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Displaying posts with tag: Databases (reset)
MySQL Quirk with Not Null Columns and Default Values

One of my coworkers came across a strange quirk in MySQL with default values for not null columns. Take a look at this table:

Create Table Posts
(
     PostID Int Auto_Increment Primary Key
    ,Title Varchar(30) Not Null
    ,Body Text Not Null
    ,Summary Varchar(25) Not Null Default ''
);

Note the column Summary that is marked not null but has a default value of an empty string. Now, try to insert a null value into this column.

Insert Into Posts (Title, Body, Summary) Values ('A title', 'A body', null);

You’ll get this error:

ERROR 1048 (23000): Column 'Summary' cannot be null

Now, using an extended insert (where you specify multiple rows in an insert statement), we can insert the same data and it will complete successfully, although there will be warnings.

Insert Into Posts (Title, Body, Summary) Values ('A title', 'A body', null), ('2nd body', '2nd body', null);

Query OK, 2 rows …
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A Different Spin On the max_allowed_packet Problem

Back in November, I filed MySQL bug 67448, talking about a different type of max_allowed_packet problem.

See, an application had put data into the database, but could not retrieve it without getting max_allowed_packet. With the help of some really smart community folks (named Jesper Hansen, Brandon Johnson and Shane Bester), we determined that MySQL actually has 2 different max_allowed_packet settings: client and server.

When you change the max_allowed_packet variable, you are changing the server variable if it is in [mysqld] and the client variable if it is in [client] or [mysql] or whatever client you have. As far as we can tell, there’s no way to actually view what the client variable is, as looking at both the session and global max_allowed_packet variable shows you the server variable.

If max_allowed_packet is not set by the client, it defaults to …

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ulimits and upgrading from Oracle MySQL 5.0 to Percona patched MySQL 5.1

After upgrading to Percona’s patched MySQL 5.1*, end users were having connectivity problems, and reporting errors such as:

OperationalError: (2003, "Can't connect to MySQL server on 'db-amo-ro' (110)")

TimeoutError: Request timed out after 5.000000 seconds

OperationalError: (1135, "Can't create a new thread (errno 11); if you are not out of available memory, you can consult the manual for a possible OS-dependent bug")

We had these same problems a while back, before increasing ulimit settings in /etc/sysconfig/mysqld. Oracle’s MySQL startup script specifically sources this file:

[ -e /etc/sysconfig/$prog ] && . /etc/sysconfig/$prog

However, we saw these errors again when we upgraded to Percona’s MySQL 5.1. At first we thought that it was because Oracle’s startup script is /etc/init.d/mysqld and …

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MySQL User Group Video – Determinism and Databases

The May Boston MySQL User Group featured John Hugg of VoltDB talking about determinism and databases. I have uploaded the hour-long video to http://www.youtube.com/watch?v=mTDLyRauJtw. Seasoned MySQLers will nod their heads because the problems described are familiar, and those who are not exactly sure what “determinism and databases” means will learn a lot.

Enjoy!

(As always, videos are free on YouTube with no login or attempt to solicit your e-mail address or any other information)

Upgrading support.mozilla.org databases

A while ago (November 2012 to be exact), we upgraded the support.mozilla.org databases from Percona 5.1 to MariaDB 5.5 (the next step, happening soon, is upgrading them to Oracle’s MySQL 5.6). One of the engineers and I had a conversation where he mentioned that “one of our worst performing views on SUMO is doing waaaayyy better with the upgraded databases”, that it “seems more stable” and that “I stopped receiving ‘MySQL went away or disconnected emails’ which came in once in a while.”

It’s always nice to see upgrades actually making a difference. In our case we saw a lot less CPU wait, though that might also be partially due to tuning the memory settings on the machines and adding in another read slave to handle queries. As a result, network traffic throughput went from less than 1 Mb/sec to about 18 Mb/sec, because the machines were just handling more queries per second, period.

(I had this e-mail as a draft …

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Percona Ireland??

Anybody else noticed that Percona appears to not be a US entity any more?

I observed it today.

$ sudo /usr/bin/innobackupex ...
InnoDB Backup Utility v1.5.1-xtrabackup; Copyright 2003, 2009 Innobase Oy
and Percona Ireland Ltd 2009-2012.  All Rights Reserved.

This software is published under
the GNU GENERAL PUBLIC LICENSE Version 2, June 1991.

In previous versions this did say Percona Inc, 2009-2012.

The footer of the Documentation also states © Copyright Percona Ireland Ltd. 2009-2013.

Women in Science and Engineering (WISE) Computing Skills Boot Camp

Software Carpentry is running a 2-day software skills boot camp in Boston, June 24-25th 2013, for women in science, engineering, medicine, and related research
areas. Registration is $20.

Boot camps alternate short tutorials with hands-on practical exercises. You are taught tools and concepts you can use immediately to increase your productivity and improve confidence in your results. Topics covered include the Unix shell, version control, basic Python programming, testing, and debugging — the core skills needed to write, test and manage research software.

This boot camp is open to women at all stages of their research careers, from graduate students, post-docs, and faculty to staff scientists at hospitals and in the public, private, and non-profit sectors.

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On the threshold

When you setup a monitoring system for SQL Server, you often use thresholds to determine when an instance is healthy. You might say that you want to be alerted when CPU use is over 90% or when there’s only 10% of disk space left. The trouble with these thresholds is that they will often throw off false positives, or send you an alert when really nothing is wrong. Simple thresholds often have to be tuned to the individual instance, since a server with 10 TB still has 1 TB of space left at 90% disk use.

Baron Schwartz blogged about this issue in an article and he’s been creating software that monitors MySQL beyond simple thresholds, after stating that they do not work in most cases. He makes a good …

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Extending Reporting Services

I am doing a reporting proof-of-concept (POC) for my company. Business intelligence (BI) is often the last thing that gets thought of during an application’s life cycle because it’s only really necessary after you get customers. Before that, the main focus is on application features. Soon after launch, your coworkers and your customers start asking questions about usage and adoption, and customers start to ask for summary information on their data as well as just dumping their data. If you’re the only guy in charge of the database, this is often overwhelming.

Thankfully, we now have many options for what’s called self-service BI. The developer or DBA sets up the basic data models (say Orders) in an automated tool like SQL Server Reporting Services (SSRS) and then allows an information worker to select the columns, perform joins, and add filters to create reports. This basically cuts down miscommunication that can often happen between …

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From Oracle to 10gen, The MongoDB Company

Those who are familiar with me know I've a dream.

5 years ago I decided to leave a systems integrator where I was doing great. Why? I wanted to be in a company with the same growth prospects that Oracle had in the 80s. I dreamed to be in the Oracle of 30 years ago and, as time travel wasn't affordable, I decided to join MySQL AB to help expand the business in Europe, the Middle East and Africa.
A few years later my dream came true, but in a slightly different sense. Sun acquired MySQL and was later swallowed by Oracle giving me the opportunity to join the company I wished I could have helped build.

Oracle is an amazing …

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