Section 6: "Profile a real case" 6.1 INTRODUCTION
Profiling & Debugging is an argument that would require an entire book, the aim of this(and the others) posts of this series is to give you the basic knowledge on how to work with these tools and techniques withing Eclipse. For instance if you want to learn to profile with OProfile you should study on the abundant and separate resources, you may start from: http://OProfile.sourceforge.net
6.2 ABOUT NAMING THE PROJECT
Today we had an interesting situation where the same query was executed significantly slower when it was written with GROUP BY instead of DISTINCT and I saw many people still had the assumption that these two types of queries are actually equivalent which is simply not true. Although DISTINCT queries can be implemented using GROUP BY but not every GROUP BY query can be translated to DISTINCT. Depending on the brand and the optimizer the database server may actually use group by internally for the execution of distinct but that won’t make them equivalent. Let’s see why…
GROUP BY as the name suggest groups the result by some set of parameters and evaluate the whole result set. In most databases group by is implemented based on sorting and the same rules applies to it as well.
DISTINCT will make sure that the same row won’t be returned in the result set twice. Distinct doesn’t necessary …
[Read more]For some time now I've been working on a Drupal site that consists mainly of scraped content from a proprietary, ASP based CMS from the late nineties. The Simple HTML Dom Parser, used from within a drush script, has been invaluable. It made scraping the old site content and importing it as Drupal nodes a relative breeze. (No access to the database used by the CMS, boo!)
Part of setting up the new site is importing users and their content profile nodes from a different Drupal site, that was setup a year or two ago to manage an event.
I had hoped there would be a way for me to export these users and their profile nodes from one Drupal to the other, but though I found modules to export one or the other, I might still end up with profile nodes that were no longer related to their users. Of course, that's pretty useless.
When I remembered I was also supposed …
[Read more]The “sla” in mysqlsla stands for “statement log analyzer”. This does a much better job than mysqldumpslow of analyzing your slow query log. In fact, you can sort by many different parameters — by sheer number of times the query shows up in the slow query log, by the total or average query [...]
Today I’ve been checking out a new client environment. My mission is to figure out (cold) some of the characteristics of the queries being run, and particularly if they’re “good” or “bad”. In my arsenal of “tools I really want to check out” has been Ma’atkit’s Query Profiler. They’re very different tools. Ma’atkit’s query [...]