Performance Considerations When Using the Rule Engine

This topic discusses how the rule engine performs in various scenarios and with different values for the configuration/tuning parameters.

Fact Types

The rule engine takes less time to access .NET facts than it does to access XML and database facts. If you have a choice of using .NET, XML, or database facts in a policy, you should consider using .NET facts for better performance.

Data Table vs. Data Connection Binding

When the size of the data set is small (fewer than approximately 10 rows), the TypedDataTable binding performs better than the DataConnection binding. When the data set is large (greater than or equal to approximately 10 rows), the DataConnection binding performs better than the TypedDataTable binding. Therefore, you should decide whether to use the DataConnection binding or the TypedDataTable binding based on the estimated size of the data set.

Fact Retrievers

You can write a fact retriever—an object that implements standard methods and typically uses them to supply long-term and slowly changing facts to the rule engine before the policy is executed. The engine caches these facts and uses them over multiple execution cycles. Instead of submitting a static or fairly static fact each time you invoke the rule engine, you should create a fact retriever that submits the fact the first time, and then updates the fact in memory only when it is needed.

Rule Priority

The priority setting for a rule can range on either side of 0, with larger numbers having higher priority. Actions are executed in order from highest priority to lowest priority. When the policy implements forward-chaining behavior by using Assert/Update calls, the chaining can be optimized by using the priority setting. For example, suppose that Rule2 has a dependency on a value that is set by Rule1. Giving Rule1 a higher priority means that Rule2 will execute only after Rule1 fires and updates the value. Conversely, if Rule2 is given a higher priority, it can fire once, and then fire again after Rule1 fires and updates the fact that Rule2 is using in a condition. This may or may not produce the correct results, but clearly firing twice has a performance impact versus firing only once.

Update Calls

The Update function updates a fact that exists in the working memory of the rule engine, and causes all the rules that use the updated fact in conditions to be reevaluated. Update function calls can be expensive, especially if many rules need to be reevaluated because of updating the facts. There are situations where you can avoid having to reevaluate the rules. For example, consider the following rules:

Rule1:

IF PurchaseOrder.Amount > 5   
THEN StatusObj.Flag = true; Update(StatusObj)  

Rule2:

IF PurchaseOrder.Amount <= 5   
THEN StatusObj.Flag = false; Update(StatusObj)  

All remaining rules of the policy use StatusObj.Flag in their conditions. Therefore, when Update is called on the StatusObj object, all the rules will be reevaluated. Whatever the value of the Amount field is, all the rules except Rule1 and Rule2 are evaluated twice, once before the Update call and once after the Update call.

Instead, you could set the value of the flag field to false before you invoke the policy and then use only Rule1 in the policy to set the flag. In this case, Update is called only if the value of the Amount field is greater than 5, and Update is not called if the amount is less than or equal to 5. Therefore, all the rules except Rule1 and Rule2 are evaluated twice only if the value of the Amount field is greater than 5.

Use of Logical OR Operators

The rule engine is optimized for executing logical AND operators and it reconstructs the rule it parsed in a disjunctive normal form so that OR operator is used only at the top level. Using an increasing number of logical OR operators in conditions creates additional permutations that expand the analysis network of the rule engine, and It may take long time for the rule engine to normalize the rule. The following list contains possible workarounds for this issue.

• Modify the rule to be in disjunctive normal form so that the OR operator is only at the top level. Note that developing a rule in disjunctive normal form in Business Rule Composer can be tricky. You may want to consider creating the rule programmatically.

• Develop a helper component that performs the OR operations and returns a Boolean value, and use the component in the rule.

• Consider splitting the rule into multiple rules and have the rules check for a flag set by a previously executed rule or use an object that is asserted by a previously executed rule as shown in the following examples:

  • Rule 1: IF (a == 1 OR a == 3) THEN b = true

    Rule 2: if (b == true) THEN …

  • Rule 1: IF (a == 1 OR a == 3) THEN assert(new c())

    Rule 2: IF (c.flag == true) THEN …

Caching Settings

The rule engine uses two caches. The first one is in the Update service and the second one is in each BizTalk process. The first time a policy is used, the BizTalk process requests the policy information from the Update service. The Update service retrieves the policy information from the Rule Engine database, caches it, and returns the information to the BizTalk process. The BizTalk process creates a policy object based on that information and stores the policy object in a cache when the associated rule engine instance completes executing the policy. When the same policy is invoked again, the BizTalk process reuses the policy object from the cache if one is available in the cache.

Similarly, if the BizTalk process requests the information about a policy from the Update service, the Update service first looks for the policy information in its cache. The Update service also checks every 60 seconds (one minute) to see if there have been any updates to the policy in the database. If there are any updates, the Update service retrieves the information and caches the updated information.

There are three tuning parameters for the rule engine related to these caches: CacheEntries, CacheTimeout, and PollingInterval. You can specify the values for these parameters either in the registry or in a configuration file.

The value of CacheEntries is the maximum number of entries in the cache. The default value of CacheEntries is 32. You may want to increase the value of the CacheEntries parameter to improve performance in some cases. For example, suppose you are using 40 policies repeatedly. In this case you may want to increase the value of CacheEntries to 40 to improve performance. This would allow the Update service to cache details of up to 40 policies in memory. It would also cause the BizTalk service to cache up to 40 policy instances in memory. There may be more than one instance of a policy in the cache of the BizTalk service.

The value of CacheTimeout is the time (in seconds) for entries to age out of the Update service cache. In other words, the CacheTimeout value refers to how long a cache entry for a policy is kept in the cache if there are no references to it. The default value of CacheTimeout is 3600 seconds (one hour). This means that, if the cache entry is not referenced within an hour, it is deleted. In some cases, you may want to increase the CacheTimeout value to improve performance. For example, suppose the policy is invoked every two hours. You could improve the performance of the policy execution by increasing the value of the CacheTimeout parameter to a value greater than two hours.

The PollingInterval parameter for the rule engine defines the time in seconds for the interval at which the Update service checks the Rule Engine database for updates. The default value for the PollingInterval parameter is 60 seconds (one minute). If you know that the policies do not get updated at all or are updated rarely, you could increase this value to improve performance.

SideEffects Property

The ClassMemberBinding, DatabaseColumnBinding, and XmlDocumentFieldBinding classes have a property named SideEffects. This property determines whether the value of the bound field, member, or column is cached. The default value of the SideEffects property in the DatabaseColumnBinding and XmlDocumentFieldBinding classes is false. The default value of the SideEffects property in the ClassMemberBinding class is true. Therefore, when a field of an XML document or a column of a database table is accessed for the second time or later within the policy, its value is retrieved from the cache. However, when a member of a .NET object is accessed for the second time or later, the value is retrieved from the .NET object, and not from the cache. Setting the SideEffects property of a .NET ClassMemberBinding to false will improve performance because the value of the field is retrieved from the cache from the second time onwards. You can only do this programmatically. The Business Rule Composer tool does not expose the SideEffects property.

Instances and Selectivity

The XmlDocumentBinding, ClassBinding, and DatabaseBinding classes have two properties: Instances and Selectivity. The value of Instances is the expected number of instances of the class in working memory. The value of Selectivity is the percentage of the class instances that will successfully pass the rule conditions. The rule engine uses these values to optimize the condition evaluation so that the fewest possible instances are used in condition evaluations first and then the remaining instances are used. If you have prior knowledge of the number of instances of the object, setting the Instances property to that value would improve performance. Similarly, if you have prior knowledge of the percentage of these objects passing the conditions, setting the Selectivity property to that value would improve performance. You can only set values for these parameters programmatically. The Business Rule Composer tool does not expose them.