[Kea-users] mysql innodb_flush_log_at_trx_commit=2

[Jaco Kroon]

Hi,

https://kea.readthedocs.io/en/latest/arm/admin.html#upgrading-a-mysql-database-from-an-earlier-version-of-kea

There is a correction to the warning that warrants investigation:

a value of =2 (or even =0) is only a risk on *host* (kernel) crash. The 
only thing that changes is that mysql/mariadb will not execute an 
fsync() as frequently.  So the stability of kea has no effect here.

Writes are still done in-order etc.  However, when using replication, 
it's pretty much a guarantee that you'll need to rebuild the crashed 
host from the replica.  The WAL is also affected by same and due to lack 
of fsync() write-ordering (which is important for resilience) is not 
guaranteed.

Someone may just want to look into the documentation here.

If kea uses multiple-threads towards mysql/mariadb, group commits is 
another way to boost performance, this can be achieved by just 
increasing the concurrency of threads towards mysql/mariadb - a bunch of 
other parameters (like max connections etc) may also need to be tweaked.

The single biggest win for mysql/mariadb is a battery-backed 
write-behind raid controller.

Compared to KEA I consider the Linux kernel to be significantly more 
stable, however, crashes do happen, but please be sure that the 
documentation reflects correctly, kea crashing has no effect on 
mysql/mariadb consistency, and even mysql/mariadb crashes (should afaik) 
not impact this stability, only host crashes where issued write()s don't 
make it to disk.

Kind regards,
Jaco