MySQL 8.0 Architecture and Enhancement Webinar: Q & A

In this blog, I will provide answers to the Q & A for the MySQL 8.0 Architecture and Enhancement webinar.

First, I want to thank everybody for attending my April 9, 2019, webinar. The recording and slides are available here. Below is the list of your questions that I was unable to answer fully during the webinar.

Q: What kind of Encryption levels are provided into MySQL 8.0?

The MySQL data-at-rest encryption feature supports the Advanced Encryption Standard (AES) block-based encryption algorithm.

In MySQL block_encryption_mode variable controls the block encryption mode. The default setting is aes-128-ecb. Set this option to aes-256-cbc, for example, under the [mysqld] option group in the MySQL configuration file (/etc/my.cnf):

[mysqld]
block_encryption_mode=aes-256-cbc

Q: At what frequency does the redo log buffer flush the changes to disk? When is the commit variable set to zero?

Here’s an overview:

• innodb_flush_log_at_trx_commit variable can be configured to set flush frequency in MySQL 5.7 and 8.0 it’s set to 1 by default.
• innodb_flush_log_at_trx_commit =0  logs are written and flushed to disk once per second. Transactions for which logs have not been flushed can be lost in a crash.
• innodb_flush_log_at_trx_commit =1 is required for full ACID compliance. Logs are written and flushed to disk at each transaction commit. Default Setting.
• innodb_flush_log_at_trx_commit =2 logs are written after each transaction commit and flushed to disk once per second. Transactions for which logs have not been flushed can be lost in a crash.

Q: How are persistent variables reset?

Using the RESET PERSIST command we can remove persisted global system variable settings from the mysqld-auto.cnf.

Example:

mysql > SET PERSIST binlog_encryption=ON;
Query OK, 0 rows affected (0.00 sec)
$ cat data/mysqld-auto.cnf
{ "Version" : 1 , "mysql_server" : { "mysql_server_static_options" : { "binlog_encryption" : { "Value" : "ON" , "Metadata" : { "Timestamp" : 1554896858076255 , "User" : "msandbox" , "Host" : "localhost" } } } } }
MySQL > RESET PERSIST binlog_encryption;
Query OK, 0 rows affected (0.00 sec)
$ cat data/mysqld-auto.cnf
{ "Version" : 1 , "mysql_server" : { } }

To reset all persistent variables use following command.

mysql > RESET PERSIST;
Query OK, 0 rows affected (0.00 sec)

Q: Does pt-config-diff work with these persistent vs. my.cnf variable settings?

No, it will not work. Due to config format differences in these files.

$ pt-config-diff ./my.sandbox.cnf data/mysqld-auto.cnf
Cannot auto-detect the MySQL config format at /home/lalit/perl5/bin/pt-config-diff line 3010.

Q: Regarding the UNDO Tablespace, do we have any specific retention to follow?

This is not required because in MySQL 8.0, the innodb_undo_log_truncate variable is enabled by default. It will perform an automatic truncate operation on the UNDO tablespace. When undo tablespaces exceed the threshold value defined by innodb_max_undo_log_size (default value is 1024 MiB) they are marked for truncation.

Truncating the undo tablespace performs the following action:

1. Performs deactivation of undo tablespace
2. Truncation of undo tablespace
3. Reactivation of undo tablespaces

NOTE:  Truncating undo logs that reside in the system tablespace is not supported. 

Q: Corrupted data on disk where the secondary indexes don’t match to the primary?

I’ll be happy to respond to this, but I’ll need a little bit more information… feel free to add more detail to the comments section and I’ll see if I can provide some insight.

Thanks for attending this webinar on MySQL 8.0 Architecture and Enhancement Webinar . You can find the slides and a recording here.