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Showing entries 1 to 10 of 373 10 Older Entries

Displaying posts with tag: Insight for DBAs (reset)

Sys Schema for MySQL 5.6 and MySQL 5.7
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Performance Schema (P_S) has been available since MySQL 5.5, more than 4 years ago. It is still difficult to see production servers with P_S enabled, even with MySQL 5.6 where the feature is enabled by default. There have been several complaints like the overhead, that the fix is a work in progress, and the ease of use. 52 tables to query and 31 configuration variables is enough to scare people.

There is a solution for the second problem, the usability. It’s name is “sys schema“. It is a collection of views, functions and procedures to make P_S more user friendly.

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How a set of queries can be killed in MySQL using Percona Toolkit’s pt-kill
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You might have encountered situations where you had to kill some specific select queries that were running for long periods and choking the database. This post will go into more detail with an example of report query offloading.

Report query (select) offloading to a slave server is a common practice to reduce the workload of the master DB server. The long running selects will be executed in the slave for report generation. I have observed in many cases where the slave used to get delayed or the slave DB encounters a slowdown due to some heavy long-running orphaned selects from some wrong reports.

There are two …

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Avoiding MySQL ALTER table downtime
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MySQL table alterations can interrupt production traffic causing bad customer experience or in worst cases, loss of revenue. Not all DBAs, developers, syadmins know MySQL well enough to avoid this pitfall. DBAs usually encounter these kinds of production interruptions when working with upgrade scripts that touch both application and database or if an inexperienced admin/dev engineer perform the schema change without knowing how MySQL operates internally.

Truths
* Direct MySQL ALTER table locks for duration of change (pre-5.6)
* Online DDL in MySQL 5.6 is not always online and may incurr locks
* Even with …


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Typical misconceptions on Galera Replication for MySQL
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Even if a Galera node looks like a regular MySQL server, the underlying replication mechanism is very different. This implies some changes in the way you have to configure the Galera nodes. Here are some of the most common misconceptions about Galera when using Percona XtraDB Cluster.

Q: Why should I enable binary logging as it is not needed by Galera replication?
Unlike for regular asynchronous MySQL replication, it is true that …

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RDS for Aurora unveiled at AWS re:Invent
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One of the big announcements at the Amazon Web Services re:Invent 2014 conference this week was the unveiling of Aurora. The result of years of internal work, Aurora, currently in preview, is a MySQL 5.6-compatible option that “combines the speed and availability of high-end commercial databases with the simplicity and cost-effectiveness of open source databases” on the AWS infrastructure. The Aurora database engine will be made available through the Amazon RDS for Aurora service. This new database option is another …

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Log rotate and the (deleted) MySQL log file mystery
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Did your logging stop working after you set up logrotate? Then this post might be for you.

Archive your log files!

Some time ago, Peter Boros wrote about Rotating MySQL Slow Logs safely, explaining the steps of a “best practice” log rotate/archive. This post will add more info about the topic.

When running logrotate for MySQL (after proper setting the /etc/logrotate.d/mysql conf file) from anacron, there’s a situation that you might potentially face if the user and password used to execute the …

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How to deal with MySQL deadlocks
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A deadlock in MySQL happens when two or more transactions mutually hold and request for locks, creating a cycle of dependencies. In a transaction system, deadlocks are a fact of life and not completely avoidable. InnoDB automatically detects transaction deadlocks, rollbacks a transaction immediately and returns an error. It uses a metric to pick the easiest transaction to rollback. Though an occasional deadlock is not something to worry about, frequent occurrences call for attention.

Before MySQL 5.6, only the latest deadlock can be reviewed using SHOW ENGINE INNODB STATUS command. But with Percona Toolkit’s …

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MySQL Replication: ‘Got fatal error 1236′ causes and cures
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MySQL replication is a core process for maintaining multiple copies of data – and replication is a very important aspect in database administration. In order to synchronize data between master and slaves you need to make sure that data transfers smoothly, and to do so you need to act promptly regarding replication errors to continue data synchronization. Here on the Percona Support team, we often help customers …

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MySQL ring replication: Why it is a bad option
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I’ve recently worked with customers using replication rings with 4+ servers; several servers accepting writes. The idea behind this design is always the same: by having multiple servers, you get high availability and by having multiple writer nodes, you get write scalability. Alas, this is simply not true. Here is why.

High Availability

Having several servers is a necessary condition to have high availability, but it’s far from sufficient. What happens if for instance C suddenly disappears?

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HAProxy: Give me some logs on CentOS 6.5!
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HAProxy is frequently used as a load-balancer in front of a Galera cluster. While diagnosing an issue with HAProxy configuration, I realized that logging doesn’t work out of the box on CentOS 6.5. Here is a simple recipe to fix the issue.

If you look at the top of /etc/haproxy/haproxy.cfg, you will see something like:

global
    log         127.0.0.1 local2
[...]

This means that HAProxy will send its messages to rsyslog on 127.0.0.1. But by default, rsyslog doesn’t listen on any …

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Showing entries 1 to 10 of 373 10 Older Entries

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