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 …

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10:00 – 11:00am PDT     Customer Insights …

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 …

A new release of MySQL was out on July 13 (8.0.21).
Among all the changes, there are some that I have already tested and that I really appreciate.

Who stopped the MySQL server?

In previous releases, I can already see in the error log file who stopped the MySQL server if this was done through the shutdown statement.
In MySQL 8.0.20:

mysql> shutdown;
Query OK, 0 rows affected (0.00 sec)
mysql> exit;
Bye
# tail -2 /u01/app/mysql/admin/mysqld2/log/mysqld2.err
2020-07-23T20:39:08.049064+02:00 9 [System] [MY-013172] [Server] Received SHUTDOWN from user root. Shutting down mysqld (Version: 8.0.20).
2020-07-23T20:39:09.796726+02:00 0 [System] [MY-010910] [Server] /u01/app/mysql/product/mysql-8.0.20/bin/mysqld: Shutdown complete (mysqld 8.0.20)  MySQL Community Server - GPL.

In MySQL 8.0.21:

mysql> …

A new release of MySQL was out on July 13 (8.0.21).
Among all the changes, there are some that I have already tested and that I really appreciate.

Who stopped the MySQL server?

In previous releases, I can already see in the error log file who stopped the MySQL server if this was done through the shutdown statement.
In MySQL 8.0.20:

mysql> shutdown;
Query OK, 0 rows affected (0.00 sec)
mysql> exit;
Bye
# tail -2 /u01/app/mysql/admin/mysqld2/log/mysqld2.err
2020-07-23T20:39:08.049064+02:00 9 [System] [MY-013172] [Server] Received SHUTDOWN from user root. Shutting down mysqld (Version: 8.0.20).
2020-07-23T20:39:09.796726+02:00 0 [System] [MY-010910] [Server] /u01/app/mysql/product/mysql-8.0.20/bin/mysqld: Shutdown complete (mysqld 8.0.20)  MySQL Community Server - GPL.

In MySQL 8.0.21:

mysql> …

From MySQL 8.0.21 onwards, START GROUP_REPLICATION includes new options which allow a user to specify credentials to be used for distributed recovery. You can now pass credentials when invoking START GROUP_REPLICATION instead of setting them when configuring the group_replication_recovery channel.

START GROUP_REPLICATION command now has the options:

• USER: User name.

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This morning, a user asked in the MySQL Community Slack if somebody had an idea why the error log was filled up continuously with a warning messages like this one:

2020-07-24T06:54:00.877128Z 46 [Warning] [MY-013360] [Server] 
Plugin sha256_password reported: ''sha256_password' is deprecated and will be removed in 
a future release. Please use caching_sha2_password instead'

The context was that the user upgraded from MySQL 5.7 to MySQL 8.0 and changed the authentication plugin of all users to caching_sha2_password.

As the warning message was written to the error log almost twice per second, I suspected a monitoring tool. The user said, that no application, no monitoring was using this server yet.

Of course we verified that all users had the plugin changed.

This is important when helping people (friends, colleagues, …

Group Replication enables you to create fault-tolerant systems with redundancy by replicating the system state to a set of servers. Even if some of the servers subsequently fail, as long it is not all or a majority, the system is still available.…

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There may come a time you need to rename one or more columns in an existing MySQL table for a variety of reasons. Using ALTER TABLE, to rename a column is an easy enough command. But, suppose there are multiple tables in the same database/schema that have the same-named column and all of those columns need to be renamed. That could be a lot of ALTER TABLE statements to type out. Save your energy and time, avoiding all of those ALTER TABLE commands all-together. If you are lucky enough to be working with a MySQL version > 8.0 then the Shell is your salvation. With just a few lines of Python code in \py mode, all of your trouble(s) and headache(s) are no more…

Photo by Ibrahim Rifath on …

These are my notes for creating a small Node.js application that queries a MySQL database. The post will show you how to:

1. Configure your Node.js development directory.
2. Build a small application to test a MySQL connection.
3. Build a small application that connects to the MySQL database and queries data.

This blog post assumes you’ve performed a global install of Node.js on a Linux server. If you’re unfamiliar with how to perform a global Node.js installation, I cover how to do it in this earlier blog post.

Before you write the Node.js applicaiton, you need to setup a db developer directory. Then, create a node_modules symbolic link to the /usr/local/lib/node_modules directory in the db directory. You can use the following command …