1:56 p.m.
It's common Rete wisdom to order patterns by expected frequency of
matches, in descending order.
Does this also apply to constraints within a single pattern? For
example, is it better to write, for a New York address
Address( street == "Broadway", number == 1)
than
Address( number == 1, street == "Broadway")
or is this irrelevant?
Or does it depend on either constraint (on each own) also occurring in
another rule without the other one?
I guess this could also depend on the implementation, i.e., how
fine-grainedly condition sharing is being done.
Cheers
Wolfgang
6:55 p.m.
On 08/04/2010 19:56, Wolfgang Laun wrote:
It's common Rete wisdom to order patterns by expected frequency
of
matches, in descending order.
Does this also apply to constraints within a single pattern? For
example, is it better to write, for a New York address
Address( street == "Broadway", number == 1)
than
Address( number == 1, street == "Broadway")
or is this irrelevant?
Drools will iterate to find the first == constraints, both literal and
vairable constraints. So if != or < are first, that doesn't matter. For
multiple literal constraints, should definitely have the strongest
descriminator first - although it's not quite that simple. You also want
the descriminator that provides the highest chances of node share
amoung. == literal constraints are hashed so the wider the want out
(alternative values) the more scalable performance you'll see. Drools
actually attempts to hash the fanout of consequence child nodes in the
alpha network, if they to are ==, but rarely is there any real gain from
this as after the first level of descrimination there is general not a
consequence wide fanout based on the previous constraints value.
There are deterministic algorithms that claim to analyse a network to
re-order literal constraints to maximise node sharing, but that's not
something we have, patches please :)
If it's a variable constraint we support composite indexing. Drools
produces a composite index based on the first 3 == constraints. Whether
the order of those first 3 impacts perf, not sure. But if there was a
4th variable constraint and that was the strongest descriminator, it
would get left out of the index; when in reality it's probably the most
important constraint as part of the index.
Mark
Or does it depend on either constraint (on each own) also occurring
in
another rule without the other one?
I guess this could also depend on the implementation, i.e., how
fine-grainedly condition sharing is being done.
Cheers
Wolfgang
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11:40 p.m.
To sum it up: it doesn't hurt if you put constraints using == against one out of
a wide range of values up front, and chances are good that it will improve
performance.
On Fri, Apr 9, 2010 at 1:55 AM, Mark Proctor <mproctor(a)codehaus.org> wrote:
On 08/04/2010 19:56, Wolfgang Laun wrote:
> It's common Rete wisdom to order patterns by expected frequency of
> matches, in descending order.
s/descending/ascending/ Was I thinking of descending probability? ;-)
Thanks, Mark!
-W
> Does this also apply to constraints within a single pattern? For
> example, is it better to write, for a New York address
> Address( street == "Broadway", number == 1)
> than
> Address( number == 1, street == "Broadway")
> or is this irrelevant?
>
Drools will iterate to find the first == constraints, both literal and
vairable constraints. So if != or < are first, that doesn't matter. For
multiple literal constraints, should definitely have the strongest
descriminator first - although it's not quite that simple. You also want
the descriminator that provides the highest chances of node share
amoung. == literal constraints are hashed so the wider the want out
(alternative values) the more scalable performance you'll see. Drools
actually attempts to hash the fanout of consequence child nodes in the
alpha network, if they to are ==, but rarely is there any real gain from
this as after the first level of descrimination there is general not a
consequence wide fanout based on the previous constraints value.
There are deterministic algorithms that claim to analyse a network to
re-order literal constraints to maximise node sharing, but that's not
something we have, patches please :)
If it's a variable constraint we support composite indexing. Drools
produces a composite index based on the first 3 == constraints. Whether
the order of those first 3 impacts perf, not sure. But if there was a
4th variable constraint and that was the strongest descriminator, it
would get left out of the index; when in reality it's probably the most
important constraint as part of the index.
Mark
> Or does it depend on either constraint (on each own) also occurring in
> another rule without the other one?
>
> I guess this could also depend on the implementation, i.e., how
> fine-grainedly condition sharing is being done.
>
> Cheers
> Wolfgang
> _______________________________________________
> rules-users mailing list
> rules-users(a)lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/rules-users
>
>
>
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