Thanks for all, who attended my webinar, I got many questions and I wanted to take this opportunity to answer them. Q: Even ntp has a delay of 0.3-0.4 between servers does that mean a 0.25 as from logs can be an issue ? A: My demo vms were running for a few hours before [...]
Replaying database load with Percona Playback
October 25, 2012 By 9 Comments
If you are planning to upgrade or make any configuration change on your MySQL database the first advice usually is: – Benchmark! How should we do that benchmark? People usually run generic benchmark tools like sysbench, tpcc or mysqlslap that are good to know the number of transactions per seconds that a database can do [...]
The Math of Automated Failover
September 18, 2012 By 9 Comments
There are number of people recently blogging about MySQL automated failover, based on production incident which GitHub disclosed. Here is my take on it. When we look at systems providing high availability we can identify 2 cases of system breaking down. First is when the system itself has a bug or limitations which does not [...]
How to find MySQL queries worth optimizing ?
September 11, 2012 By 6 Comments
One question I often get is how one can find out queries which should be optimized. By looking at pt-query-digest report it is easy to find slow queries or queries which cause the large portion of the load on the system but how do we know whenever there is any possibility to make this query [...]
Differences between READ-COMMITTED and REPEATABLE-READ transaction isolation levels
August 28, 2012 By 3 Comments
As an instructor with Percona I’m sometimes asked about the differences between the READ COMMITTED and REPEATABLE READ transaction isolation levels. There are a few differences between READ-COMMITTED and REPEATABLE-READ, and they are all related to locking.
Hidden columns of query_review_history table
August 28, 2012 By Leave a Comment
You can use pt-query-digest to process a MySQL slow query log and store historical values for review trend analysis into query_review_history table. According to its official documentation you can populate many columns in that table but there are other important ones such as ‘user’, ‘host’, ‘db’ which are not included by default. I will explain [...]
Recovery deleted ibdata1
August 10, 2012 By 9 Comments
Recently I had a case when a customer deleted the InnoDB main table space – ibdata1 – and redo logs – ib_logfile*. MySQL keeps InnoDB files open all the time. The following recovery technique is based on this fact and it allowed to salvage the database. Actually, the files were deleted long time ago – [...]
MySQL Indexing: Best Practices Webinar
August 7, 2012 By 3 Comments
I’m hosting MySQL Indexes: Best Practices Webinar next week, Wednesday August 15. In which I will talk about how MySQL indexes are structured and how they can be used, as well as go over the best practices in selecting correct indexes for your database workloads. Indexing looks like a very basic topic, but it is [...]
Innodb Table Locks
July 31, 2012 By 4 Comments
Innodb uses row level locks right ? So if you see locked tables reported in SHOW ENGINE INNODB STATUS you might be confused and rightfully so as Innodb table locking is a bit more complicated than traditional MyISAM table locks. Let me start with some examples. First lets run SELECT Query:
1 2 3 4 5 | ---TRANSACTION 12303, ACTIVE 26 sec mysql tables in use 2, locked 0 MySQL thread id 53038, OS thread handle 0x7ff759b22700, query id 3918786 localhost root Sending data select count(*) from sbtest,sbtest x Trx read view will not see trx with id >= 12304, sees < 12301 |
As you can [...]
Percona XtraDB Cluster reference architecture with HaProxy
June 20, 2012 By 63 Comments
This post is a step-by-step guide to set up Percona XtraDB Cluster (PXC) in a virtualized test sandbox. I used Amazon EC2 micro instances, but the content here is applicable for any kind of virtualization technology (for example VirtualBox). The goal is to give step by step instructions, so the setup process is understandable and [...]
