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Old 11-01-2015, 10:33 PM
Akkadius's Avatar
Join Date: Feb 2009
Location: MN
Posts: 2,013
Default Perl Footprint Adjustment

I wanted to make a post to create awareness around the last commit I made regarding Perl. It really shouldn't change any existing functionality but only improve performance (exponentially) and I wanted to let people know why these changes were made and what for.

In summary: When Perl triggers a sub event, it goes through calculating and exporting quite a few variables at runtime and this can pose performance issues as your server starts to grow and events are triggered constantly. This does not pose an issue at all on LUA because LUA does not export things at runtime all the time, why would you when you don't use 95% of the variables most of the time in a given sub event.

- That is the reason why you would use "GetThing()" versus using $getthing, GetThing() is going to get that when it needs it versus $getthing is getting created regardless whether or not you use it in a script, times that by a few thousand variables depending on your scenario and it really starts to pose overhead issues.

- Item variables get exported in every single subroutine but they are only used in EVENT_ITEM and EVENT_SAY and maybe a few other rare sub events that I found on PEQ quest repository (that are turned on in the default table provided).

- If anyone has any questions regarding any of this let me know, I've ran it on EZ and seen substantial improvement. All of the notes are below.


From Changelog:

Akkadius: Added Perl Export Settings which should heavily reduce the Perl footprint
	- Normally when any sub EVENT_ gets triggered, all kinds of variables have to get exported every single time an event is triggered and 
		this can make Perl very slow when events are triggered constantly
			- The two most taxing variable exports are the item variables ($itemcount{} $hasitem{} $oncursor{}) and qglobals ($qglobals{})
			- qglobals can pose to be an issue quickly when global qglobals build up, it is highly recommend to use the GetGlobal() and SetGlobal()
				methods instead as they don't reference the hashmap $qglobals{} that is rebuilt every single time a sub event is triggered
	- A stress test conducted with 10,000 samples shows an excess of time taken to export variables: http://i.imgur.com/NEpW1tS.png
	- After the Perl Export Settings table is implemented, and all exports are shut off you see the following test result:
	- The difference of eliminating uneeded exports brings the overhead and footprint of 10,000 triggers from 54 seconds to 2 seconds
	- In a 10,000 sample test (10,000 sub event triggers), exporting item variables adds 12 seconds alone, when item variables are only needed in
		EVENT_ITEM and EVENT_SAY a majority of the time if at all
	- In a 10,000 sample test (10,000 sub event triggers), exporting qglobals with approximately 1,000 global qglobals in the database creates
		about 11-20 seconds of delay on its own (Depending on hardware of course)
	- I've written a parser that has determined which of these exports are needed in which sub routines and have turned off all of the unneeded
		exports in sub routines that do not need them and used it to create the default table that will be installed in the database.
	- The export table is called 'perl_event_export_settings' and it resembles the following structure and contains all current 81 EVENTS
		- If an entry doesn't exist in this table and a new subroutine is added to the source, all exports will be on by default for that routine

	| event_id | event_description                       | export_qglobals | export_mob | export_zone | export_item | export_event |
	|        0 | EVENT_SAY                               |               1 |          1 |           1 |           1 |            1 |
	|        1 | EVENT_ITEM                              |               1 |          1 |           1 |           0 |            1 |
	|        2 | EVENT_DEATH                             |               1 |          1 |           1 |           0 |            1 |
	|        3 | EVENT_SPAWN                             |               1 |          1 |           1 |           0 |            1 |
	|        4 | EVENT_ATTACK                            |               0 |          1 |           1 |           0 |            1 |
	|        5 | EVENT_COMBAT                            |               1 |          1 |           1 |           0 |            1 |
	- If a change is made to this table while the server is live and running, you can hot reload all zone process settings via:
	- For those who wonder what "exports" are, they are reference to variables that are made available at runtime of the sub event, such as:
		(export_qglobals) (Heavy) : $qglobals https://github.com/EQEmu/Server/blob...arser.cpp#L916
		(export_item) (Heavy) : $itemcount{} $hasitem{} $oncursor{} https://github.com/EQEmu/Server/blob...rser.cpp#L1103
		(export_zone) : $zoneid, $instanceid, $zoneln etc. https://github.com/EQEmu/Server/blob...rser.cpp#L1083
		(export_mob) : $x, $y, $z, $h, $hpratio etc. https://github.com/EQEmu/Server/blob...rser.cpp#L1032
		(export_event) : (event specific) IE: EVENT_SAY ($text) https://github.com/EQEmu/Server/blob...rser.cpp#L1141
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