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10 Newer Entries Showing entries 31 to 40 of 395 10 Older Entries

Displaying posts with tag: Insight for DBAs (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?

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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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More then 1000 columns – get transactional with TokuDB
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Recently I encountered a specific situation in which a customer was forced to stay with the MyISAM engine due to a legacy application using tables with over 1000 columns. Unfortunately InnoDB has a limit at this point. I did not expect to hear this argument for MyISAM. It is usually about full text search or spatial indexes functionality that were missing in InnoDB, and which …

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MySQL upgrade best practices
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MySQL upgrades are necessary tasks and we field a variety of questions here at Percona Support regarding MySQL upgrade best practices. This post highlights recommended ways to upgrade MySQL in different scenarios.

Why are MySQL upgrades needed? The reasons are many and include: Access to new features, performance benefits, bug fixes…. However, MySQL upgrades can be risky if not tested extensively beforehand with your application because the process might break it, …

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Managing big data? Say ‘hello’ to HP Vertica
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Over the past few months, I’ve seen an increase in the following use case while working on performance and schema review engagements:

I need to store exponentially increasing amounts of data and analyze all of it in real-time.

This is also known simply as: “We have big data.” Typically, this data is used for user interaction analysis, ad tracking, or other common click stream applications. However, it can also be seen in threat assessment (ddos mitigation, etc), financial forecasting, and other applications as well. …

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Syncing MySQL slave table with pt-online-schema-change
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I recently encountered a situation in which after running Percona Toolkit’s pt-table-checksum on a customer system, 95% of the table on the MySQL master was different on the MySQL slave. Although this table was not a critical part of the infrastructure, from time to time, writes to the table from the master would break replication. Additionally, this table has about 6 million rows, and running pt-table-sync would take sometime. Rebuilding the slave from backup of the master would not be an easy option as well since the slave acts as an archive where it has a …

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OpenStack users shed light on Percona XtraDB Cluster deadlock issues
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I was fortunate to attend an Ops discussion about databases at the OpenStack Summit Atlanta this past May as one of the panelists. The discussion was about deadlock issues OpenStack operators see with Percona XtraDB Cluster (of course this is applicable to any Galera-based solution). I asked …

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Generating test data from the mysql> prompt
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There are a lot of tools that generate test data.  Many of them have complex XML scripts or GUI interfaces that let you identify characteristics about the data. For testing query performance and many other applications, however, a simple quick and dirty data generator which can be constructed at the MySQL command line is useful.

First, let’s talk about what kind of data you can easily create with MySQL function calls:

You can generate a decimal number between zero and another number using the MySQL RAND() function like the following query (here between 0 and 10000):

SELECT RAND() * 10000;

Similarly, …

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Multi-Valued INSERTs, AUTO_INCREMENT & Percona XtraDB Cluster
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A common migration path from standalone MySQL/Percona Server to a Percona XtraDB Cluster (PXC) environment involves some measure of time where one node in the new cluster has been configured as a slave of the production master that the cluster is slated to replace. In this way, the new cluster acts as a slave of the production environment – traditional replication takes care of getting the data into the cluster, and then Galera replication handles the intra-cluster traffic. This often works without issue, although there is one case that I’ve …

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How to calculate the correct size of Percona XtraDB Cluster’s gcache
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When a write query is sent to Percona XtraDB Cluster all the nodes store the writeset on a file called gcache. By default the name of that file is galera.cache and it is stored in the MySQL datadir. This is a very important file, and as usual with the most important variables in MySQL, the default value is not good for high-loaded servers. Let’s see why it’s important and how can we calculate a correct value for the workload of our cluster.

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10 Newer Entries Showing entries 31 to 40 of 395 10 Older Entries

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