One question I often get is how one can find out queries which should be optimized. By looking at pt-query-digest report it is easy to find slow queries or queries which cause the large portion of the load on the system but how do we know whenever there is any possibility to make this query [...]
When is MIN(DATE) != MIN(DATE) ?
September 4, 2012 By 5 Comments
Inspiration for this post is courtesy of a friend and former colleague of mine, Greg Youngblood, who pinged me last week with an interesting MySQL puzzle. He was running Percona Server 5.5.21 with a table structure that looks something like this:
1 2 3 4 5 6 7 8 9 | CREATE TABLE foo ( id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY, uid INT UNSIGNED NOT NULL, update_time DATETIME NOT NULL, .... INDEX `uid` (uid, update_time), INDEX `bar` (some_other_columns) .... ) ENGINE=InnoDB; |
When he ran this query:
1 | SELECT MIN(update_time) FROM foo WHERE update_time IS NOT NULL AND update_time <> '0000-00-00 00:00:00'; |
The result came back as 2012-06-22 10:28:16. [...]
Make your file system error resilient
August 24, 2011 By 8 Comments
One of the typical problems I see setting up ext2/3/4 file system is sticking to defaults when it comes to behavior on errors. By default these filesystems are configured to Continue when error (such as IO error or meta data inconsistency) is discovered which can continue spreading corruption. This manifests itself in a worst way [...]
Give me 8 hours, and I’ll help you build a better application
August 29, 2009 By 4 Comments
I have run into a number of cases recently that all had a similar look and feel. In most of these cases, the symptoms were very complicated, but they boiled down to just a few problems that can be prevented in very simple ways. If you are not doing any of the following three simple [...]
High-Performance Click Analysis with MySQL
December 22, 2008 By 13 Comments
We have a lot of customers who do click analysis, site analytics, search engine marketing, online advertising, user behavior analysis, and many similar types of work. The first thing these have in common is that they’re generally some kind of loggable event. The next characteristic of a lot of these systems (real or planned) is [...]
How adding another table to JOIN can improve performance ?
August 1, 2008 By 12 Comments
JOINs are expensive and it most typical the fewer tables (for the same database) you join the better performance you will get. As for any rules there are however exceptions The one I’m speaking about comes from the issue with MySQL optimizer stopping using further index key parts as soon as there is a range [...]
MySQL Replication vs DRBD Battles
April 28, 2008 By 12 Comments
Well these days we see a lot of post for and against (more, more) using of MySQL and DRBD as a high availability practice. I personally think DRBD has its place but there are far more cases when other techniques would work much better for variety of reasons. First let me start with Florian’s comments [...]
MySQL Error Message Nonsenses
March 16, 2008 By 7 Comments
What MySQL honestly was never good at is giving good helpful error messages. Start with basics for example – The error message in case of syntax error gives you information about tokens near by but little details:
1 2 | mysql> select * from user oder by pwd; ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'by pwd' at line 1 |
It would be much better if MySQL would give error give exact position of error (with complex [...]
Database problems in MySQL/PHP Applications
August 11, 2006 By 13 Comments
Article about database design problems is being discussed by Kristian. Both article itself and responce cause mixed feellings so I decided it is worth commenting: 1. Using mysql_* functions directly This is probably bad but I do not like solutions proposed by original article ether. PEAR is slow as well as other complex conectors. I [...]
Cache Performance Comparison
August 9, 2006 By 74 Comments
Jay Pipes continues cache experiements and has compared performance of MySQL Query Cache and File Cache. Jay uses Apache Benchmark to compare full full stack, cached or not which is realistic but could draw missleading picture as contribution of different components may be different depending on your unique applications. For example for application containing a [...]
