November 23, 2014

When is MIN(DATE) != MIN(DATE) ?

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:

When he ran this query:

The result came back as 2012-06-22 10:28:16. […]

Innodb row size limitation

I recently worked on a customer case where at seemingly random times, inserts would fail with Innodb error 139. This is a rather simple problem, but due to it’s nature, it may only affect you after you already have a system running in production for a while.

Optimizing slow web pages with mk-query-digest

I don’t use many tools in my consulting practice but for the ones I do, I try to know them as best as I can. I’ve been using mk-query-digest for almost as long as it exists but it continues to surprise me in ways I couldn’t imagine it would. This time I’d like to share […]

Where does HandlerSocket really save you time?

HandlerSocket has really generated a lot of interest because of the dual promises of ease-of-use and blazing-fast performance. The performance comes from eliminating CPU consumption. Akira Higuchi’s HandlerSocket presentation from a couple of months back had some really good profile results for libmysql versus libhsclient (starting at slide 15). Somebody in the audience at Percona […]

Lost innodb tables, xfs and binary grep

Before I start a story about the data recovery case I worked on yesterday, here’s a quick tip – having a database backup does not mean you can restore from it. Always verify your backup can be used to restore the database! If not automatically, do this manually, at least once a month. No, seriously […]

JOIN Performance & Charsets

We have written before about the importance of using numeric types as keys, but maybe you’ve inherited a schema that you can’t change or have chosen string types as keys for a specific reason. Either way, the character sets used on joined columns can have a significant impact on the performance of your queries. Take […]

Be careful when joining on CONCAT

The other day I had a case with an awful performance of a rather simple join. It was a join on tb1.vid = CONCAT(‘prefix-‘, tb2.id) with tb1.vid – indexed varchar(100) and tb2.id – int(11) column. No matter what I did – forced it to use key, forced a different join order, it did not want […]

Sphinx: Going Beyond full text search

I’ve already wrote a few times about various projects using Sphinx with MySQL for scalable Full Text Search applications. For example on BoardReader we’re using this combination to build search against over 1 billion of forum posts totaling over 1.5TB of data handling hundreds of thousands of search queries per day. The count of forum […]

Using CHAR keys for joins, how much is the overhead ?

I prefer to use Integers for joins whenever possible and today I worked with client which used character keys, in my opinion without a big need. I told them this is suboptimal but was challenged with rightful question about the difference. I did not know so I decided to benchmark. The results below are for […]

Why Index could refuse to work ?

Have you ever seen index which refused to be used even if there is every reason for it to work (from the glance view):

Why on the earth index would not be used you would think, even if MySQL is mentioning it in “possible keys” ? Should you try to force it ?