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". 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.