[mythtv-users] Must mythbackend be running when executing optimize_mythdb.pl and/or mythlink.pl?

[Michael T. Dean]

On 04/06/2012 11:05 AM, Michael T. Dean wrote:
> On 04/06/2012 07:44 AM, Craig Huff wrote:
>> I currently run these scripts as part of my shutdown process on the
>> backend, along with other things.  It seems I'm taking too long
>> shutting down and sometimes mythbackend gets impatient and tries to
>> restart things, occasionally ending up in a deadlock instead of
>> actually shutting down.  In an attempt to fix this, I'm wondering if I
>> can move execution of either (or both) of these scripts to run after
>> mythbackend is killed in the shutdown process sequence.  Can anyone
>> advise me on this?
> mythlink.pl can definitely be run when mythbackend is running without 
> having any effect on the backend or recordings or frontend or playback 
> or ... (assuming your backend host/MySQL server is not severely 
> underpowered).  (Before the support for use in MythTV System 
> Events/user jobs,) I used to run it at 2 and 32 minutes after the 
> hour, every hour, every day (but I almost never use the renamed links, 
> now, so I only run it once per day), and never had any problems.
>
> optimize_mythdb.pl can be run while mythbackend is running, but--as 
> you've noticed--may take a while to complete.  While it's running, it 
> locks tables, preventing other processes (such as mythbackend) from 
> reading or writing those tables.  Therefore, running it when MythTV 
> needs access to the data in the database may cause issues (including 
> loss of some data for the new recording(s)).  So, we highly recommend 
> that you run the script at some time when it's extremely unlikely that 
> you'll be doing a recording.  I run it in a daily cron job that occurs 
> at 4:38am.
>
> Also, the only reason we don't automatically run optimize_mythdb.pl 
> type functionality (repair/analyze/optimize)--we already have code in 
> MythTV to do it all--is because if it were being run and the MySQL 
> server crashes (mysqld crash/power outage/full file system/...) during 
> a table repair, it's critical that a repair is run, again, after 
> restarting the server and before any client attempts to read any data 
> from the table that was being repaired--otherwise, you could lose all 
> of the data in the table.  Therefore, since we can't guarantee that 
> we'll be able to run the repair before anyone else reads from the 
> table before, and because even doing a quick check to see if tables 
> are good before starting the master backend slowed startup 
> sufficiently, on some systems, that we had to remove the check.  That 
> means repair/analyze/optimize are left to the user/"db admin" for the 
> system.  And, if there's a database crash, you should probably shut 
> down all MythTV applications, then do an optimize_mythdb.pl or 
> mysqlcheck -r before restarting MythTV (really, that's a good idea any 
> time there's a MySQL crash, even if you weren't running a repair at 
> the time).  (Unfortunately, currently optmize_mythdb.pl requires a 
> working settings table, so if your settings table is crashed, you'll 
> need to run mysqlcheck -r directly--and figure out all the right 
> command-line arguments.  I'm hoping to fix that, sometime.)

Seems you wanted to know the opposite--whether you can run the scripts 
when the master backend is not running.  I /think/ both of them will 
only work when the master backend is running because they use the 
bindings to connect to the master backend to get the database connection 
information (though they attempt to create a MythTV object without a 
connection to allow use without a running master backend, I'm thinking I 
noticed that they don't work without the MBE--at least in some 
configurations, depending on how your DB connection information is 
specified).  However, I can say that not running the backend will not 
hurt the scripts at all--so the best way to find out is to try (and then 
let us know what you find).

Mike