User:Becky Pippen/Memory Efficiency - Revision history

Kizmut Smit: +cat :3

2014-03-31T22:39:30Z

+cat :3

← Older revision		Revision as of 15:39, 31 March 2014
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	make realistic goals for reducing memory usage. For some suggestions for specific scripting techniques,		make realistic goals for reducing memory usage. For some suggestions for specific scripting techniques,
	see [[User:Becky_Pippen/Script_Memory_Limits\| this checklist of things you can do]].		see [[User:Becky_Pippen/Script_Memory_Limits\| this checklist of things you can do]].

			{{Resource Conservation Portal Nav\|cat=memory}}

Becky Pippen: minor formatting

2010-01-06T21:19:31Z

minor formatting

← Older revision		Revision as of 14:19, 6 January 2010
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	the data gets rounded off to <0.57, 0.20, 0.99>. In that case, each of the three components can take		the data gets rounded off to <0.57, 0.20, 0.99>. In that case, each of the three components can take
	one of 101 possible values (0.00 through 1.00 with 0.01 resolution), and the information content is		one of 101 possible values (0.00 through 1.00 with 0.01 resolution), and the information content is
	then 3 * log2(101) = 20 bits. If stored in a list, the efficiency would drop to 20 / 224 = 9%. Ouch.		then 3 * log2(101) = 20 bits. If regular vectors are stored in a list, the efficiency would drop to 20 / 224 = 9%. Ouch.

	==== Example #3 - UUIDs in a global list ====		==== Example #3 - UUIDs in a global list ====
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	of information, the theoretical minimum memory requirement would be 1000*16 = 16000 bytes, well within		of information, the theoretical minimum memory requirement would be 1000*16 = 16000 bytes, well within
	the capacity of a Mono script.		the capacity of a Mono script.

			===Now what?===

	Now that you know the minimum amount of memory needed and the amount actually used, you can		Now that you know the minimum amount of memory needed and the amount actually used, you can
	make realistic goals for reducing memory usage. For some suggestions for specific scripting techniques,		make realistic goals for reducing memory usage. For some suggestions for specific scripting techniques,
	see [[User:Becky_Pippen/Script_Memory_Limits\| this checklist of things you can do]].		see [[User:Becky_Pippen/Script_Memory_Limits\| this checklist of things you can do]].

Becky Pippen at 20:52, 31 December 2009

2009-12-31T20:52:46Z

← Older revision		Revision as of 13:52, 31 December 2009
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	The memory efficiency is simply the information content divided by the actual memory used. Here are some examples:		The memory efficiency is simply the information content divided by the actual memory used. Here are some examples:

	==== Example #1 - ASCII text ====		==== Example #1 - 7-bit ASCII text ====

	In classic LSO (the old LSL compiler), it takes one byte of memory (8 bits) to hold one ASCII character ~~(7 bits)~~		In classic LSO (the old LSL compiler), it takes one byte of memory (8 bits) to hold one 7-bit ASCII character
	for an efficieny of 7/8 = 88%. In Mono, it takes two bytes (16 bits) to hold each character for an efficiency		for an efficieny of 7/8 = 88%. In Mono, it takes two bytes (16 bits) to hold each ASCII character for an efficiency
	of 7/16 = 44%.		of 7/16 = 44%.

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	the memory available to a single Mono script. However, since each UUID contains only 16 bytes (128 bits)		the memory available to a single Mono script. However, since each UUID contains only 16 bytes (128 bits)
	of information, the theoretical minimum memory requirement would be 1000*16 = 16000 bytes, well within		of information, the theoretical minimum memory requirement would be 1000*16 = 16000 bytes, well within
	the capacity of a Mono script. Now ~~all we need is to find some way to get closer to~~ that ~~theoretical~~ minimum.		the capacity of a Mono script.
	For some suggestions, see [[User:Becky_Pippen/Script_Memory_Limits\| this checklist of things you can do]].
			Now that you know the minimum amount of memory needed and the amount actually used, you can
			make realistic goals for reducing memory usage. For some suggestions for specific scripting techniques,
			see [[User:Becky_Pippen/Script_Memory_Limits\| this checklist of things you can do]].

Becky Pippen: preliminary page in anticipation of script memory limits

2009-12-30T23:18:33Z

preliminary page in anticipation of script memory limits

New page

== Information Content and Memory Efficiency ==

For a refresher on relevant information theory, see [http://www.cs.cmu.edu/~dst/Tutorials/Info-Theory/ this tutorial].

It's useful to understand the "information content" of data so that you can calculate
the theoretical minimum number of bits needed to store the data. Typically it's the
logarithm base two of the total number of possible values the data can have. Here are
some examples:

* coin toss: log2(2) = 1 bit per toss
* 6-sided die toss: log2(6) = 2.585 bits per toss
* integers 0 through 100: log2(101) = 6.66 bits each
* 32-bit integers, non-negative values: log2(2147483648) = 31 bits each
* 32-bit integers, all possible values: log2(4294967296) = 32 bits each

The actual memory space used by various LSL data types can be found here:
* [http://lslwiki.net/lslwiki/wakka.php?wakka=MemoryUsage LSL Memory Usage in lswiki.net]
* [[LSL_Script_Memory|Script memory usage in wiki.secondlife.com]]

The memory efficiency is simply the information content divided by the actual memory used. Here are some examples:

==== Example #1 - ASCII text ====

In classic LSO (the old LSL compiler), it takes one byte of memory (8 bits) to hold one ASCII character (7 bits)
for an efficieny of 7/8 = 88%. In Mono, it takes two bytes (16 bits) to hold each character for an efficiency
of 7/16 = 44%.

==== Example #2 - Vectors in a global list ====

The information content of a vector is the equivalent of three floats, or 3 * 32 bits = 96 bits per vector.
A list in Mono consumes 224 bits for each vector element for an efficiency of 96 / 224 = 43%. Note that if you only
need to store a smaller range of values in each vector component, the information content will be smaller.
For example, suppose you need to store a color vector with two decimal digits of accuracy for each component.
In other words, instead of precision like <0.567876, 0.198273, 0.993656>, it's sufficient for your purposes if
the data gets rounded off to <0.57, 0.20, 0.99>. In that case, each of the three components can take
one of 101 possible values (0.00 through 1.00 with 0.01 resolution), and the information content is
then 3 * log2(101) = 20 bits. If stored in a list, the efficiency would drop to 20 / 224 = 9%. Ouch.

==== Example #3 - UUIDs in a global list ====

The information content of a UUID is 128 bits. In a global list in Mono, each key takes up to 106 bytes (848 bits)
for an efficiency of 128 / 848 = 15%. Suppose your script needs to store
up to 1000 avatar UUIDs in a global list. That's going to use up 1000*106 bytes = 106,000 bytes, more than
the memory available to a single Mono script. However, since each UUID contains only 16 bytes (128 bits)
of information, the theoretical minimum memory requirement would be 1000*16 = 16000 bytes, well within
the capacity of a Mono script. Now all we need is to find some way to get closer to that theoretical minimum.
For some suggestions, see [[User:Becky_Pippen/Script_Memory_Limits| this checklist of things you can do]].