[rules-dev] Lazily Enabled Truth Maintenace (Project Propsoal)

[Mark Proctor]

  On 15/09/2010 14:35, Michael Anstis wrote:
> Is this in drools-core; or drools-compiler?
>
> Whilst not undertaking to do the work; have a purpose to nose through 
> the code makes understanding easier.
It's all in DroolsCore.

It's a 5 minute hack for me and then 15 minute unit writing test. But I 
thought I'd write it up in a hope to bring someone else into the fold, 
we need more help writting the core engine someone else out there must 
want to work on current edge engine design :)

if you look at the AbstractWorkingMemory insert method you'll see one 
argument is whether it's a logical insertion or not. You'll also see it 
check the global maintainTMS configuration and also retrieve the 
ObjectTypeConf. So between those things someone should be able to get it 
working.

Mark
>
> On 14 September 2010 16:47, Mark Proctor <mproctor at codehaus.org 
> <mailto:mproctor at codehaus.org>> wrote:
>
>     Here is another project proposal, this time simpler. I think this
>     one has Wolfgang's name on it ;)
>
>     http://blog.athico.com/2010/09/lazily-enabled-truth-maintenace.html
>
>     Three weeks ago I posted the project idea for "Left and Right
>     Unlinking"
>     <http://blog.athico.com/2010/08/left-and-right-unlinking-community.html>.
>     So far there are no takers, so if you are interested let me know :)
>
>     In the meantime I tried to think of a simpler enhancement that we
>     would like to see done.
>
>     At the moment Drools has a user setting "MaintainTMSOption" which
>     can be true or false. It's a small optimisation that when turned
>     off avoids using the equality hashmap that is maintained for all
>     inserted objects.
>
>     It would be a much better idea to remove this configuration
>     setting, thus simplifying things for end users and have TMS lazily
>     enabled on demand.
>
>     For each object type there is an "ObjectTypeConf" configuration
>     object that is retrieved every time a working memory action, such
>     as insert, is executed. The enabledTMS boolean should be moved
>     there, so there is one per object type, by default it is false.
>
>     When a working memory action occurs, like insert, it retrieved the
>     ObjectTypeConf and checks the maintainTms boolean there, instead
>     of the current engine scoped configuration. When a logical
>     insertion occurs and the ObjectTypeConf is retrieved if
>     maintainTms is false it sets the value to true and then iterates
>     the associated ObjectTypeNode memory lazily adding all the objects
>     to the TMS equality map. From then on for that ObjectType all
>     inserted objects are added to that equality map.
>
>     With this you now have the advantage of TMS being laziy enabled,
>     so the minor hashmap operation is no longer used and likewise a
>     small memory saving from not populating the map. There is a
>     further advantage that this is now fine grained and when enabled
>     only impacts for that specific object type.
>
>     A further enhancement could use a int counter, instead of a
>     boolean. Each logical insertion for that object type increases the
>     counter, each retraction decreases the counter; even if
>     automatically retracted if the truth is broken for that logical
>     assertion. When the counter reaches zero, TMS for that OTN can be
>     disabled. We do not however remove the objects from the equality
>     map, as this would cause "churn" if TMS is continuously enabled
>     and disabled. Instead when TMS is disabled record the current fact
>     counter id. Then if TMS is disabled on a retraction but there is a
>     counter id, we can check that counter id to see if the fact is
>     prior to TMS being disabled and thus would need to be retracted
>     from the equality map.
>
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