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  1. Core Server
  2. SERVER-39295

Use readOnce: true for $sample cursors

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Details

    • Improvement
    • Status: Blocked
    • Major - P3
    • Resolution: Unresolved
    • 4.1.7
    • None
    • Aggregation Framework
    • Query Execution
    • Query 2020-03-23

    Description

      This is a feature request to enhance the behaviour of the $sample aggregation command by adding to the plan optimizer the WiredTiger “readOnce: true” option for MongoDB cursors (SERVER-36068).

      The intended purpose behind this enhancement is so $sample does not (or is less likely to) cache the result set.  A sample by definition is unlikely to be used again by subsequent samples, thereby caching has no benefit and only serves to add unwanted cache pressure and workload contention. 

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          depends on

          Task - A task that needs to be done. SERVER-47118 Investigate the behavior of read_once cursors

          • Major - P3 - Major loss of function.
          • Backlog

          Task - A task that needs to be done. SERVER-47055 Investigate performance regression in initial sync collection scan with readOnce cursors

          • Major - P3 - Major loss of function.
          • Closed

          Improvement - An improvement or enhancement to an existing feature or task. SERVER-36068 Expose a user-accessible cursor option to avoid caching data from reads

          • Major - P3 - Major loss of function.
          • Closed

          Activity

            People

              backlog-query-execution Backlog - Query Execution
              luke.prochazka@mongodb.com Luke Prochazka
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              Dates

                Created:
                Updated: