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Re: Waiting for commit lock
Posted by: Mikael Ronström
Date: July 14, 2017 05:51PM

Here is a cut from the manual on how mysqldump works:

This backup operation acquires a global read lock on all tables at the beginning of the dump (using FLUSH TABLES WITH READ LOCK). As soon as this lock has been acquired, the binary log coordinates are read and the lock is released. If long updating statements are running when the FLUSH statement is issued, the backup operation may stall until those statements finish. After that, the dump becomes lock-free and does not disturb reads and writes on the tables.

So during the entire backup operation the entire MySQL Server is
locked such that you can only read data.

This affects also NDB tables since it locks the entire MySQL Server.

So this is the reason why you get this lock.

Backups of NDB data is fully online and requires no locks for read and
write of data. So it is obviously necessary here to consider how you want
to backup non-NDB data in the MySQL Servers used for accessing MySQL Cluster
data.

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