Many people have a master/slave MySQL environment of various different topologies, and many use the slave as a backup.
Is your slave schema identical to your production schema? As long as an SQL statements completes without an error, your slave schema can differ. Common examples are different indexes or storage engines for example. However if you use the slave as backup, you want to ensure when you recover, you are recovering a production environment, not a slave environment.

While the changes may be small, the can lead to different results. For a client I found that the default value of a price field was 10.00 in one schema and 0.00 in another. Not withstanding using defaults for important fields and not defining in an INSERT is a different issue, it highlighted the different schemas can easily exist.

My tool of choice is SchemaSync. The reason why I like this command is …

A new healthcare project in Zambia is trying to integrate supervisors, clinics, and community healthcare workers (CHW) into a system that can improve patient service and provide more data about the effectiveness of care. Because of the technical challenges in an extreme rural setting, unique solutions are required. According to Cory Zue, chief technology officer of Dimagi, CouchDB went a long way toward keeping a consistent set of records under extreme circumstances. The full story will be laid out in Zue's talk at the upcoming MySQL conference, but here's a sneak peak.

You're involved with a …

How this happens or who does it is obviously a larger and more complex conversation however it is better then involving innocent animals.

How is it that trivial $#*! gets voted and has a string of comments I can not explain, however Planet MySQL should have practical MySQL related content. I would vote for the front page and RSS feed to show only moderated content, and content that did not pass the cut (and there is a lot of this) can be available on a less important page if necessary.

Rather then complaining like many open source communities, let us propose a way to improve the system we use.

Running a MySQL backup and ensuring it completed successfully and backup files exist is not enough. In my B&R Quiz from Checked your MySQL recovery process recently? one important step is “Do you review your backup logs EVERY SINGLE day or have tested backup monitoring in place?”

This is what I found when reviewing a backup log for a client today.

mysqldump: Got error: 1142: SELECT,LOCK TABL command denied to user 'root'@'localhost' for table 'cond_instances' when using LOCK TABLES
mysqldump: Got error: 1142: SELECT,LOCK TABL command denied to user 'root'@'localhost' for table 'cond_instances' when using LOCK TABLES

The backup script was completing, backup files were in place (and are listed in the log file) however these errors were occurring.

Further investigation was less then one minute of …

Netflix went down over three hours ago, and everyone is on edge here. My son just started reciting the script to "Monty Python and the Holy Grail" in an attempt to keep our courage up. This may be the last thing I ever write, so — Oh, never mind, it's back up again ... Crisis averted, and on to this week's developer news.

We have an App Store Appstore for that!

Amazon this week unleashed their own Appstore for Android devices. Apple took umbrage at the use of the (evidently trademarked) term "App Store" and fired a salvo of …

This was a request yesterday on a mailing list about how to I block DROP statements from running on a slave. There were responses including MySQL could not do this, or try other replication technologies however I thought I would share how you can easily do this on a slave.

You simply deny access on the slave. It is as simple as changing the MySQL privileges for the user(s) in question to remove DROP or ALTER capabilities.

Of course this will break replication rather then simply ignore the statement however I suspect that is the intended goal anyway. The first statement that uses the table will fail regardless. With appropriate monitoring of replication you should know in about 15 seconds. (Hint: If you don’t monitor replication or monitor it frequently, DO SO NOW!)

These leads to the question, what if the statements are legitimate? There are several solutions. Enable the specific privileges on the slave when the DBA …

Topology Participating hosts

* 1x BIG-IP VE
* 1x Debian Squeeze “Provisioning Server” serving DHCP, TFTP & DNS
* 3x Nortel/Avaya 1120E hard phones flashed to SIP1120e04.01.13.00
* 2x Debian Squeeze + digium asterisk packages:

$ grep asterisk /etc/apt/sources.list
deb http://packages.asterisk.org/deb squeeze main
deb-src http://packages.asterisk.org/deb squeeze main

DUNDi

*CLI> module reload pbx_dundi.so
*CLI> dundi show peers
*CLI> dundi show mappings
*CLI> dundi lookup 4012@extensions bypass
*CLI> dundi set debug on

SIP

*CLI> sip show peers

dialplan

*CLI> dialplan show RegisteredDevices

Work in progress

Yesterday, I installed a trixbox virtual machine using the …

Various people have complained about Linux swapping unexpectedly on boxes running mysqld, when apparently mysqld was not using all the memory and there was quite a bit of free memory available.

There’s also an article by Jeremy Cole. However, his solution requires a one-line change to mysqld_safe which while it’s small does not work very well if you have to maintain a large number of servers and are using packages asa package upgrade will overwrite the modified file mysqld_safe and then restart mysqld with the unmodified script. This leads to the need to repatch the script and then restart mysqld. Not very helpful.

So I was looking for another solution and came up with this option which basically requires a minor change to /etc/my.cnf and the use of a small shell wrapper script. The change to my.cnf is simply to …

I am one of the crazy individuals(*) that will be speaking at both the regular O’Reilly MySQL Conference and the IOUG Collaborate conference both being held in the second week of April. My 4 presentations are:

• Monday 3:45-4:45pm in Orlando – Common MySQL Scalability Mistakes
• Wednesday 2:00-3:00pm in Santa Clara – Add to Your O’Reilly Schedule – Best Practices for MySQL DBAs and Developers Part 1
• Wednesday 3:05-3:50pm in Santa Clara – …

For all those in New York this is an upcoming MySQL presentation held in conjunction with our colleagues at General Assembly on March 22nd 2011.

This presentation “How Better Indexes Save You Money” will be discussing how one simple technique can result in huge MySQL performance improvements and with zero code changes necessary. Many people think they know indexes, however MySQL and MySQL Storage Engines have some specifics that differ from more traditional RDBMS products. Learn some of the key analysis and verification techniques and be able to see immediate potential results in performance.

You can find more details at Meetup.com EffectiveMySQL. This new group is all about highly technical MySQL related content “no fluff, just stuff”.