I had a lot of questions on my MySQL Indexing: Best Practices Webinar (both recording and slides are available now) We had lots of questions. I did not have time to answer some and others are better answered in writing anyway. Q: One developer on our team wants to replace longish (25-30) indexed varchars with [...]
SQL Injection Questions Followup
July 26, 2012 By 2 Comments
I presented a webinar today about SQL Injection, to try to clear up some of the misconceptions that many other blogs and articles have about this security risk. You can register for the webinar even now that I’ve presented it, and you’ll be emailed a link to the recording, which will be available soon. During [...]
Percona XtraDB Cluster: Failure Scenarios with only 2 nodes
July 25, 2012 By 6 Comments
During the design period of a new cluster, it is always advised to have at least 3 nodes (this is the case with PXC but it’s also the same with PRM). But why and what are the risks ? The goal of having more than 2 nodes, in fact an odd number is recommended in [...]
On Character Sets and Disappearing Tables
June 21, 2012 By 1 Comment
The MySQL manual tells us that regardless of whether or not we use “SET FOREIGN_KEY_CHECKS=0″ before making schema changes, InnoDB will not allow a column referenced by a foreign key constraint to be modified in such a way that the foreign key will reference a column with a mismatched data type. For instance, if we [...]
pt-online-schema-change and default values
June 21, 2012 By 1 Comment
When I’m doing conventional ALTER TABLE in MySQL I can ignore default value and it will be assigned based on the column type. For example this alter table sbtest add column v varchar(100) not null would work even though we do not specify default value. MySQL will assign empty string as default default value for [...]
New distribution of random generator for sysbench – Zipf
May 9, 2012 By 3 Comments
Sysbench has three distribution for random numbers: uniform, special and gaussian. I mostly use uniform and special, and I feel that both do not fully reflect my needs when I run benchmarks. Uniform is stupidly simple: for a table with 1 mln rows, each row gets equal amount of hits. This barely reflects real system, [...]
InnoDB’s gap locks
March 27, 2012 By 15 Comments
One of the most important features of InnoDB is the row level locking. This feature provides better concurrency under heavy write load but needs additional precautions to avoid phantom reads and to get a consistent Statement based replication. To accomplish that, row level locking databases also acquire gap locks. What is a Phantom Read A [...]
How FLUSH TABLES WITH READ LOCK works with Innodb Tables
March 23, 2012 By 20 Comments
Many backup tools including Percona Xtrabackup, MyLVMBackup and others use FLUSH TABLES WITH READ LOCK to temporary make MySQL read only. In many cases the period for which server has to be made read only is very short, just few seconds, yet the impact of FLUSH TABLES WITH READ LOCK can be quite large because [...]
STOP: DELETE IGNORE on Tables with Foreign Keys Can Break Replication
February 2, 2012 By 1 Comment
DELETE IGNORE suppresses errors and downgrades them as warnings, if you are not aware how IGNORE behaves on tables with FOREIGN KEYs, you could be in for a surprise. Let’s take a table with data as example, column c1 on table t2 references column c1 on table t1 – both columns have identical set of rows for [...]
Percona testing: Quick test clusters with kewpie!
January 13, 2012 By Leave a Comment
The announcement of Percona XtraDB Cluster seems to have generated a fair bit of interest : ) Although the documentation contains more formal instructions for setting up a test cluster, I wanted to share a quick way to set up an ad-hoc cluster on a single machine to help people play with this (imho) rather [...]
