In MySQL 8.0 there are two new features designed to support lock handling: NOWAIT and SKIP LOCKED. In this post, we’ll look at how MySQL 8.0 handles hot rows. Up until now, how have you handled locks that are part of an active transaction or are hot rows? It’s likely that you have the application attempt to access the data, and if there is a lock on the requested rows, you incur a timeout and have to retry the transaction. These two new features help you to implement sophisticated lock handling scenarios allowing you to handle timeouts better and improve the application’s performance.

To demonstrate I’ll use this product table.

mysql> select @@version;
+-----------+
| @@version |
+-----------+
| 8.0.11    |
+-----------+
1 row in set (0.00 sec)

CREATE TABLE `product` (
`p_id` int(11) NOT NULL AUTO_INCREMENT,
`p_name` varchar(255) DEFAULT NULL,
`p_cost` decimal(19,4) NOT NULL,
`p_availability` enum('YES','NO') …

I was fortunate to attend an Ops discussion about databases at the OpenStack Summit Atlanta this past May as one of the panelists. The discussion was about deadlock issues OpenStack operators see with Percona XtraDB Cluster (of course this is applicable to any Galera-based solution). I asked to describe what they are seeing, and as it turned out, nova and neutron uses the SELECT … FOR UPDATE SQL construct quite heavily. This is a topic I thought was worth writing about.

Write set replication in a nutshell (with oversimplification)

Any node is writable, and replication happens in write sets. A write …