This is part two in my six part series on business intelligence, with a focus on OLAP analysis. Part 1 – Intro to OLAP Identifying the differences between a data warehouse and a data mart. (this post) Introduction to MDX and the kind of SQL which a ROLAP tool must generate to answer those queries. [...]
Intro to OLAP
July 12, 2010 By 10 Comments
This is the first of a series of posts about business intelligence tools, particularly OLAP (or online analytical processing) tools using MySQL and other free open source software. OLAP tools are a part of the larger topic of business intelligence, a topic that has not had a lot of coverage on MPB. Because of this, [...]
EXPLAIN EXTENDED can tell you all kinds of interesting things
June 15, 2010 By 7 Comments
While many people are familiar with the MySQL EXPLAIN command, fewer people are familiar with “extended explain” which was added in MySQL 4.1 EXPLAIN EXTENDED can show you what the MySQL optimizer does to your query. You might not know this, but MySQL can dramatically change your query before it actually executes it. This process [...]
Percona Welcomes Justin Swanhart
May 26, 2010 By 2 Comments
Percona is pleased to officially welcome Justin Swanhart to our team of consultants. Before joining Percona, Justin worked as a MySQL DBA at Gazillion, Yahoo, and Kickfire. Justin has become a regular contributor here on the MySQL Performance Blog as well as being an active blogger at http://swanhart.livejournal.com/. He is very active in the community, [...]
Beyond great cache hit ratio
May 19, 2010 By 2 Comments
I worked with application recently which has great memcached hit ratio – over 99% but yet still has average page response time over 500ms. Reason ? There are hundreds memcached gets and even though they have some 0.4ms response time they add up to add hundreds of ms to the total response time.
A workaround for the performance problems of TEMPTABLE views
May 19, 2010 By 7 Comments
MySQL supports two different algorithms for views: the MERGE algorithm and the TEMPTABLE algorithm. These two algorithms differ greatly. A view which uses the MERGE algorithm can merge filter conditions into the view query itself. This has significant performance advantages over TEMPTABLE views. A view which uses the TEMPTABLE algorithm will have to compute the [...]
Interviews for InfiniDB and TokuDB are next
November 16, 2009 By Leave a Comment
I forwarded on a list of questions about PBXT to Paul McCullagh today. While Paul’s busy answering them, I’d like to announce that Robert Dempsey (InfiniDB storage engine) and Bradley C. Kuszmaul (TokuDB storage engine) have also accepted an interview. If you have any questions about either storage engine, please post them here by Friday [...]
Just do the math!
July 6, 2009 By 4 Comments
One of the most typical reasons for performance and scalability problems I encounter is simply failing to do the math. And these are typically bad one because it often leads to implementing architectures which are not up for job they are intended to solve. Let me start with example to make it clear. Lets say [...]
How much memory can MySQL use in the worst case?
February 12, 2009 By 17 Comments
I vaguely recall a couple of blog posts recently asking something like “what’s the formula to compute mysqld’s worst-case maximum memory usage?” Various formulas are in wide use, but none of them is fully correct. Here’s why: you can’t write an equation for it.
Computing 95 percentile in MySQL
November 28, 2008 By 5 Comments
When doing performance analyzes you often would want to see 95 percentile, 99 percentile and similar values. The “average” is the evil of performance optimization and often as helpful as “average patient temperature in the hospital”. Lets set you have 10000 page views or queries and have average response time of 1 second. What does [...]
