No space left on device – this can happen to anyone. Sooner or later you may face the situation where a database either has already or is only minutes away from running out of disk space. What many people do in such cases, they just start looking for semi-random things to remove – perhaps a backup, a few older log files, or pretty much anything that seems redundant. However this means acting under a lot of stress and without much thinking, so it would be great if there was a possibility to avoid that. Often there is. Or what if there isn’t anything to remove?

While xfs is usually the recommended filesystem for a MySQL data partition on Linux, the extended filesystem family continues to be very popular as it is used as default in all major Linux distributions. There is a feature specific to ext3 and ext4 that can help the goal of resolving the full disk situation.

…

The Helsinki MySQL User Group will meet at the usual place on May 29th. Click here for details and to RSVP. Linas Varbalas will talk about Tungsten and maybe dare a live demo!

Linas is in town for the OUGF Harmony conference 2012. The conference might of course be of some interest to user group members too. Due to the conference we also have other famous MySQLrs in town, Sheeri Kabral of OurSQLcast fame has also confirmed she will attend the user group (and maybe have OurSQLcast CD's with her?)

One of the very frequent cases with performance problems with MySQL is what they happen every so often or certain times. Investigating them we find out what the cause is some batch jobs, reports and other non response time critical activities are overloading the system causing user experience to degrade.

The first thing you need to know it is not MySQL problem, might be even not problem with your MySQL configuration, queries and hardware, even though fixing these does help in many cases. Whatever powerful and well tuned system you have if you put too heavy of concurrent load on it the response times will increase and user experience will suffer.

So what you can do to prevent this problem from happening ? The answer is easy. Throttle the side load so it does not consume too much system resources. Here are some specific techniques to use.

Do push concurrency too high Many developers will test script with …

The tools we’ve redesigned in Percona Toolkit recently have moved away from a legacy technique for operating on small numbers of rows at a time, towards a more reliable and predictable method. We call the old version “chunking” and the new version “nibbling.” Many other MySQL tools I’ve seen either operate on entire tables, or use the “chunking” technique and are exposed to the problems it creates. I’ll compare the two briefly to explain the differences.

Chunking attempts to divide a table into ranges of rows of a desired size, such as 1000 rows. It does this by examining the minimum and maximum value of the primary key (or other suitable index), estimating the number of rows in the table, and dividing one by the other to create a list of boundary values. Suppose that the minimum value is 1 and the maximum is 1000000, and there are an estimated 100000 rows in the table. The chunk boundaries will fall on intervals of 10000. …

The tools we’ve redesigned in Percona Toolkit recently have moved away from a legacy technique for operating on small numbers of rows at a time, towards a more reliable and predictable method. We call the old version “chunking” and the new version “nibbling.” Many other MySQL tools I’ve seen either operate on entire tables, or use the “chunking” technique and are exposed to the problems it creates. I’ll compare the two briefly to explain the differences.

I still continue to run benchmarks of different SSD cards. This time I show numbers for Virident FlashMAX 1400. This is a MLC PCIe SSD device. There are couple notes on these results.
First, this time I use a different server. For this benchmark it is Cisco UCS C250, while for previous results I used HP ProLiant DL380 G6.

Second note is, that I use a mode “turbo=1″ for Virident card. What does that mean? Apparently PCIe specification has a limitation on available power. If I am not mistaken it is 25W, however Virident to provide full write performance requires 28W. And while many servers can handle 28W on PCIe, this is a non-standard mode, and Virident by default uses 25W (turbo=0). To force full power, I load a driver with turbo=1. I also use “maxperformance” formatting for Virident, …

As an experiment, I have converted the MariaDB Bazaar repository into Git.

https://github.com/atcurtis/mariadb

Should be interesting...

The social network problem

Social networks like Facebook and Google+ have always been known as huge data mining machines and that they don’t have very strict privacy policies, meaning that:

• you are not informed what happens with your data (what it is used for) when you enter it,
• you don’t have full control over your data (deletion is very hard to impossible, you can’t rely that “deleted” data is really erased etc.),
• data may be given to third parties (like application providers) or wrong people without your (explicit) consent.

“Don’t use social networks” is not a solution in my opinion because social networks are media like any other media, and they have advantages (that’s why they shall – and will – be used) and dangers (that’s what should be minimized).

Diaspora – a solution?

So, I was very happy when I heard the first announcement of …

Happy Star Wars Day. May the Fourth be with you!

We are still busy with data center moves! Only two more to go through, until we are all done. Twice this week, people have come to me, frantically saying “This database is moving NEXT WEEK and I need it migrated! Help!” and in both instances my reply has been, “Those servers are ready to go, they’ve been replicating data for weeks.”

Which led coworker Shyam Mani to make a Chill Meme (has bad language), which then prompted me to make a Keep Calm Meme.

• Added some metadata for http://graphs.mozilla.org.
  
• Moved our internal …

This week we talk about MariaDB - explaining features, and comparing to Percona's patched MySQL and Oracle's MySQL. MariaDB is touted as "a better MySQL, not a different MySQL". MariaDB is the 2nd most popular open source database, even more popular than Postgres.

Conferences:
MySQL Innovation Day Schedule Tuesday June 5th, Redwood Shores, CA. Register here (free). Content will be available via live stream, so save the date!

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