When executing an ALTER TABLE, InnoDB (and XtraDB) will create two InnoDB transactions:
table_nametrx id XXXX lock mode S” in SHOW ENGINE INNODB STATUS.
A little known fact is that the InnoDB data dictionary is somewhat transactional (the big thing it’s missing is any form of MVCC. It’s not ACID). The largest part of ALTER TABLE not being completely crash safe in MySQL is the MySQL server manipulating FRM files.
The only MySQL storage engine I’m aware of having fully crash safe DDL is MySQL Cluster (NDB).
Proving that MEMORY is/isn’t crash safe around DDL is an exercise left to the reader
Thanks go to Alexey Kopytov for looking into the InnoDB code for this post.
Percona’s widely read Percona Data Performance blog highlights our expertise in enterprise-class software, support, consulting and managed services solutions for both MySQL® and MongoDB® across traditional and cloud-based platforms. The decades of experience represented by our consultants is found daily in numerous and relevant blog posts.
Besides specific database help, the blog also provides notices on upcoming events and webinars.
Want to get weekly updates listing the latest blog posts? Subscribe to our blog now! Submit your email address below.