[rules-users] 答复: Performance consideration in rule writing

[Wolfgang Laun]

On 26/12/2011, Zhuo Li <milanello1998 at gmail.com> wrote:
> //Abe: it definitely makes a difference if you put differentiator conditions
> at the beginning ¨C this way RETE won¡¯t waste efforts constructing networks
> which will not fulfill. See below example.
>
> rule "Evaluation of assignment in r-value position"
> no-loop true
> when
>  $statement:CStatement($value:value)
>  eval(Matcher.isRVExpression($value))
>
>  eval(0==Matcher.getClauseNum())
> then
>  System.out.println($value);
>  modify($statement){
>   setSemantics(Matcher.getRVSemantics(memory,$value));
>  }
> end
>
> rule "Evaluation of assignment clause in r-value position without updating
> memory"
> no-loop true
> when
>  $statement:CStatement($value:value)
>  eval(Matcher.isRVExpression($value))
>
>  eval(0<Matcher.getClauseNum())
> then
>  System.out.println("=="+$value);
>  Matcher.decreaseClauseNum();
>  modify($statement){
>   setSemantics(Matcher.getRVSemanticsWithoutUpdate(memory,$value));
>  }
> end
>

This is quite different from the rules in the original post. It is
generally not advisable to access and modify static variables, here:
clauseNum in class Matcher, i.e., not a fact.


>

>  //Abe: I saw below statement from Drools document 5.2.0. As Eval is not
> indexed, overuse of evale reduces the rules¡¯ clarity and will result in a
> bad performance.

Needlessly using eval is not good; if you have to use it you won't be
able to avoid it.


>
>
> 3.       What¡¯s you guys¡¯ naming convention for rule¡¯s salience?
>
> Not clear what you mean by that.
>
> //Abe: I mean how do you weight your salience values across different rules.
> I¡¯ve seen various styles in my project ¨C somebody uses 100, 200, 300 but
> somebody uses 90, 100, 110, 120, etc. This is not a big problem as they are
> working on different rules and won¡¯t pollute each other. However I would
> still try to make it consistent so maintain each other¡¯s rule files will be
> easier¡­

Making your rules depend on salience isn't good practice, certainly
not with more than 3 levels (my personal definition). The sort of
multi-level salience you're indicating could be an indication that
procedural style if-then-elsif logic has been fitted into rules.

-W
>
>
>
> ·¢¼þÈË: rules-users-bounces at lists.jboss.org
> [mailto:rules-users-bounces at lists.jboss.org] ´ú±í Wolfgang Laun
> ·¢ËÍʱ¼ä: 2011Äê12ÔÂ26ÈÕ 22:20
> ÊÕ¼þÈË: Rules Users List
> Ö÷Ìâ: Re: [rules-users] Performance consideration in rule writing
>
>
>
> See below.
>
> 2011/12/26 Zhuo Li <milanello1998 at gmail.com>
>
> Hi, team,
>
>
>
> I have some quick questions here regarding performance best practices of
> rule writing. See below two pieces of rules:
>
>
>
> Rule ¡°1¡±
>
>          Salience 100
>
>          No-loop true
>
>          When $txn : data(sourceid == 5&&txnjustify==¡±995¡±
> &&eval(creditOption($txn)==1)&&eval(isGCSwitch($txn))&&isCurrencyEquals($txn
> )==0&&compareToPostThreshold($txn)==2);
>
>          Then
>
>                    ¡­
>
>          End
>
>
>
> Rule ¡°2¡±
>
>          Salience 100
>
>          No-loop true
>
>          When $txn : data(sourceid == 5&&txnjustify==¡±995¡±
> &&eval(creditOption($txn)==1)&&eval(isGCSwitch($txn))&&isCurrencyEquals($txn
> )==0&&compareToPostThreshold($txn)==1);
>
>          Then
>
>                   ¡­
>
>          End
>
>
>
> Questions:
>
> 1.       Will I gain better performance if I put the rule differentiator
> condition ¡°compareToPostThreshold($txn)==2¡± at the beginning of both rule
> 1 and 2?
>
> One kind pf Rete optimization is based on evaluating common constraints
> once, therefore: no.
>
>
> 2.       I saw salaboy¡¯s video claiming that to avoid using eval() in the
> rule. Do we have any alternative way to do that from a performance
> consideration
>
> Constraints based on fields using == are best. Other things may result in
> eval-like evaluations anyway. Most of the time, it isn't eval that causes
> performance setbacks.
>
> or I¡¯d better collect/ prepare all the data before I send them into the
> session?
>
> Not clear what you mean by this, but if you can provide attributes that lend
> themselves to straightforward constraints it might be worthwhile considering
> some up-front processing of facts.
>
>
> 3.       What¡¯s you guys¡¯ naming convention for rule¡¯s salience?
>
> Not clear what you mean by that.
>
> -W
>
>
>
>
> PS: my Drools version is 5.2.0.
>
>
>
> Best regards
>
> Abe
>
>
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