As a former Oracle DBA, I know how the system and the database are linked.
The first one who told me that the installation of Oracle has never been a problem is a liar!
Yes, your database and your system are the best of friends, you must respect that.

I’d make a list of linux system settings to configure a MySQL databases server and share my sources with you.
In return, I would like you to share your sources with the community by publishing your tips in the comments.

swappiness

• This parameter allows to specify how the kernel must manage the memory swap
• Default value : 60 (Range 0 to 100)
• Value to set : 0 (it will swap only to avoid an out of memory condition)
• How to set a new non-persistent value :  sysctl -w vm.swappiness=0
• How to store a new persistent value : add …

Stating the problem.

In my job, I do a lot of testing. And no matter how much organized we try to be, we end up with fewer machines than we would need to run all the tests that we want.

For some tasks, we can run MySQL Sandbox, and get the job done. But sometimes we need to make sure that applications and systems work well across the network, and we need to install and run systems on separate servers.

However, when you test replication systems, and every cluster takes three or four servers, you run our of available hosts very quickly. So you decide to use the clusters that are dedicated to automated testing to also run your own manual tests. Soon you realize that the tests that you are running manually are clashing with the automated ones, or with the ones that your colleagues are running.

A simple solution is installing additional sandboxes for the MySQL …

I’m sure that many of you use the magic query from Shlomi.
This query retrieves the difference between two status values with a single query.
I’m really fan of this kind of query and about this query in particular. This query is very useful to retrieve an information without to have to store a middle result.

Now, I tried this query on a MariaDB 5.5 server and I had a surprise :

The result was a bit strange, with negative or null values.

I’ve just had these server for few hours in my hands and I had no more time to analyze the situation.
I assume that the subquery optimisations in MariaDB can be involve here but it’s just an assumption.

Does anyone encountered the …

A beautiful picture is sometimes better than words :

With standard HDDs (here in RAID 10), the innodb_io_capacity variable may have non expected effects.

You can see on this picture the result of a test on one of my server with only the replication thread activated. The value of the innodb_io_capacity variable was the single modification during the period.

So, don’t touch this parameter without a strong reason…
(Of course 30000 was a bit snooty)

[MAJ 2013-01-08] : I know 30k is a too high value for innodb_io_capacity, I used this value to make the graphe really eloquent.
Read this excellent post from Chris for more details : http://www.chriscalender.com/?p=201

…

I wish you all my best wishes for this new year.
I hope 2013 will be as exciting as 2012 for the MySQL community.

Thank you for spending time on MySQL[Plus] in 2012, I hope to have more and more readers in 2013.

If you would like to read (or read back) my posts published in 2012, here is the summary :

• How to quickly identify queries with pt-query-digest and pt-query-advisor from rules?
• A (little) MySQL bug story…
• Temporary file behavior… (and how lsof save my life) …

While testing MySQL 5.6, I came across some curious values for the new values used to set the crash-safe slave tables. To get safety, we need to set relay_log_info_repository and master_info_repository to 'TABLE'. That way, the replication information, instead of going to a file, will be saved to two tables in the mysql schema (mysql.slave_relay_log_info and mysql.slave_master_info).

So I was setting these values back and forth between 'FILE' and 'TABLE', until I made a "mistake." Instead of typing

set global relay_log_info_repository='table';

I wrote

set global relay_log_info_repository=1;

To my surprise, it did what I …

I would like to make a quick MySQL 101 about numeric types in MySQL and especially explain the difference between the numeric type attributes and the maximum value that a numeric type can store.

Someone asked me yesterday why when he inserts a value in a table, the value 127 appears instead of the value 160 that he’s just inserted.
Ok, let me explain, consider this table :

What happens if you want to insert this row in the table :

sql > insert into product values (160, 554, "iPad mini");
Query OK, 1 row affected, 1 warning (0.01 sec)
sql > show warnings;
+---------+------+---------------------------------------------+
| Level   | Code | Message                                     |
+---------+------+---------------------------------------------+
| Warning | 1264 | Out of range value for column 'id' at row 1 | …

I’m currently working on a new project about the explain command output.
For my research I’ve read a lot of documentations, presentations and blog posts and I would like to focus on the join type in the explain output.
And in particular when type=index in this explain output.

Take a look at what says the official documentation about type=index :

Wait a second, only the index tree is scanned? really?
This description seems to be the definition of a covering index.
But a covering index is only characterized by a “Using index” in the extra column of the explain output.

Consider the t1 table, just …

For the first time since the beginning of my long long career, I decided today to use an advice tool to check my MySQL configuration.

I decided to launch pt-variable-advisor and mysqltuner V2 on one of my MySQL server.
Here are the result outputs :

Then I ask myself what to do with these results, just raw results without much explanations, these tools are supposed to be done for beginners…

Just one example from mysqltuner : Too many temporary tables are being written to disk.  Increase max_heap_table_size and tmp_table_size
If I set the size of my temporary tables at 16Mb, what that’s means, I have to increase to 32Mb, 64Mb or more ?
…

I really like the percona toolkit, we all love the percona toolkit.
I know how it’s difficult to write operational and efficient scripts (I try to do that myself everyday)
And it is even more difficult to share a script, to take the responsibility to share its own code.
From there, understand that this article is simply a review of my own thoughts about pt-archiver (with the invaluable assistance of @maximefouilleul), I don’t want to question the quality or usefulness of this tool.

I tried pt-archiver for the first time this week, and the first thing I do before using a tool is read the documentation (yes, I really like to read documentations)

I was intrigued by some options of this tool, first, I can read “It deletes data from the source by default“.
Personally, I hate that you want to remove my data by default, I prefer to have a –delete option …