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 MAX(price) FROM product GROUP BY category);

MariaDB only uses this optimization if the parent query is a SELECT, not an UPDATE or a DELETE. The subquery results get cached only for the duration of the parent query.

MariaDB added the subquery cache in v5.3. It is controlled by …

In this blog post, I’ll look for the bottleneck that prevented the performance in my previous post from achieving better results.

The powerful machine I used in the tests in my previous post has a comparatively slow disk, and therefore I expected my tests would hit a point when I couldn’t increase performance further due to the disk speed.

Hardware configuration:

Processors: physical = 4, cores = 72, virtual = 144, hyperthreading = yes
Memory: 3.0T
Disk speed: about 3K …

This procedure can be used to expand an LVM  database volume on Amazon AWS (but also apply to any storage area network environment equally). Let me start with this assumption: when you create volumes for database use in AWS using EBS, you stripe data across them in order to enhance performance.  If you aren't doing this... well, you should :-) Under this assumption, when you need to add more disk space to an existing database volume, you can't just add the disk(s) to the volume, as this would make the added space non striped, and would eventually create hotspots in the dataset. The correct approach in this situation is to create a number of new EBS disks enough to contain entire dataset plus the desired added space,so that you can grow the existing dataset while re-striping properly.
To make this clear, let's suppose you have a dataset volume of  3 TB,  made of 3 1TB EBS volumes which are striped across, but space is running …

In this blog post, we’ll look at Performance Schema benchmarks for OLTP Read/Write workloads.

I am in love with Performance Schema and talk a lot about it. Performance Schema is a revolutionary MySQL troubleshooting instrument, but earlier versions had performance issues. Many of these issues are fixed now, and the default options work quickly and …

Please join Laurynas Biveinis, Percona’s Technical Director – Engineering, on January 25, 2017, at 7 am EST (UTC-8) as he discusses “Percona Server for MySQL 5.7: Key Performance Algorithms.”

In this webinar, Laurynas will discuss selected areas of InnoDB and Percona Server for MySQL 5.7 internals as they relate to buffer pool management and flushing (from a performance and scalability point of view). He will describe the motivation behind the buffer pool mutex split, multi-threaded LRU flusher and parallel doublewrite features in Percona Server for MySQL 5.7, given that MySQL InnoDB 5.7 has re-implemented many of the same features found in Percona Server for MySQL – especially …

In this blog, I’ll look at the impact of swapping on MySQL performance. 

It’s common sense that when you’re running MySQL (or really any other DBMS) you don’t want to see any I/O in your swap space. Scaling the cache size (using

innodb_buffer_pool_size

 in MySQL’s case) is standard practice to make sure there is enough free memory so swapping isn’t needed.   

But what if you make some mistake or miscalculation, and swapping happens? How much does it really impact performance? This is exactly what I set out to investigate.

My test system has the following:

• 32GB of physical memory
• OS (and swap space) on a (pretty old) Intel 520 SSD device
• Database stored on Intel 750 NVMe storage

To simulate a worst case scenario, I’m using Uniform Sysbench Workload:

sysbench …

This blog compares how PostgreSQL and MySQL handle millions of queries per second.

Anastasia: Can open source databases cope with millions of queries per second? Many open source advocates would answer “yes.” However, assertions aren’t enough for well-grounded proof. That’s why in this blog post, we share the benchmark testing results from Alexander Korotkov (CEO of Development, Postgres Professional) and Sveta Smirnova (Principal Technical Services Engineer, Percona). The comparative research of PostgreSQL 9.6 and MySQL 5.7 performance will be especially valuable for environments with multiple databases.

The idea behind this research is to provide an honest comparison for the two popular RDBMSs. Sveta and Alexander wanted to test the most recent versions of both MySQL and PostgreSQL with the same tool, under the same challenging …

Why do we sometimes want to keep duplicate indexes?

I’ve done dutiful DBA work in the past to identify and remove what are commonly called duplicate indexes. That is, those indexes that look like (a) and (a,b). The thought is that a query will utilize an index as easily on (a) as on (a,b), and removing (a) will save storage cost and write performance. I’ve had the experience, though, of removing (a) and seeing performance tank.

(As an aside, these are really redundant indexes. A duplicate index would be (a,b) and (a,b) by two different names – this can commonly be done by object relational mapping (ORM) or other automated schema creation tools. I’ll call (a) and (a,b) redundant indexes below.)

This test is on Percona Server 5.7.14 with the sys schema installed and performance schema enabled.

Given two tables with the same number of rows and …

Great news: Group Replication is now officially released with MySQL 5.7.17, congratulations to everybody that worked so hard for it!

In this post I plan to share more details about the performance of Group Replication while addressing one of our frequently asked questions, which is how it performs compared to Galera.…

I’ve been lately compiling and generating .deb packages for several MySQL and MariaDB recent versions, and I wanted to try them more in depth -specially MySQL 8.0 and MariaDB 10.2, both of which are still in development.

Several people have already given their first impressions (or will do soon), and testing early is the best way to catch bugs and regressions, and get them fixed before the official release. In fact, as I will comment later, I ran into breaking bugs on both MySQL 8.0 and MariaDB 10.2, which I …