[mythtv-users] Database tuning

[Keith Pyle]

On 09/01/13 07:00, Simon Hobson wrote:

...

> But still, if there's enough mamory to hold all the tables and indexes in memory, then I don't see why it appears to be creating 200+M of "something" on disk and creating a lot of wait I/O which seems to be my problem.
>
> It also causes pauses in playback when recordings start and end - last night I had my iPad handy so was able to check - and each time a recording started or ended, there was a pause (several seconds) in playback. That'll be because the database (and OS) is on the same disks as the recordings (but not for long*) - however that's a symptom of the underlying problem rather than the problem itself.
>
> * Ebuyer just had a too good to pass up deal on SSDs, so the OS and database will soon be on an SSD.
Having your DB on a SSD will definitely improve responsiveness.  I have 
a SSD in my backend for the OS and DB, and it presented a noticeable 
improvement when I switched from a conventional drive. There were some 
people concerned that a high write load from a DB would wear out a SSD 
too fast.  My backend SSD has 3.995 years of power-on time and smartctl 
shows the 'media wear-out indicator' at 97 out of 100.  So, there's no 
real issue in terms of media wear from the MythTV DB on the SSD.

The SSD alone will likely help if your performance issue is due to disk 
I/O.  However, you should consider creating a tmpfs for /tmp if you feel 
there is sufficient memory in the system.  I use a 1 GB tmpfs, but 500 
MB might be sufficient for your use. If /tmp is on a tmpfs, your I/O for 
temporary tables should be even faster than what you can achieve with a SSD.

Keith