[mythtv-users] slow mythweb?

Udo van den Heuvel udovdh at xs4all.nl
Mon Apr 21 17:13:19 UTC 2008


Michael T. Dean wrote:
> On 04/21/2008 09:53 AM, Jens Baumeister wrote:
>> Considering the extreme nature of your recording schedule, you're
>> apprently running into some kind of bottleneck, but I have no idea
>> which one.
> 
> The more shows you have scheduled to record, the longer scheduling 
> takes.

Why?
Only fetching info on one more programs is required, for only 3 channels
at the most at the same time.

> Though the scheduler query may not be taking a lot of time, 
> that's only part of the scheduling process.  In the event that your 
> grabber provides programid's, the scheduler query will be the fast part 
> of scheduling.

How would I know if I get programid's and what/how do they help?

> same as pre-multirec (maybe a little better).  The one distinction, 
> however, is that with multirec, a user can enable significantly more 
> recordings than they could in pre-multirec.

Only three at any time, maybe 6 max with the 1 minute extra at the start
and end of a show.

>  Therefore, users can create 
> situations where their (especially, low-powered) systems can't handle 
> the scheduling sufficiently quickly.  See 
> http://www.gossamer-threads.com/lists/mythtv/dev/294301#294301 and the 
> entire (5 page) thread at 
> http://www.gossamer-threads.com/lists/mythtv/commits/265142#265142 (and 
> many more posts about scheduler performance during the development of 
> multirec).

I can't see why the amount of data required for scheduling a few shows
on a database that fits easily in memory would cause such a CPU-load.
The database does, however, show the strange issues I posted about. How
can a database use over 10 times it's size in temp space?
This must be a strange bug.

> So, like Jens said, it's quite likely that your pushing your system to 
> an extreme is what's causing the performance issue--you're simply trying 
> to do too much recording with too little MythTV resources.  

1 multiplex, three TV channels with only a few megabits of data per
second (it's low bitrate TV...).
There is enough RAM and a quitably quick SATA disk.

If you
> really want to record everything with that system, you may need to find 
> another program to do it.  Or, you can get a better system.  Or, you can 
> try more systems (though you'll almost definitely need a more powerful 
> master backend--as it's the one that does the scheduling).

For recording only three channels I need more than this Epia?!
What is the bottleneck?
When mythbackend stops responding (it just did again) there is plenty of
CPU, plenty of RAM (used for caching, 500megs+) and the processlist
looks like this:

mysql> show processlist;
+-----+--------+-----------+-------------+---------+------+-------+------------------+
| Id  | User   | Host      | db          | Command | Time | State | Info
            |
+-----+--------+-----------+-------------+---------+------+-------+------------------+
| 679 | mythtv | localhost | mythconverg | Sleep   | 5860 |       | NULL
            |
| 681 | mythtv | localhost | mythconverg | Sleep   | 5852 |       | NULL
            |
| 682 | mythtv | localhost | mythconverg | Sleep   | 5988 |       | NULL
            |
| 692 | mythtv | localhost | mythconverg | Sleep   | 5817 |       | NULL
            |
| 693 | mythtv | localhost | mythconverg | Sleep   | 5860 |       | NULL
            |
| 935 | mythtv | localhost | mythconverg | Sleep   | 5783 |       | NULL
            |
| 936 | mythtv | localhost | mythconverg | Sleep   | 5634 |       | NULL
            |
| 937 | mythtv | localhost | mythconverg | Sleep   | 5599 |       | NULL
            |
| 938 | mythtv | localhost | mythconverg | Sleep   | 5517 |       | NULL
            |
| 939 | mythtv | localhost | mythconverg | Sleep   | 5482 |       | NULL
            |
| 940 | mythtv | localhost | mythconverg | Sleep   |   43 |       | NULL
            |
| 941 | mythtv | localhost | mythconverg | Sleep   |   43 |       | NULL
            |
| 942 | root   | localhost | NULL        | Query   |    0 | NULL  | show
processlist |
+-----+--------+-----------+-------------+---------+------+-------+------------------+
13 rows in set (0.00 sec)

There is no errors, no complaints in mythbackend.log, messages or
anything. Don't you think this is strange if the system behaves as
described?

I don't see why there should be a problem for gathering the required
data for recording three shows at a time, streaming a few megabits and
avoiding the stoping behaviour I notice on this system.
My firewall streams more megabits and has less CPU and less RAM.
What is the bottleneck?
Why is so much database action going on? Why does it take so long even
though the whole database is in RAM, more or less? (see tuning-primer.sh)
Why are the temp tables so big? (way bigger than 10 timest he database
as a whole)

This is not yet a system restriction but perhaps a design issue or bug.
I don't know, but strange it is.


Udo


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