We all know disk based temporary tables are bad and you should try to have implicit temporary tables created in memory where possible, do to the fact that you should increase tmp_table_size to appropriate value and avoid using blob/text columns which force table creation on the disk because MEMORY storage engine does not support […]Read more
As you might know while running GROUP BY and some other kinds of queries MySQL needs to create temporary tables, which can be created in memory, using MEMORY storage engine or can be created on disk as MYISAM tables. Which one will be used depends on the allowed tmp_table_size and also by […]Read more
In this blog post, I’ll examine when looking at raw MySQL query logs can be more useful than working with tools that only have summary data.
In my previous blog post, I wrote about analyzing MySQL Slow Query Logs with ClickHouse and ClickTail. One of the follow-up questions I got is when do you […]
The MariaDB subquery cache feature added in MariaDB 5.3 is not widely known. Let’s see what it is and how it works.
What is a subquery cache?
The MariaDB subquery cache optimizes the execution of correlated subqueries. Correlated subqueries refer to a value from the parent query. For example:
SELECT id FROM product WHERE price NOT IN (SELECT […]Read more
Being a QA Engineer, how would you feel if you had access to a framework which can generate 80+ crashes – a mix of hitting developer introduced assertions (situations that should not happen), and serious unforeseen binary crashes – for the world’s most popular open source database software – each and ever hour? What if you […]Read more
I was fortunate to attend an Ops discussion about databases at the OpenStack Summit Atlanta this past May as one of the panelists. The discussion was about deadlock issues OpenStack operators see with Percona XtraDB Cluster (of course this is applicable to any Galera-based solution). I asked to describe what they are seeing, and […]Read more
A couple of weeks ago, shortly after Vadim wrote about Percona Cloud Tools and using Slow Query Log to capture the data, Mark Leith asked why don’t we just use Performance Schema instead? This is an interesting question and I think it deserves its own blog post to talk about.
First, I would say main […]
There are many blog posts already written on topics related to “MySQL server memory usage,” but nevertheless there are some who still get confused when troubleshooting issues associated with memory usage for MySQL. As a So it seems we have to understand the purpose for configuring any variable… either it is Global or Session […]Read more
We have always received quite a few questions here at Percona Support on how to avoid the dreaded “Too many connections” error, as well as what is the recommended value for max_connections. So, in this article, I will try to cover the best possible answers to these questions so others can mitigate similar kinds […]Read more
This is the second part in a two-part series comparing Virident’s vCache to FlashCache. The first part was focused on usability and feature comparison; in this post, we’ll look at some sysbench test results.
Disclosure: The research and testing conducted for this post were sponsored by Virident.
First, some background information. All tests were conducted on […]