In my previous blog post, I talked about new general tablespaces in MySQL 8.0. Recently MySQL 8.0.3-rc was released, which includes a new data dictionary. My goal is to create one million tables in MySQL and test the performance.

Background questions

Q: Why million tables in MySQL? Is it even realistic? How does this happen?

Usually, millions of tables in MySQL is a result of “a schema per customer” Software as a Service (SaaS) approach. For the purposes of customer data isolation (security) and logical data partitioning (performance), each “customer” has a dedicated schema. You can think of a WordPress hosting service (or any CMS based hosting) where each …

In this blog post, we’ll look at how to avoid shared locks from subqueries.

I’m pretty sure most of you have seen an UPDATE statement matching rows returned from a SELECT query:

update ibreg set k=1 where id in (select id from ibcmp where id > 90000);

This query, when executed with

autocommit=1

, is normally harmless. However, this can have bad effects when combined with other statements in the same transaction that result in holding the shared locks from the SELECT query. But first, let me explain why the SELECT query would hold locks in the first place.

Due to InnoDB’s ACID properties, to make sure that the outer UPDATE statement has a consistent view of the matching rows from the SELECT query the server has to acquire a shared lock on those rows. No other thread should modify …

Welcome to the first day of the Percona Live Open Source Database Conference Europe 2017: Tutorials day! Technically the first day of the conference, this day focused on provided hands-on tutorials for people interested in learning directly how to use open source tools and technologies.

Today attendees went to training sessions taught by open source database experts and got first-hand experience configuring, working with, and experimenting with various open source technologies and software.

The first full day (which includes opening keynote speakers and breakout sessions) starts Tuesday 9/26 at 9:15 am.

Some of the tutorial topics covered today were:

…

For most people (including me until recently) database XA transactions are a fuzzy concept. In over eight years with Percona, I have never had to deal with XA transactions. Then a few weeks ago I got two customers having issues with XA transactions. That deserves a post.

XA 101

What are XA transactions? XA transactions are useful when you need to coordinate a transaction between different systems. The simplest example could be simply two storage engines within MySQL. Basically, it follows this sequence:

1. XA START
2. Some SQL statements
3. XA END
4. XA PREPARE
5. XA COMMIT or ROLLBACK

Once prepared, the XA transaction survives a MySQL crash. Upon restart, you’ll see something like this in the MySQL error log:

2017-08-23T14:53:54.189068Z 0 [Note] …

Join Percona Chief Evangelist Colin Charles as he covers happenings, gives pointers and provides musings on the open source database community.

Percona Live Europe Dublin

Are you affected by the Ryanair flight cancellations? Have you made alternative arrangements? Have you registered for the community dinner? Even speakers have to register, so this is a separate ticket cost! There will be fun lightning talks in addition to food and drink.

You are, of course, already registered for Percona Live Europe Dublin, …

In this blog post, I will demonstrate how to run and use sysbench histograms.

One of the features of sysbench that I often I see overlooked (and rarely used) is its ability to produce detailed query response time histograms in addition to computing percentile numbers. Looking at histograms together with throughput or latency over time provides many additional insights into query performance.

Here is how you get detailed sysbench histograms and performance over time:

sysbench --rand-type=uniform --report-interval=1 --percentile=99 --time=300 --histogram --mysql-password=sbtest oltp_point_select --table_size=400000000 run

There are a few command line options to consider:

• report-interval=1 – prints out the current performance measurements every second, which helps see if …

Welcome to another post in our series of interview blogs for the upcoming Percona Live Europe 2017 in Dublin. This series highlights a number of talks that will be at the conference and gives a short preview of what attendees can expect to learn from the presenter.

This blog post is with Dana Van Aken, a Ph.D. student in Computer Science at Carnegie Mellon University. Her talk is titled Automatic Database Management System Tuning Through Large-Scale Machine Learning. DBMSs are difficult to manage because they have hundreds of configuration “knobs” that control factors such as the amount of memory to use for …

Welcome to another post in our series of interview blogs for the upcoming Percona Live Europe 2017 in Dublin. This series highlights a number of talks that will be at the conference and gives a short preview of what attendees can expect to learn from the presenter.

This blog post is with Charity Majors, CEO/Cofounder of Honeycomb. Her talk is Debugging with Logs (and Other Events). Her presentation covers some of the lessons every engineer should know (and often learns the hard way): why good logging solutions are so expensive, why treating your logs as strings can be costly and dangerous, how logs can impact code …

In this blog, I’ll look at how to use ClickHouse for parallel log processing.

Percona is seen primarily for our expertise in MySQL and MongoDB (at this time), but neither is quite suitable to perform heavy analytical workloads. There is a need to analyze data sets, and a very popular task is crunching log files. Below I’ll show how ClickHouse can be used to efficiently perform this task. ClickHouse is attractive because it has multi-core parallel query processing, and it can even execute a single query using multiple CPUs in the background.

I am going to check how ClickHouse utilizes multiple CPU cores and threads. I will use a server with two sockets, equipped with “Intel(R) Xeon(R) CPU E5-2683 v3 @ 2.00GHz” in each. That gives a total of 28 CPU cores / 56 CPU threads.

To analyze workload, I’ll use an Apache log file from one of Percona’s servers. …

In this post, we will discuss how to search code with the help of cscope. Let’s begin by checking its description and capabilities (quoting directly from http://cscope.sourceforge.net/):

Cscope is a developer’s tool for browsing source code.

• Allows searching code for:
  • all references to a symbol
  • global definitions
  • functions called by a function
  • functions calling a function
  • text string
  • regular expression pattern
  • a file
  • files including a file
• Curses based (text screen)
• An …