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  1. Core Server
  2. SERVER-20197

find() on collection with large documents slower on WiredTiger than MMAPv1

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    Details

    • Type: Bug
    • Status: Closed
    • Priority: Major - P3
    • Resolution: Gone away
    • Affects Version/s: 3.0.6
    • Fix Version/s: None
    • Component/s: WiredTiger
    • Labels:
      None
    • Operating System:
      ALL
    • Steps To Reproduce:
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      1) Setup a 2 member MongoDB 3.0.6 replica set with:

      • One member running WiredTiger
      • One member running MMAPv1

      2) Load a data set with large documents:

      use test;
      var hugeString="";
      for (var i = 0; i < (1024 * 1100); i++) { hugeString = hugeString + "12345"; }
      for (var j = 0; j < 1000; ++j) { db.test.insert({a: hugeString}); }
      

      3) Run the following explain 2 times against both the WiredTiger and the MMAPv1 members:

      use test;
      db.test.find().explain(verbose='executionStats');
      

      Show
      1) Setup a 2 member MongoDB 3.0.6 replica set with: One member running WiredTiger One member running MMAPv1 2) Load a data set with large documents: use test; var hugeString=""; for (var i = 0; i < (1024 * 1100); i++) { hugeString = hugeString + "12345"; } for (var j = 0; j < 1000; ++j) { db.test.insert({a: hugeString}); } 3) Run the following explain 2 times against both the WiredTiger and the MMAPv1 members: use test; db.test.find().explain(verbose='executionStats');
    • Epic Link:
    • Sprint:
      Quint 9 09/18/15, QuInt A (10/12/15)

      Description

      Retrieval of large documents under MongoDB 3.0.6 and WiredTiger is significantly slower than 3.0.6 running MMAPv1. With the following reproduction on my macbook, I saw the following execution times, running the find() operation twice to account for cold data:

      Engine First find Second find
      MMAPv1 312ms 1ms
      WiredTiger 8140ms 668ms

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                • Created:
                  Updated:
                  Resolved: