Improve caching to reduce SQL queries

[Rune Petersen <rune@…>]

mythfrontend make allot of SQL queries when when it is launched, and this affects the time it takes to launch the frontend quite significantly when you have a relatively slow master backend.

Allot of the time is spent querying the settings table for a single value at a time, and for querying the keymappings a single key at a time.

I have made 2 PoC patches showing it is possible to to eliminate almost all of these SQL queries which reduces launch time from 18 secs. to 4-5 secs with a Cortes A8 1GHz master backend.

mythtv_poc_improve_caching_of_host_settings.patch:

• Enable caching if settings a little earlier.
• When enabling settings cache query all host specific and global settings from master backend.
• If cache is enabled and a key is not found in the cache don't fall back to querying master backend since we should be synchronized.
• Use HostSettingStorage? instead of HostDBStorage for Settings menus. HostSettingStorage? gets/sets settings via MythDB which is cached. (can be extended to also work with global settings as well)
• Reduces load time by ca. 9 secs. for me.

mythtv_poc_cache_all_keybindings.patch:

• Cache all keymappings and make use of it when binding keys.
• Reduces load time by ca. 4 secs. for me.

I know these patches are little rough, but I would like to know if you are interested in changes along these lines.

[JYA]

thank you for your patch.

please make the new verbosity "debug", not info.

Please follow mythtv coding style: http://www.mythtv.org/wiki/Coding_Standards

in particular braces and spaces

[JYA]

i wonder how initial settings are read when you have options set like starting mythfrontend with -p (to choose the backend etc)

i have strong suspicions it will introduce a regression

[Rune Petersen <rune@…>]

good point, I suspect you may be right.

I'll try the -p option, and see what happens.

[Rune Petersen <rune@…>]

I cannot test the -p option because it doesn't even work without my changes see #12217

[Rune Petersen <rune@…>]

So I managed to test the -p option, and to my surprise It actually does work without any changes.

I did find some other bugs.

mythtv_poc_improve_caching_of_host_settings_v2.patch:

• Implement HostSettingStorage::Save() properly - changes are now saved =)
• Properly detect when a setting doesn't exist HostSettingStorage?(when to use default value).

[Lawrence Rust]

Jean-Yves

This bug is probably fixed by some of the database caching patches that I've proposed (devel/lvr/startup branch). If you have no objection I would like to take this on...

[Stuart Auchterlonie]

Closing all old tickets in trac.

If your issue still persists, please open an issue in Github ​https://github.com/MythTV/mythtv/issues

and reference the existing trac ticket.