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10 Newer Entries Showing entries 31 to 40 of 73 10 Older Entries

Displaying posts with tag: configuration (reset)

MMM for MySQL single reader role
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The standard documentation and tutorials on MMM for MySQL, for master-master replication setup, suggest one Virtual IP for the writer role, and two Virtual IPs for the reader role. It can be desired to only have a single virtual IP for the reader role, as explained below.

The two IPs for the reader role

A simplified excerpt from the mmm_common.conf sample configuration file, as can be found on the project’s site and which is most quoted:

<host db1>
  mode                    master
  peer …
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Reviewing your MySQL installation on Oracle Enterprise Linux
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After successfully Installing MySQL, let us take a look at an operational MySQL instance on your Oracle Enterprise Linux server.

User Management

By default there will be a new mysql user and group created. This user is used to run the mysqld process is generally not used for any other purpose.

$ grep mysql /etc/{passwd,shadow,group}
/etc/passwd:mysql:x:27:27:MySQL Server:/var/lib/mysql:/bin/bash
/etc/group:mysql:x:27: …
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Verifying GROUP_CONCAT limit without using variables
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I have a case where I must know if group_concat_max_len is at its default value (1024), which means there are some operation I cannot work out. I’ve ranted on this here.

Normally, I would simply:

SELECT @@group_concat_max_len

However, I am using views, where session variables are not allowed. Using a stored function can do the trick, but I wanted to avoid …

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Those oversized, undersized variables defaults
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Some mysqld parameters are far from having reasonable defaults. Most notable are the engine-specific values, and in particular the InnoDB parameters.

Some of these variables have different defaults as of MySQL 5.4. innodb_buffer_pool_size, for example, is 128M on 5.4. innodb_log_file_size, however, has changed back and forth, as far as I understand, and is down to 5M again. These settings are still the same on 5.5.

I wish to present some not-so-obvious parameters which, in my opinion, have poor defaults, for reasons I will explain.

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Replication configuration checklist
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This post lists the essential and optional settings for a replication environment.

It does not explain how to create replicating slaves. See How To Setup Replication for that. However, not all configuration options are well understood, and their roles in varying architectures can change.

Here are the settings for a basic Master/Slave(s) replication architecturee.


  • log-bin: enable binary logs on the master. Replication is based on the master logging all modifying queries …
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Kontrollkit – new version available for download
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Just a quick notice to let everyone know that there is a new version of Kontrollkit available. There are some required bug fixes to the formerly new python backup script and some Solaris compatible changes to the various my.cnf files. You can download the new version here:, or here:

Tuning your Cluster with ndbinfo (7.1) part 1 of X
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The new ndbinfo interface in 7.1 is really useful to assist in tuning MySQL Cluster. Here is an example (more will follow):

I started with one test where I inserted two blobs (1KB + 1KB) in one table.
From 16 threads (colocated with one mysqld, two data nodes, separate computers) and one application driving the load I reached about 6960TPS, and the utilization of the redo buffers (controlled by the parameter RedoBuffer in config.ini) looked like:

mysql< select * from ndbinfo.logbuffers;
| node_id | log_type | log_id …

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But I DO want MySQL to say “ERROR”!
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MySQL is known for its willingness to accept invalid queries, data values. It can silently commit your transaction, truncate your data.

  • Using GROUP_CONCAT with a small group_concat_max_len setting? Your result will be silently truncated (make sure to check the warnings though).
  • Calling CREATE TEMPORARY TABLE? You get silent commit.
  • Issuing a ROLLBACK on non-transactional involved engines? Have a warning; no error.
  • Using LOCK IN SHARE …
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Building MySQL Server with CMake on Linux/Unix
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CMake is a cross-platform, open-source build system, maintained by Kitware, Inc.

From the home page:

CMake is a family of tools designed to build, test and package software. CMake is used to control the software compilation process using simple platform and compiler independent configuration files. CMake generates native makefiles and workspaces that can be used in the compiler environment of your choice.

It has been used for …

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Quick reminder: avoid using binlog-do-db
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Nothing new about this warning; but it’s worth repeating:

Using binlog-do-db is dangerous to your replication. It means the master will not write to binary logs any statement not in the given database.

Ahem. Not exactly. It will not write to binary logs any statement which did not originate from the given database.

Which is why a customer, who was using Toad for MySQL as client interface to MySQL, and by default connected to the mysql schema, did …

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10 Newer Entries Showing entries 31 to 40 of 73 10 Older Entries

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