Recently, one of our support customers faced this: “[ERROR] mysqld: Sort aborted: Server shutdown in progress.” At first it would appear this occurred because of a mysql restart (i.e. the MySQL server restarted and the query got killed during the stopping of mysql). However, while debugging this problem I found no evidence of a MySQL server restart – which proves that what’s “apparent” is not always the case, so this error message was a bit misleading. Check this bug report for further details http://bugs.mysql.com/bug.php?id=18256 (it was reported back in 2006).

I found that there are two possible reasons for this error: Either the MySQL server restarts during execution of the query, or the query got killed forcefully during execution which utilizes the …

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 server overload” – having more work than the server can possibly handle. At this point I see people often jumping to the conclusion that something went wrong with MySQL and focus all their effort on this belief. This is also often how we see questions framed when they are filed with our Support or to Emergency Consulting.

In fact there are two very distinct causes for such a situation – and to find the resolution most effectively you need to understand what …

One of the routine tasks for a DBA is renaming database schemas, and as such MySQL added a command to carry out that purpose called “RENAME DATABASE <database_name>”. However this command just made it through a few minor releases before being discontinued (from MySQL 5.1.7 to 5.1.23). Here’s a link to the reference manual regarding the command http://dev.mysql.com/doc/refman/5.1/en/rename-database.html. Vadim wrote a MySQL Performance Blog post about this a few years ago where he mentions the dangerous nature of this command – that post was appropriately headlined, “Dangerous Command.” Today we will see what are the ways in which a database schema can be renamed and which of them is the quickest.

Method 1: A …

Recently I was working with a customer where we noticed that Seconds_Behind_Master fluctuating from an expected value of 0 seconds behind to a fairly high six figure value.  The servers were configured in a master-master relationship and used 5 figure server_id values, and we had just migrated this cluster from one data centre to another by re-pointing masters.  Seeing large fluctuations in Seconds_Behind_Master can often be explained by long running queries being processed by the SQL_THREAD, however SHOW PROCESSLIST indicated that there were no long running replication events, and we had no other indication that the server was lagging  due to resource constraints — CPU, disk, and memory were under-utilized.

We then moved our investigation to manual review of the binary log where events appeared normal (5 digit server_id values) until every once in a while we would see a rash of server_id 21 events.. Wait, what?  I …

While troubleshooting deadlocks for a customer, I came around an interesting situation involving InnoDB gap locks. For a non-INSERT write operation where the WHERE clause does not match any row, I expected there should’ve been no locks to be held by the transaction, but I was wrong. Let’s take a look at this table and and example UPDATE.

mysql> SHOW CREATE TABLE preferences \G
*************************** 1. row ***************************
       Table: preferences
Create Table: CREATE TABLE `preferences` (
  `numericId` int(10) unsigned NOT NULL,
  `receiveNotifications` tinyint(1) DEFAULT NULL,
  PRIMARY KEY (`numericId`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)
mysql> BEGIN;
Query OK, 0 rows affected (0.00 sec)
mysql> SELECT COUNT(*) FROM preferences;
+----------+
| COUNT(*) |
+----------+
|        0 |
+----------+
1 row in set …

I’m looking forward to next week’s MySQL webinar with Robert Hodges, CEO of Continuent. We’ll be speaking on the topic “Multi-Data Center MySQL with Continuent Tungsten.”

You’re not alone if you’ve been vexed when trying to assemble multi-master, multi-site MySQL clusters. Whether that was a move from a single database server to a scalable cluster, or from a brittle MySQL replication system to a transparent, manageable database cluster.

We’ve all been there at one point or another in our careers. So learn from our experience. In our joint webinar next week (Dec. 11), Robert and I will …

INFORMATION_SCHEMA is usually the place to go when you want to get facts about a system (how many tables do we have? what are the 10 largest tables? What is data size and index size for table t?, etc). However it is also quite common that such queries are very slow and create lots of I/O load. Here is a tip to avoid theses hassles: set innodb_stats_on_metadata to OFF.

This is a topic we already talked about, but given the number of systems suffering from INFORMATION_SCHEMA slowness, I think it is good to bring innodb_stats_on_metadata back on the table.

The problem

Let’s look at a system I’ve seen recently: MySQL 5.5, working set fitting in memory but not the whole dataset, around 4000 InnoDB tables.

The I/O load is very light as …

We have always received quite few questions here at Percona Support on how to avoid the dreaded “Too many connections” error, as well as what is the recommended value for max_connections. So, in this article I will try to cover best possible answers to these questions so others can mitigate similar kinds of issues.

My colleague Aurimas wrote a wonderful post some time back about changing max_connections value via GDB when MySQL server is running to get rid of the “Too many connections” error without restarting MySQL. You can check here for details.

By default 151 is the …

Recently, I helped a client that was having issues with deployments causing locking in their production databases.  At a high level, the two key components used in the environment were:

• Capistrano (scripted deployments) [website]
• Liquibase (database version control) [website]

At a high level, they currently used a CLI call to Liquibase as a sub-task within a larger deployment task.  The goal of this engagement was to modify that sub-task to run Liquibase in a non-blocking fashion as opposed to the default that just runs native ALTERS against the database.

As I wasn’t very familiar with Liquibase, I took this opportunity to learn more about it and it seems like a very valuable tool.  Essentially, it does the following:

• Adds two version control tables to …

This is part two on a two-part series on the performance implications of in-flight data encryption with MySQL. In the first part, I focused specifically on the impact of using MySQL’s built-in SSL support with some rather surprising results. Certainly it was expected that query throughput would be lower with SSL than without, but I was rather surprised by the magnitude of the performance hit incurred at connection setup time. These results naturally lended themselves to some further investigation; in particular, I wanted to compare performance differences between MySQL’s built-in SSL encryption facilities and external encryption technologies, such as SSH tunneling. I’ll also be using this post to address a couple of questions posed in the comments on my original article. So, without further ado….

Test Environment

The …