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10 Newer Entries Showing entries 61 to 70 of 16564 10 Older Entries

Displaying posts with tag: mysql (reset)

C bitfields considered harmful
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In C (and C++) you can specify that a variable should take a specific number of bits of storage by doing “uint32_t foo:4;” rather than just “uint32_t foo”. In this example, the former uses 4 bits while the latter uses 32bits. This can be useful to pack many bit fields together.

Or, that’s what they’d like you to think.

In reality, the C spec allows the compiler to do just about anything it wants with these bitfields – which usually means it’s something you didn’t expect.

For a start, in a struct -e.g. “struct foo { uint32_t foo:4; uint32_t blah; uint32_t blergh:20; }” the …

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Percona Live London 2014 Wrap Up
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The 2014 edition of Percona Live London brought together attendees from 30 countries to hear insightful talks from leaders in the MySQL community. The conference kicked off on Monday with a full day of tutorials followed by the very popular Community Dinner featuring a double decker bus shuttle from the conference to the event.

Tuesday started with keynote talks by representatives from MySQL, VMware, HGST, Codership, and Percona. I particularly enjoyed the talks by Tomas Ulin of MySQL (which highlighted the upcoming …

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Everything about MySQL Users and Logins You Didn’t Know and Were Afraid to Ask
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Logging into a MySQL server is generally dead simple—supply a username, a password, and you’re all set!

There are, however, more complex use cases such as when making use of our Enterprise Authentication plugins. It’s also sometimes helpful to have a more detailed understanding of what happens “under the hood”. So I’ll attempt to lift the hood and walk you through all of the nitty-gritty details regarding exactly just what happens when you log into a MySQL server.

Firstly, there are no less than 4 “users” involved in the authentication process. And a distinction between a user id and a user account exists. And it gets more and more …

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volatile considered harmful
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While playing with MySQL 5.7.5 on POWER8, I came across a rather interesting bug (74775 - and this is not the only one… I think I have a decent amount of auditing and patching to do now) which made me want to write a bit on memory barriers and the volatile keyword.

Memory barriers are hard.

Like, super hard. It’s the kind of thing that makes you curse hardware designers, probably because they’re not magically solving all your problems for you. Basically, as you get more CPU cores and each of them have caches, it gets more expensive to keep everything in sync. …

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You can use MySQL for Visual Studio in Visual Studio 2013 Community edition
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A lot a great announcements were done today at the Visual Studio Connect event. And one of the things we are more excited about is hearing that there is a new edition of Visual Studio: Visual Studio 2013 Community.

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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Preliminary MySQL Cluster benchmark results on POWER8
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Yesterday, I got the basics going for MySQL Cluster on POWER. Today, I finished up a couple more patches to improve performance and ran some benchmarks.

This is on a 3.7Ghz POWER8 machine with non-balanced memory (only 2 of the 4 NUMA nodes have memory, so we have less total memory bandwidth than we could have, plus I’m going to bind ndbmtd to the CPUs in these NUMA nodes)

With a setup of a single replica and two data nodes on the one machine (each bound to a specific NUMA node), running the flexAsync benchmark …

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Discussing the innodb_log_block_size variable
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Not a ground-breaking post here, but if you are interested in knowing more about the innodb_log_block_size variable, or if you use SSD cards and/or large InnoDB log files on ext4, then this is for you.

I’d read about it before briefly before, but didn’t give it too much thought until I ran across the following entry in an error log the other day:

InnoDB: Warning: innodb_log_block_size has been changed
from default value 512. (###EXPERIMENTAL### operation)

This got me wanting to know more.

Basically, this variable changes the size of transaction log records. Generally, the default of 512 is a good value. However, …

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MySQL Cluster on POWER8
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So, I’ve written previously on MySQL on POWER, and today is a quick bit of news about MySQL Cluster on POWER – specifically MySQL Cluster 7.3.7.

I ran into three main issues in getting some flexAsync benchmark results. One of them was the fact that I wanted to do this in the middle of all the POWER8 machines I usually use moving buildings (hard to run benchmarks when computers are packed up in boxes on a truck).

The next issue was that ndbmtd (the multi-threaded data node) needs memory barriers for the magic message passing stuff between threads. So, that’s pretty easy (about an eight line patch).

The next issue was in the …

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The Story of One Contribution
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The MySQL Server 5.7.5 Development Milestone Release includes support for acquiring multiple user-level locks within the same connection. The implementation of this feature is based on a contributed patch by Konstantin Osipov. This post tells the story about what happened with this patch on its way into the MySQL Server codebase.

If you are more interested in using this new functionality and the feature itself, rather than in the history behind it, then it is better to simply read the …

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10 Newer Entries Showing entries 61 to 70 of 16564 10 Older Entries

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