing the main areas for improving MySQL performance – along with what to specifically focus on in each. These will include:

• Hardware
• MySQL Configuration
• Schema and Queries
• Application Architecture

And as I mentioned earlier, I’ll also show you the best tools for the job and how …

One of the MySQL 5.6 features many people are interested in is Global Transactions IDs (GTIDs). This is for a good reason: Reconnecting a slave to a new master has always been a challenge while it is so trivial when GTIDs are enabled. However, using GTIDs is not only about replacing good old binlog file/position with unique identifiers, it is also using a new replication protocol. And if you are not aware of it, it can bite.

Replication protocols: old vs new

The old protocol is pretty straightforward: the slave connects to a given binary log file at a specific offset, and the master sends all the transactions from there.

The new protocol is slightly different: the slave first sends the range of GTIDs it has executed, and then the master sends every missing transaction. It also guarantees that a transaction with a given …

The new Percona Server 5.5.37-35.0 and Percona Server 5.6.17-65.0-56, announced yesterday (May 6), both include the open source version of the MySQL Audit Plugin. The MySQL Audit Plugin is used to log all queries or connections (“audit” MySQL usage). Until yesterday’s release, the MySQL Audit Plugin was only available in MySQL Enterprise.

EDIT:  Just to be clear, this implementation is alternative to the MySQL …

Tools for MySQL are a vital part of any deployment, so it’s important to use ones that are reliable and well-designed. Percona Toolkit is a collection of more than 30 command-line tools for MySQL, Percona Server, and MariaDB that can help database administrators automate a variety of database and system tasks. With so many available tools, however, it can be difficult knowing where to start.

For this reason I invite you to join me on Wednesday, May 7 at 10 a.m. Pacific time for a free webinar titled, “The top 9 Percona Toolkit tools that can make your job easier.” You can register directly …

Here on the Percona MySQL Support team, we often see issues where a customer is complaining about replication delays – and many times the problem ends up being tied to MySQL replication slave lag. This of course is nothing new for MySQL users and we’ve had a few posts here on the MySQL Performance Blog on this topic over the years (two particularly popular post in the past were: “Reasons for MySQL Replication Lag” and “Managing Slave Lag with MySQL Replication,” both by Percona CEO Peter Zaitsev).

In …

While Shard-Query can work over multiple nodes, this blog post focuses on using Shard-Query with a single node.  Shard-Query can add parallelism to queries which use partitioned tables.  Very large tables can often be partitioned fairly easily. Shard-Query can leverage partitioning to add paralellism, because each partition can be queried independently. Because MySQL 5.6 supports the partition hint, Shard-Query can add parallelism to any partitioning method (even subpartioning) on 5.6 but it is limited to RANGE/LIST partitioning methods on early versions.

The output from Shard-Query is from the commandline client, but you can use MySQL proxy to communicate with Shard-Query too.

In the examples I am going to use the schema from the Star Schema Benchmark.  I generated data for scale factor 10, which means about 6GB of data in the largest table. I am going to show a few different queries, and …

ScaleArc recently hired Percona to perform various tests on its database traffic management product. This post is the outcome of the benchmarks carried out by me and ScaleArc co-founder and chief architect, Uday Sawant.

The goal of this benchmark was to identify ScaleArc’s overhead using a real-world application – the world’s most popular (according to wikipedia) content management system and blog engine: WordPress.

The tests also sought to identify the benefit of caching for this type of workload. The caching parameters represent more real-life circumstances than we applied in the sysbench performance tests – the goal here was not just to saturate the cache. For this reason, we created an artificial WordPress blog with generated data. …

I have recently been involved in diagnosing the reasons behind OOM invocation that would kill the MySQL server process. Of course these servers were primarily running MySQL. As such the MySQL server process was the one with the largest amount of memory allocated.

But the strange thing was that in all the cases, there was no swapping activity seen and there were enough pages in the page cache. Ironically all of these servers were CentOS 6.4 running kernel version 2.6.32-358. Another commonality was the fact that vm.swappiness was set to 0. This is a pretty much standard practice and one that is applied on nearly every server that runs MySQL.

Looking into this further I realized that there was a change introduced in kernel 3.5-rc1 that altered the swapping behavior when “vm.swappiness=0″.

Below is the description of the commit that changed “vm.swappiness=0″ behavior, together with the diff:

$ git show …

While built-in replication has been a major cause for MySQL’s wide adoption, official tools to help DBAs manage replication topologies have typically been missing from the picture. The community has produced many good products to fill in this gap, but recently, Oracle has been filling it too with the addition of MySQL Utilities to the mix.

One part of the Utilities that has been generating interest recently is MySQL Fabric, and we will be discussing this project in an upcoming series of blog …