Change the Stop Word Threshold by using Windows PowerShell (FAST Search Server 2010 for SharePoint)

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Applies to: FAST Search Server 2010

The number of matching items used in the rank computation is determined by the StopWordThreshold attribute in the rank profile. If the number of matching items for a search term is larger than the StopWordThreshold for the rank profile being used, the Microsoft FAST Search Server 2010 for SharePoint system automatically retries the search by limiting the managed properties searched. This process is known as drilling. Managed properties are ranked by importance level. Importance level 1, the first level that is used in a search, includes managed properties from levels 1 and up. Drilling to importance level 2 means that only managed properties from levels 2 and up will be used in the search. The maximum importance level is 7.

The value of the StopWordThreshold is relative to a full-text index size of 10,000,000 items. In the default rank profile the StopWordThreshold value is 2,000,000, which means that drilling is performed when a search word is found in more than 20% of items in the full-text index (2,000,000 divided by 10,000,000).

Tip

If you have a small full-text index with a uniform set of items, you might want to increase the StopWordThreshold in order to retrieve rank score from the managed properties in the lower levels (such as body). The performance effect of having a high StopWordThreshold when you have a small full-text index is limited.
To make sure that you get rank from everything, change the StopWordThreshold to 10,000,000. The new StopWordThreshold and the predefined reference number are then equal, which gives a 100% rank calculation at importance level 1.

  1. Verify that you meet the following minimum requirements: You are a member of the FASTSearchAdministrators local group on the computer where FAST Search Server 2010 for SharePoint is installed.

  2. On the Start menu, click All Programs.

  3. Click Microsoft FAST Search Server 2010 for SharePoint.

  4. Click Microsoft FAST Search Server 2010 for SharePoint shell.

  5. At the Windows PowerShell command prompt, type the following command(s):

    $RankProfile = Get-FASTSearchMetadataRankProfile -Name <RankProfile>

    Where:

    • <RankProfile> is the name of the rank profile that you want to change the StopWordThreshold of. The default rank profile is named default.

  6. Look at the current value:

    $RankProfile

>> Name                                   :         default
>> isDefault                              :         False  
>> RankModelName                          :         default
>> StopWordThreshold                      :         2000000
>> PositionStopWordThreshold              :         20000000
>> QualityWeight                          :         50
>> AuthorityWeight                        :         80
>> QueryAuthorityWeight                   :         50
>> FreshnessWeight                        :         100
>> FreshnessResolution                    :         Day
>> FreshnessManagedPropertyReference      :         Write

  7. Change the StopWordThreshold:

    $RankProfile.StopWordThreshold = <StopWordThresholdValue>

    Where:

    • <StopWordThresholdValue> is the value that you want to set the StopWordThreshold to, for example 5000000.

  8. Update the rank profile with the new value:

    $RankProfile.Update()

  9. Look at the rank profile to confirm that the new value is being used:

    $RankProfile

>> Name                                   :         default
>> isDefault                              :         False  
>> RankModelName                          :         default
>> StopWordThreshold                      :         5000000
>> PositionStopWordThreshold              :         20000000
>> QualityWeight                          :         50
>> AuthorityWeight                        :         80
>> QueryAuthorityWeight                   :         50
>> FreshnessWeight                        :         100
>> FreshnessResolution                    :         Day
>> FreshnessManagedPropertyReference      :         Write

See also

RankProfile.StopWordThreshold Property

Importance Level and Drilling

Map a managed property to a full-text index at a specific importance level by using Windows PowerShell (FAST Search Server 2010 for SharePoint)

Set-FASTSearchMetadataRankProfile