The latest from the MySQL community

Using the framework for testing we created in earlier articles, let’s try to modify some data. We are writing a small program that increments a counter. Our table looks like this, and contains 10 counters:

CREATE TABLE `demo` (
  `id` bigint unsigned NOT NULL AUTO_INCREMENT,
  `counter` int NOT NULL DEFAULT '0',
  UNIQUE KEY `id` (`id`)
)
INSERT INTO `demo` VALUES (1,0);
INSERT INTO `demo` VALUES (2,0);
...
INSERT INTO `demo` VALUES (10,0);

We are using some very simple programming to increment a counter:

@sql.command()
@click.option("--name", default="demo", help="Table name to count in")
@click.option("--id", default=0, help="Counter to use")
@click.option("--count", default=1000, help="Number of increments")
def count(name, id, count):
    """ Increment counter --id by --count many steps in table --name """
    for i in range(0, count):
        cmd = f"update {name} set counter=counter+1 where id = {id}"

        c = …

I wanted to be brave and I installed MySQL Group Replication manually…. it was painful !

Then I realized that managing those servers and especially deal with MySQL Routers was even more painful !

What are my options now ? Is there a solution or do I need to restart from scratch ?

Asking the answer is already answering it… and once again MySQL Shell at the rescue.

MySQL Group Replication

I’ve configured everything manually. I also loaded group_replication and clone plugins and finally after having bootstrapped my Group here is what I have:

mysql> select member_host, member_port port, member_state state, 
       member_role role, member_version version 
       from performance_schema.replication_group_members;
+-------------+------+--------+-----------+---------+
| member_host | port | state  | role      | version | …

After having a look how MySQL handles transactions physically, let’s have a look at what is going on from a logical point of view.

We are using a test table called demo with an id and a counter field, both integer. In it we have 10 counters, all set to 0.

CREATE TABLE `demo` (
  `id` bigint unsigned NOT NULL AUTO_INCREMENT,
  `counter` int NOT NULL DEFAULT '0',
  UNIQUE KEY `id` (`id`)
)
INSERT INTO `demo` VALUES (1,0);
INSERT INTO `demo` VALUES (2,0);
...
INSERT INTO `demo` VALUES (10,0);

In one session, we start a transaction and modify a counter value. We do not commit anything.

Session1> start transaction read write;
Session1> update demo set counter = 10 where id = 3;

Isolation

In a second session, we check the data and notice a few things:

Session2> select …

Introduction In this article, we are going to see how we can implement an audit logging mechanism using MySQL database triggers to store the old and new row states in JSON column types. Database tables Let’s assume we have a library application that has the following two tables: The book table stores all the books that are found in our library, and the book_audit_log table stores the CDC (Change Data Capture) events that happened to a given book record via an INSERT, UPDATE, or DELETE DML statement. The book_audit_log table is created... Read More

The post MySQL audit logging using triggers appeared first on Vlad Mihalcea.

I got this question on the “How to Avoid Pitfalls in Schema Upgrade with Percona XtraDB Cluster (PXC)” webinar and wanted to answer it in a separate post.

Will RSU have an effect on GTID consistency if replication PXC cluster to another cluster?

Answer for this: yes and no.

Galera assigns its own GTID for the operations, replicated to all nodes of the cluster. Such operations include DML (

INSERT/UPDATE/DELETE

 ) on InnoDB tables and DDL commands, executed with default TOI method. You can find more details on how GTIDs work in the Percona XtraDB Cluster in this blog post.

However, DDL commands, executed with RSU method, are …

I would say that innodb_rollback_on_timeout is a very important parameter. In this blog, I am going to explain “innodb_rollback_on_timeout” and how it affects the transaction behavior at the MySQL level. I describe two scenarios with practical tests, as it would be helpful to understand this parameter better.

What is innodb_rollback_on_timeout?

The parameter Innodb_rollback_on_timeout will control the behavior of the transaction when a failure occurs with timeout.

• If –innodb-rollback-on-timeout=OFF ( default ) is specified, InnoDB rollbacks only the last statement on a transaction timeout.
• If –innodb-rollback-on-timeout=ON is specified, a transaction timeout causes InnoDB to abort and roll back the entire transaction.

Let’s conduct the test with the …

When writing data to disk, for small transactions the cost of writing the commit out do disk dominates the execution time of the script. In order to show that, I wrote a little bit of Python.

The script creates a test table in a database and writes 10.000 rows of test data into it, in commit sizes of 1, 2, 4, …, 1024 rows.

$ ./mysql.py --help
Usage: mysql.py [OPTIONS] COMMAND [ARGS]...

  Test commit sizes.

Options:
  --help  Show this message and exit.

Commands:
  create    Create the demo table empty.
  drop      Drop the demo table
  fill      Write test records into the demo table.
  truncate  Truncate the demo table.

There is a small driver script to run the test. The driver creates the table, truncates it and will then run the fill command of the script over and over again, with growing commit-sizes. All powers of 2 from 0 to 10 are being tried with 10.000 rows of test data.

The test system has a …

So you talk to a database, doing transactions. What happens actually, behind the scenes? Let’s have a look.

There is a test table and we write data into it inside a transaction:

CREATE TABLE t (
  id serial,
  data varbinary(255)
)

START TRANSACTION READ WRITE
INSERT INTO t ( id, data ) VALUES (NULL, RANDOM_BYTES(255))
COMMIT

The MySQL test instance we are talking to is running on a Linux machine, and otherwise idle to make observation easier. Also, we configured it with innodb_use_native_aio = false because observing actual physical asynchronous I/O and attributing it to the statement that caused it is really hard.

Setting things up this way, we can use lsof and strace to see things. But before we do this, let’s set some expectations and establish some background knowledge.

The Log/Data Memory/Storage quadrants

Upper half: Log structures, Lower half: Data …

On July 21, 2020, Percona delivered an updated version of our Percona Kubernetes Operator for Percona XtraDB Cluster (PXC) focused on easing deployment and operations management of a clustered MySQL environment. Included in the Percona Distribution for MySQL, our Operator is based on the best practices for MySQL cluster configuration and setup in Kubernetes. This update adds a variety of important new features including:

Smart Update to Safely and Reliably Upgrade your PXC Environment Automatically
We implemented a new update strategy called Smart Update. Smart Update is aware of the context of your environment and minimizes the number of failover events that need to occur to fully upgrade a …

Dear MySQL users,

MySQL Shell 8.0.21 is a maintenance release of MySQL Shell 8.0 Series (a
component of the MySQL Server). The MySQL Shell is provided under
Oracle’s dual-license.

MySQL Shell 8.0 is highly recommended for use with MySQL Server 8.0 and
5.7. Please upgrade to MySQL Shell 8.0.21.

MySQL Shell is an interactive JavaScript, Python and SQL console
interface, supporting development and administration for the MySQL
Server. It provides APIs implemented in JavaScript and Python that
enable you to work with MySQL InnoDB cluster and use MySQL as a document
store.

The AdminAPI enables you to work with MySQL InnoDB cluster and InnoDB
ReplicaSet, providing integrated solutions for high availability and scalability
using InnoDB based MySQL databases, without requiring advanced MySQL
expertise.  For more …