[mythtv-users] Bad mysql performance -- huge oldrecorded -- joins without index

Michael T. Dean mtdean at thirdcontact.com
Wed Jun 8 15:13:38 UTC 2016

On 06/08/2016 10:42 AM, Simon Hobson wrote:
> "Michael T. Dean" wrote:
>> There is one way to improve scheduler performance outside of MythTV--4) throw more/better resources at it:  get better/more CPU and/or RAM and/or file system performance (which can have a huge impact if using things like barriers or file systems that take huge amounts of I/O resources when doing things like deleting large files and when the user didn't enable slow deletes in MythTV, like he should have).
> So the first step is, as the OP seems already to be doing, tune MySQL to the load and use as much RAM as "makes sense" - there is a point where adding RAM makes little additional difference, but initially a bit more RAM can make a huge difference.

Yes, this is definitely important, too--and may well be a large part of 
the problem.  There's nothing MythTV is doing that requires a 
supercomputer, so given a reasonable computer for running MythTV, 
performance should be good for any "residential" use case.

I will also say that file system choice/configuration (especially in 
regards to blocking due to barriers***) for the file system holding the 
MySQL binary data files and MySQL configuration (especially with the 
InnoDB storage engine that many are using) are often bad on many systems 
out there.  That said, a proper discussion of the 
issues/considerations/... involved when it comes to MySQL would make my 
previous reply (a short novel), which focused only on the MythTV-related 
aspects, look like a short tweet in comparison. Therefore, I took the 
easy way out and ignored the MySQL aspect.


*** Note, too, that I am not saying to disable barriers on the file 
system used to store MySQL data files, nor on any other.

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