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Showing entries 1 to 10 of 18 8 Older Entries

Displaying posts with tag: Stéphane Combaudon (reset)

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?

  • The replication
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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 address, hence the issue.

Let’s edit /etc/rsyslog.conf and uncomment these lines:

$ModLoad imudp
$UDPServerRun 514

This will make rsyslog listen on UDP port 514 for all IP

  [Read more...]
MySQL & OpenStack: How to overcome issues as your dataset grows
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MySQL is the database of choice for most OpenStack components (Ceilometer is a notable exception). If you start with a small deployment, it will probably run like a charm. But as soon as the dataset grows, you will suddenly face several challenges. We will write a series of blog posts explaining the issues you may hit and how to overcome them.

Where is MySQL used in OpenStack?

Have a look at the logical diagram of OpenStack below (click the image for a larger view).

 

The diagram is a bit

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Using MySQL 5.6 Global Transaction IDs (GTIDs) in production: Q&A
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Thank you to all of you who attended my webinar last week about Global Transaction IDs (GTIDs), which were introduced in MySQL 5.6 to make the reconfiguration of replication straightforward. If you missed my webinar, you can still listen to the recording and download the sides (free). We had a lot of questions during the webinar, so let me try to answer them here. Please let me know in the comments if additional

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How to use MySQL Global Transaction IDs (GTIDs) in production
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Reconfiguring replication has always been a challenge with MySQL. Each time the replication topology has to be changed, the process is tedious and error-prone because finding the correct binlog position is not straightforward at all. Global Transaction IDs (GTIDs) introduced in MySQL 5.6 aim at solving this annoying issue.

The idea is quite simple: each transaction is associated with a unique identifier shared by all servers in a given replication topology. Now reconfiguring replication is easy as the correct binlog position can be automatically calculated by the server.

Awesome? Yes it is! However GTIDs are also changing a lot of things in how we can perform operations on replication. For instance,

  [Read more...]
How to use MySQL Global Transaction IDs (GTIDs) in production
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Reconfiguring replication has always been a challenge with MySQL. Each time the replication topology has to be changed, the process is tedious and error-prone because finding the correct binlog position is not straightforward at all. Global Transaction IDs (GTIDs) introduced in MySQL 5.6 aim at solving this annoying issue.

The idea is quite simple: each transaction is associated with a unique identifier shared by all servers in a given replication topology. Now reconfiguring replication is easy as the correct binlog position can be automatically calculated by the server.

Awesome? Yes it is! However GTIDs are also changing a lot of things in how we can perform operations on replication. For instance, skipping

  [Read more...]
Monitoring MySQL flow control in Percona XtraDB Cluster 5.6
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Monitoring flow control in a Galera cluster is very important. If you do not, you will not understand why writes may sometimes be stalled. Percona XtraDB Cluster 5.6 provides 2 status variables for such monitoring: wsrep_flow_control_paused and wsrep_flow_control_paused_ns. Which one should you use?

What is flow control?

Flow control does not exist with regular MySQL replication, but only with Galera replication. It is simply the mechanism nodes are using when they are not able to keep up with the write load: to keep replication synchronous, the node that is starting to lag instructs the other nodes that writes should be paused for some time so it does not get too far behind.

If you are not familiar with this notion, you

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Failover with the MySQL Utilities – Part 1: mysqlrpladmin
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MySQL Utilities are a set of tools provided by Oracle to perform many kinds of administrative tasks. When GTID-replication is enabled, 2 tools can be used for slave promotion: mysqlrpladmin and mysqlfailover. We will review mysqlrpladmin (version 1.4.3) in this post.

Summary

  • mysqlrpladmin can perform manual failover/switchover when GTID-replication is enabled.
  • You need to have your servers configured with --master-info-repository = TABLE or to add the --rpl-user option for the
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Errant transactions: Major hurdle for GTID-based failover in MySQL 5.6
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I have previously written about the new replication protocol that comes with GTIDs in MySQL 5.6. Because of this new replication protocol, you can inadvertently create errant transactions that may turn any failover to a nightmare. Let’s see the problems and the potential solutions.

In short

  • Errant transactions may cause all kinds of data corruption/replication errors when failing over.
  • Detection of errant transactions can be done with the GTID_SUBSET() and
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GTIDs in MySQL 5.6: New replication protocol; new ways to break replication
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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

  [Read more...]
Showing entries 1 to 10 of 18 8 Older Entries

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