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  1. Core Server
  2. SERVER-27829

Reduce performance impact of DocumentSourceCursor batching

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    • Query Execution
    • Query 2017-05-29

    Description

      On a large collection with index on "orderdate" compare find and equivalent aggregate first batches:

      command: find { find: "orders", filter: { orderdate: { $gte: new Date(759024000000) } }, sort: { orderdate: -1.0 }, projection: { _id: 0.0, orderdate: 1.0 } } planSummary: IXSCAN { orderdate: 1 } cursorid:53712819499 keysExamined:101 docsExamined:0 numYields:0 nreturned:101 reslen:2903  0ms
      		 
      command: aggregate { aggregate: "orders", pipeline: [ { $match: { orderdate: { $gte: new Date(759024000000) } } }, { $sort: { orderdate: -1.0 } }, { $project: { _id: 0.0, orderdate: 1.0 } } ], cursor: {} } planSummary: IXSCAN { orderdate: 1 } cursorid:52250968997 keysExamined:20972 docsExamined:0 numYields:163 nreturned:101 reslen:2903 11ms

      The main performance difference seems to come from keysExamined which is 101 in case of find and equal to I'm not sure what in the second case (there are 2406 distinct orderdate values, collection size is 1500000 and this filter reduces it to 1034289 documents).

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          is related to

          Improvement - An improvement or enhancement to an existing feature or task. SERVER-47370 Projection pushdown can hinder performance for workloads with tiny documents

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

          Improvement - An improvement or enhancement to an existing feature or task. SERVER-31072 reorder $limit before $lookup in pipeline

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

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              backlog-query-execution Backlog - Query Execution
              asya.kamsky@mongodb.com Asya Kamsky
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