April 19, 2014

A workaround for the performance problems of TEMPTABLE views

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 […]

Joining on range? Wrong!

The problem I am going to describe is likely to be around since the very beginning of MySQL, however unless you carefully analyse and profile your queries, it might easily go unnoticed. I used it as one of the examples in our talk given at phpDay.it conference last week to demonstrate some pitfalls one may […]

When the subselect runs faster

A few weeks ago, we had a query optimization request from one of our customer. The query was very simple like:

This column in the table is looks like this:

The table have 549252 rows and of course, there is an index on the col1. MySQL estimated the cardinality of that index as […]

Getting around optimizer limitations with an IN() list

There was a discussion on LinkedIn one month ago that caught my eye: Database search by “within x number of miles” radius? Anyone out there created a zipcode database and created a “search within x numer of miles” function ? Thankful for any tips you can throw my way.. J A few people commented that […]

Quick comparison of MyISAM, Infobright, and MonetDB

Recently I was doing a little work for a client who has MyISAM tables with many columns (the same one Peter wrote about recently). The client’s performance is suffering in part because of the number of columns, which is over 200. The queries are generally pretty simple (sums of columns), but they’re ad-hoc (can access […]

Guidance for MySQL Optimizer Developers

I spend large portion of my life working on MySQL Performance Optimization and so MySQL Optimizer is quite important to me. For probably last 10 years I chased first Monty and later Igor with Optimizer complains and suggestions. Here are some general ideas which I think can help to make optimizer in MySQL, MariaDB or […]

Multi Column indexes vs Index Merge

The mistake I commonly see among MySQL users is how indexes are created. Quite commonly people just index individual columns as they are referenced in where clause thinking this is the optimal indexing strategy. For example if I would have something like AGE=18 AND STATE=’CA’ they would create 2 separate indexes on AGE and STATE […]

A micro-benchmark of stored routines in MySQL

Ever wondered how fast stored routines are in MySQL? I just ran a quick micro-benchmark to compare the speed of a stored function against a “roughly equivalent” subquery. The idea — and there may be shortcomings that are poisoning the results here, your comments welcome — is to see how fast the SQL procedure code […]

What does Using filesort mean in MySQL?

If you were interviewing to work at Percona, and I asked you “what does Using filesort mean in EXPLAIN,” what would you say? I have asked this question in a bunch of interviews so far, with smart people, and not one person has gotten it right. So I consider it to be a bad interview […]

Optimizing repeated subexpressions in MySQL

How smart is the MySQL optimizer? If it sees an expression repeated many times, does it realize they’re all the same and not calculate the result for each of them? I had a specific case where I needed to find out for sure, so I made a little benchmark. The query looks something like this: