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Re: Search speed regarding BDB_IDL_LOGN and order in search filter

Meike Stone wrote:

Hello,

I'm sorry, but I want to ask again for clarifying.

First question:

- An index slot is loosing precision if the search result for an
(indexed) attribute is larger than 2^16. Then the search time is going
to increase a lot.
- I can change this via BDB_IDL_LOGN.
- But if I have a directory, that holds 200.000 employees with
'(ObjectClass=Employees)', the result is larger than 2^16 and it is
slow.
- lets say, the employees are distributed over 4 continents and the
DIT is structured geographical eg.:

      o=myOrg, c=us (100,000 employees)
      o=myOrg, c=gb ( 30,000  employees)
      o=myOrg, c=de ( 25,000 employees)
      o=myOrg, c=br  ( 45,000 employees)

Can i prevent it this problem with index slot size, if I change the
search base to "o=myOrg, c=gb", because there are only 30,000
employees.


Try it and see.
If you're already playing with low-level definitions in the source code, you have no need for us to answer these questions. Or, if you need us to answer these questions, you have no business playing with low-level definitions in the source code. 


This takes me to the second question:

"How is a search filter evaluated?"

Lets say, I combine  three filter via "and" like
'(&(objectlass=Employees)(age=30)(sex=m))' and the all attributes are
indexed. Each filter results:
(objectlass=Employees) => 200,000 entries
(age=30)  => 10,000 entries
(sex=m)    => 3,000 entries

Does the order matter regarding speed, is it better to form the filter
like this?
  '(&(sex=m)(age=30)(objectlass=Employees))'


Try it and see.
If you have advance knowledge of the characteristics of your data, perhaps you can optimize the filter order. In most cases, your applications will not have such knowledge, or it will be irrelevant. For example, if you have a filter term that matches zero entries, it is beneficial to evaluate that first in an AND clause. But it would make no difference in an OR clause. 

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