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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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    • Type: Icon: Bug Bug
    • Resolution: Done
    • Priority: Icon: Major - P3 Major - P3
    • None
    • Affects Version/s: 3.0.6
    • Component/s: WiredTiger
    • None
    • ALL
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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');
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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' );
    • Quint 9 09/18/15, QuInt A (10/12/15)

      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

            Assignee:
            mathias@mongodb.com Mathias Stearn
            Reporter:
            james.wahlin@mongodb.com James Wahlin
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              Created:
              Updated:
              Resolved: