We have been using SHOW ENGINE INNODB MUTEX command for years. It shows us mutex and rw-lock information that could be useful during service troubleshooting in case of performance problems. As Morgan Tocker announced in his blog post the command will be removed from MySQL 5.7 and we have to use performance_schema to get that info.

The documentation of MySQL also says that most of the command output has been removed from 5.6 and that we can find similar info in performance_schema. It doesn’t show any examples of how to use performance_schema or what is the query we need to use from now on. It is also important to mention that 5.6 doesn’t show any warning about the feature being deprecated.

This is a short blog post to show how to configure performance_schema and get the info we need. Hoping it will end …

Sometimes it is desired to use particular software versions in production, and not necessary the latest ones. There may be several reasons for that, where I think the most common is when a new version should spend some time in testing or a staging environment before getting to production. In theory each new version is supposed to be better as usually it contains a handful of bug fixes and even new or improved functionality. However there is also a risk of some regression or a new bug introduction as a side effect of code changes.

Quite often DBAs want the same MySQL version to be installed on all database instances, regardless of what actually is the latest version available in the software provider’s repository. There are several ways to achieve this:
* download specific version packages manually and then install them,
* have custom local repository mirror where you decide when and which version gets there, and just update …

Query caching is one of the prominent features in MySQL and a vital part of query optimization. It is important to know how it works as it has the potential to cause significant performance improvements – or a slowdown – of your workload.

The MySQL query cache is a global one shared among the sessions. It caches the select query along with the result set, which enables the identical selects to execute faster as the data fetches from the in memory. It is important to have everything identical, no new comments, spaces, or most significantly differences in the WHERE clause. Basically when you trigger a select query, if it is available in the cache; it fetches from there or it considers the query as a new one and will go to the parser.

Even though it has some nice advantages, the MySQL query cache has its own downsides too. Well, let’s think about this: If you are frequently updating the table, you are then invalidating …

State Snapshot Transfer (SST) is used in Percona XtraDB Cluster (PXC) when a new node joins the cluster or to resync a failed node if Incremental State Transfer (IST) is no longer available. SST is triggered automatically but there is no magic: If it is not configured properly, it will not work and new nodes will never be able to join the cluster. Let’s have a look at a few classic issues.

Port for SST is not open

The donor and the joiner communicate on port 4444, and if the port is closed on one side, SST will always fail.

You will see in the error log of the donor that SST is started:

[...]
141223 16:08:48 [Note] WSREP: Node 2 (node1) requested state transfer from '*any*'. Selected 0 (node3)(SYNCED) as donor.
141223 16:08:48 [Note] WSREP: Shifting SYNCED -> DONOR/DESYNCED (TO: 6)
141223 16:08:48 …

Some time ago, Peter Zaitsev posted a blog titled “How well does your table fits in innodb buffer pool?” He used some special INFORMATION_SCHEMA tables developed for Percona Server 5.1 to report how much of each InnoDB table and index resides in your buffer pool.

As Peter pointed out, you can use this view into the buffer pool to watch a buffer pool warm up with pages as you run queries. You can also use it for capacity planning. If you expect some tables need to be fully loaded in the buffer pool to be used efficiently, but the buffer pool isn’t large enough to hold them, then it’s time to increase the size of the buffer pool.

The problem, however, was that system tables change from version to version. Specifically, the INNODB_BUFFER_POOL_PAGES_INDEX table no longer exists in Percona Server 5.6, and the …

It has been a while since I have looked at InnoDB crash recovery. A lot has change in the last few years – we have serious crash recovery performance improvements in MySQL 5.5 and MySQL 5.6, we have solid state drives raising as typical high performance IO subsystem and we also have the ability to set much larger log files and often have a much larger InnoDB Buffer Pool to work with.

First let me revisit the challenge with have with InnoDB configuration. For write-intensive workloads it is extremely important to size innodb_log_file_size for good performance, however the longer log file size you have the longer you might have to wait for InnoDB to complete crash recovery, which impacts your recovery strategy.

How much can innodb_log_file_size impact performance? Massively! Doing intensive writes to a database that well fits in memory, I’d say there’s a 10x …

This is a long overdue blog post from London’s 44con Cyber Security conference back in September. A lot of old memories were brought to the front as it were; the one I’m going to cover in this blog post is: file carving.

So what is file carving? despite the terminology it’s not going to be a full roast dinner; unless you have an appetite for data which as you’re here I’m assuming you have.

The TL;DR of “what is file carving” is taking a target blob of data (often a multi GB / TB file) and reducing it in to targeted pieces of data, this could be for instance grabbing all the jpeg images in a packet capture / mysqldump; or pulling that single table/schema out of a huge mysqldump with –all-databases (if you’re not using mydumper you really …

Background on Backup Locks

I was very excited to see Backup locks support in release notes for the latest Percona XtraDB Cluster 5.6.21 release. For those who are not aware, backup locks offer an alternative to FLUSH TABLES WITH READ LOCK (FTWRL) in Xtrabackup. While Xtrabackup can hot-copy Innodb, everything else in MySQL must be locked (usually briefly) to get a consistent snapshot that lines up with Innodb. This includes all other storage engines, but also things like table schemas (even on Innodb) and async replication binary logs. You can skip this lock, but it isn’t …

A few years ago Peter Zaitsev, in a post titled “To UUID or not to UUID,” wrote: “There is timestamp based part in UUID which has similar properties to auto_increment and which could be used to have values generated at same point in time physically local in BTREE index.”

For this post I’ve rearranged the timestamp part of UUID (Universal Unique Identifier) and did some benchmarks.

Many people store UUID as char (36) and use as row identity value (PRIMARY KEY) because it is unique across every table, every database and every server and allow easy merging of records from different databases. But here comes the problem, using it as PRIMARY KEY causes the problems described below.

Problems with UUID

• UUID has 36 characters which makes it bulky.
• InnoDB stores data in …

HAProxy is frequently used as a software load balancer in the MySQL world. Peter Boros, in a past post, explained how to set it up with Percona XtraDB Cluster (PXC) so that it only sends queries to available nodes. The same approach can be used in a regular master-slaves setup to spread the read load across multiple slaves. However with MySQL replication, another factor comes into play: replication lag. In this case the approach mentioned for Percona XtraDB Cluster does not work that well as the check we presented only returns ‘up’ or ‘down’. We would like to be able to tune the weight of a replica inside HAProxy depending on its replication lag. This is what we will do in this post using HAProxy 1.5.

Agent …