In my previous blog post, I explained the internals of the sorted index build process. The blog ended with saying “there is one disadvantage.”

Beginning in MySQL 5.6, many DDLs including ALTER TABLE ADD INDEX became “ONLINE”. Meaning, when the ALTER is in progress, there can be concurrent SELECTS and DMLs. See the MySQL documentation for online DDL. From the documentation, we can see that ALTER TABLE ADD INDEX DDL permits concurrent DML.

The main disadvantage with Sorted Index Builds introduced in 5.7 is the reduced insert performance when ALTER is in progress. In this blog, we specifically talk about single thread insert performance on a table with ALTER ADD INDEX in progress.

If the table …

Percona is glad to announce the release of Percona XtraDB Cluster 5.7.26-31.37 on June 26, 2019. Binaries are available from the downloads section or from our software repositories.

Percona XtraDB Cluster 5.7.26-31.37 is now the current release, based on the following:

• Percona Server for MySQL 5.7.26-29
• Codership WSREP API release 5.7.25
• Codership Galera library 3.26

All Percona software is open-source and free.

Bugs Fixed

• PXC-2480: In some …

The Question Recently, a customer asked us:

What would cause a node switch to fail in a Tungsten Cluster?

For example, we saw the following during a recent session where a switch failed:

cctrl> switch to db3 

SELECTED SLAVE: db3@alpha 
SET POLICY: MAINTENANCE => MAINTENANCE 
PURGE REMAINING ACTIVE SESSIONS ON CURRENT MASTER 'db1@alpha' 
PURGED A TOTAL OF 0 ACTIVE SESSIONS ON MASTER 'db1@alpha' 
FLUSH TRANSACTIONS ON CURRENT MASTER 'db1@alpha' 
Exception encountered during SWITCH. 
Failed while setting the replicator 'db1' role to 'slave' 
ClusterManagerException: Exception while executing command 'replicatorStatus' on manager 'db1' 
Exception=Failed to execute '/alpha/db1/manager/ClusterManagementHelper/replicatorStatus alpha db3' 
Reason= 
CLUSTER_MEMBER(true) 
STATUS(FAIL) 
+----------------------------------------------------------------------------+ 
|alpha | …

In this blog post, I am going to show why we have to be careful with stored functions in select list, as a single query can cause thousands of queries in the background if we aren’t cautious.

For this example, I am only going to use the SLEEP function to demonstrate the issue, but you could use any other stored functions.

Here is the test schema and data:

DROP TABLE IF EXISTS t1;
CREATE TABLE t1 (
 id INT NOT NULL PRIMARY KEY auto_increment,
 gcol INT NOT NULL,
 fcol INT NOT NULL,
 INDEX (gcol)
);
INSERT INTO t1 VALUES (NULL,1,1),(NULL,2,1),(NULL,3,1),(NULL,4,2),(NULL,5,1);

And the first query:

mysql [localhost] {msandbox} (test) > SELECT gcol, SLEEP(1) FROM t1 WHERE 1 GROUP BY gcol LIMIT 1;
+------+----------+
| gcol | SLEEP(1) |
+------+----------+
|    1 |        0 |
+------+----------+
1 row in set (1.00 sec)

The query takes one second, which means the …

Recently I had a case where queries against Aurora Reader were 2-3 times slower than on the Writer node. In this blog post, we are going to discuss why.

I am not going to go into the details of how Aurora works, as there are other blog posts discussing that. Here I am only going to focus on one part.

The Problem

My customer reported there is a huge performance difference between the Reader and the Writer node just by running selects. I was a bit surprised, as the select queries should run locally on the reader node, the dataset could fit easily in memory, there were no reads on disk level, and everything looked fine.

I was trying to rule out every option when one of my colleagues mentioned I should have a look at the InnoDB_Adaptive_Hash_Indexes. He was right – it …

I am currently running tests with sysbench and dbdeployer on a Google Cloud Platform Debian 9 instance.  I ran into an interesting limit and lifting it was not straightforward.  I hope that by sharing this, you can avoid losing too much time.

The benchmark I am using is the insert benchmark.  I am able to run it with 2048 threads but I am not able to run it with 4096 threads (and yes, it makes

Welcome back to our blog series, Benefits of SQL Diagnostic Manager for MySQL (formerly Monyog). Last week, we discussed some of the challenges associated with MySQL and MariaDB database systems. Today, we dive in to additional features of SQL Diagnostic Manager for MySQL, including agentless monitoring technology, cloud readiness, and customization options.

Agentless Monitoring

Unlike other monitoring and advisory tools for MySQL and MariaDB, SQL Diagnostic Manager for MySQL does not require installing monitoring agents on each MySQL and MariaDB server. Installing and maintaining monitoring agents can be a complex administration task by itself.

SQL Diagnostic Manager for MySQL uses a standard MySQL connection for monitoring. To collect data for the operating system from remote database servers, …

I receive many questions about errors being reported about pt-kill… and often those errors are not real. The main problem I have found is that pt-kill is hard to understand and the documentation doesn’t have many examples (I’ll add them), so, I decided to write a post about the most common usage of pt-kill: to kill the queries that match a regexp (usually a SELECT) and have been running for more than n seconds.

Let’s assume that we are running a tool like sysbench that executes queries like:

select distinct c from sbtest1 where id between 1 and 20 order by c
select distinct c from sbtest2 where id between 5 and 25 order by c
select distinct c from sbtest3 where id between 3 and 7 order by c
select distinct c from sbtest1 where id between 2 and 8 order by c
select distinct c from sbtest3 where id between 15 and 30 order by c

and at the same time, in a different process, we are running:

SELECT SLEEP …

Overview The Skinny

In this blog post we will define what a split-brain scenario means in a MySQL database cluster, and then explore how a Tungsten MySQL database cluster reacts to a split-brain situation.

Agenda What’s Here?

• Define the term “split-brain”
• Briefly explore how the Tungsten Manager works to monitor the cluster health and prevent data corruption in the event of a network partition
• Also explore how the Tungsten Connector works to route writes
• Describe how a Tungsten MySQL database cluster reacts to a split-brain situation
• Illustrate various testing and recovery procedures

Split-Brain: Definition and Impact Sounds scary, and it is!

A split-brain occurs when a MySQL database cluster which normally has …

We would like to remind you about the shows where you can find MySQL during next week, Jun 24-Jun30. Please find them below.

• Devoxx, Krakow, Poland, Jun 24-26, 2019

  • You can find MySQL among other groups (Java, Graal VM, Fn, Linux) at the Oracle booth in the expo area. Do not miss the demos (not only MySQL) we are going to run at our booth.
• MySQL User Group Frankfurt - MySQL Meetup, Germany, Jun 27, 2019
  • We are happy to invite you to join the MySQL meetup organized by MySQL User Group Frankfurt. This time Carsten Thalheimer, the  MySQL Master Principal Sales consultant is invited as a speaker. He will be talking about "MySQL 8 - The Next big Thing". The meetup starts at 7pm. More …