[kdepim-users] changing database backend

Pablo Sanchez pablo at blueoakdb.com
Wed Nov 12 14:54:20 GMT 2014

[ Comments below, in-line ]

On 11/12/2014 09:11 AM, René J.V. Bertin wrote:
> I must have been unclear - my idea of changing concerned my Linux
> rigs because those run on ZFS. You're undoubtedly aware that you
> disable COW on btrfs (I suppose for performance reasons). That's
> highly "not done" on ZFS and thus impossible, but also much less
> necessary because of internal optimisation (or so I have been told).
> Either way, it makes sense to disable COW-like features in software
> when it write to a filesystem that already implements it. MySQL
> allows that by setting innodb_doublewrite=0 . I'd compare the other
> option but 1) I'd have to start the server myself and 2) no way if
> I'd have to redo the whole of akonadi again...


If you're willing to /potentially/ compromise data integrity, you can
disable database logging (to some extent).  Except for the hardest of
hardware failures, you'll /probably/ be okay.

Another way to say this, if you're willing to tolerate some data loss
and/or database inconsistency, then disable logging.  I wouldn't do
it.  I'd rather buy an SSD (cheap!) and not worry about I/O.

The documentation for /innodb_doublewrite/ parameter explicity states:

   This variable can be turned off with --skip-innodb_doublewrite for
   benchmarks or cases when top performance is needed rather than
   concern for data integrity or possible failures.

In order for the DBMS to conform to ACID [1], you can't disable
logging.  :)

If you want more information about MySQL and the ACID Model, see this


   ... you can adjust MySQL settings to trade some of the ACID
   reliability for greater performance or throughput.

[1] - http://en.wikipedia.org/wiki/ACID

Pablo Sanchez - Blueoak Database Engineering, Inc
Ph:    819.459.1926         Blog:  http://pablo-blog.blueoakdb.com
iNum:  883.5100.0990.1054

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