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  1. Documentation
  2. DOCS-13885

Investigate changes in SERVER-48474: Add $sampleRate match expression

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    Details

    • Type: Task
    • Status: Open
    • Priority: Major - P3
    • Resolution: Unresolved
    • Affects Version/s: None
    • Fix Version/s: 4.7.0, 4.4.2
    • Component/s: manual, Server
    • Labels:
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      Description

      Description

      Downstream Change Summary

      We added a new expression, $sampleRate, which lets you select a desired fraction or percentage of documents. (Contrast with $sample, which lets you select a desired number of documents.)

      Description of Linked Ticket

      This match expression takes a floating point number between 0 and 1 (both inclusive) with 0 matching nothing and 1 matching all. It desugars to {$expr: {$rand: ...}}

      Unlike $sample, which is an experession, $sampleRate is a match-expression, which can go inside .find() or {$match: _}.

      For example, the pipeline:

      {$match: {$sampleRate: 0.25}}
      

      Would select on average 1/4 of the input documents. It could desugar to

      {$match: {$expr: {$lt: [ {$rand: {}}, 0.25 ]}}}
      

      Scope of changes

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      Resources (Scope or Design Docs, Invision, etc.)

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              Assignee:
              Unassigned
              Reporter:
              backlog-server-pm Backlog - DB Eng Program Management Team
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              Backlog - DB Eng Program Management Team
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                Dates

                Created:
                Updated:
                Days since reply:
                4 weeks, 5 days ago