Does changing the order of elements affect -Filter performance?

Question

Say I am querying Active Directory with Get-ADUser -Filter "ObjectClass -eq 'user' -and 'Name -like '*foo*'".

Does reversing the order of ObjectClass and Name change the order of the query passed to Active Directory and thus affect performance? According to this StackOverflow post, PowerShell converts the -Filter into an LDAP query before being passed to the server.

Assuming it does, in what order is the statement evaluated? Left to right, or something else?

Answer 1

Some high-level pointers:

• It's fair to assume that evaluation is left to right (I have no source to back that up), but whether the translation of the PowerShell-like -Filter expression into an LDAP query behind the scenes even preserves that order is not obvious, judging by the juxtaposition of -Filter arguments and corresponding LDAP queries in the Filter Examples section of the conceptual about_Active_Directory_Filter help topic: the subexpression order in the -Filter isn't consistently preserved there - though that could just be an inaccuracy in the documentation.

• Generally speaking, given that an -and operation is short-circuiting, you'll get better performance if you place the test that executes more quickly on the LHS:

  • This ensures that the comparatively slower test needn't be executed if the quicker one is negative.

  • At least hypothetically, in the case at hand ObjectClass -eq 'user' could be quicker, given that wildcard matching (-like) is more complex than equality comparison
    (-eq).

    • However, both -eq and -like translate into the same operator on the LDAP side, =; see the Supported Operators in the linked help topic for details.

    • Either way, it may not make much difference in practice in this case.

• The linked help topic also has an Optimizing Filters section, excerpted here:

  You can enhance the search filter behavior by using these guidelines.

  • Avoid using the Recursive parameter as it intensifies resource usage of the search operation.

  • Avoid using bitwise AND operators and bitwise OR operators. For more information, see the Supported Operators section of this topic.

  • Avoid using the logical NOT operator.

  • Break down your search into multiple queries with narrower conditions.