[mythtv-users] "Watch Recordings" slow - disable thumbnail/preview generation, or big SQL queries?

Niklas Brunlid prefect47 at gmail.com
Mon Apr 4 16:42:27 UTC 2011

On 2 April 2011 20:46, Michael T. Dean <mtdean at thirdcontact.com> wrote:

> To see if you're having data-access problems, try running:
> wget 'http://<masterbackendip>:6544/Myth/GetRecorded' -O /dev/null
> (but change "<masterbackendip>" to the IP address of your master
> backend).  After, you should see something like (probably about 2x as
> large as since I have 1469 recordings):
> 100%[======================================>] 1,263,278   --.-K/s   in 0.1s
> If so--if you're getting the results in, say, 0.2s or 0.3s--the problem
> is likely the mythfrontend sorting/processing of those recordings.
> FWIW, with half as many recordings as you have, my system brings up the
> Watch Recordings screen in (seemingly a lot less than) 0.5s (I'd guess
> 0.2 to 0.3s, but can't say for sure).  So, either you've surpassed some
> performance ceiling, have an underpowered frontend (mine is not an
> Atom--it's a real computer--but trying to load that screen with 3K
> recordings on an Atom-based system *should* take a long time), or have
> some other misconfiguration, such as...

> Often previews /are/ a problem for users with some MythTV system
> misconfigurations--but, as Raymond  mentioned, won't be a problem on a
> properly-configured system.
> Off the top of my head, reasons I can remember that cause previews to
> slow Watch Recordings include:
>   a) having your (frontend user) $HOME/.mythtv directory on NFS and
> disabling file-attribute caching
>   b) having a broken/not-writable $HOME/.mythtv/{remote,theme}cache
> directory
>   c) having a time difference on your frontend and backend machines
> (you should use NTP on all mythtv machines)
> There are probably others, too,  but this is a good start of a list of
> things to look at.
$ time wget 'http://<address>:6544/Myth/GetRecorded' -O /dev/null
--2011-04-04 18:28:38--  http://<address>:6544/Myth/GetRecorded
Connecting to <address>:6544... connected.
HTTP request sent, awaiting response... 200 OK
Length: 2956015 (2.8M) [text/xml]
Saving to: /dev/null

100%[======================================>] 2,956,015   --.-K/s   in 0.01s

2011-04-04 18:28:44 (291 MB/s) - /dev/null

real    0m5.801s
user    0m0.001s
sys     0m0.007s

So the actual download goes by quickly, but it takes a few seconds before it
starts to receive data.

System specs: Fedora 13 on an Asus K8V with an AMD64 3000+ and a Sparkle
GeForce 9400 GT PCI card, with OpenGL painter and VDPAU output, using
DVI->HDMI to a FullHD LCD TV and the SP/DIF of the mainboard directly to the
amplifier. The system is somewhat regularly updated against the Fedora and
ATrpms repos. MythTV version is release-0-22-fixes 22973.

Everything runs on the same computer, no external file systems, everything
on ext3. Recording drives have "rw,data=writeback" flags, used to have
noatime and nodiratime but those were removed since I suspected they
interfered with thumbnail generation.

Is $HOME in (b) above for mythfrontend or mythbackend? The frontend runs as
my normal user, the backend runs as root. In the user home remotecache and
themecache are writable by user and group, in root:s home I only have
themecache and it's writable by root only.

/ Niklas
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