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  1. Core Server
  2. SERVER-20385

$sample stage could not find a non-duplicate document while using a random cursor

    Details

    • Backwards Compatibility:
      Fully Compatible
    • Operating System:
      ALL
    • Steps To Reproduce:
      Hide

      Repro'd on Ubuntu 15.04 with a local build of mongod from source.

      Extract tarball to tmp3

      ./mongod --dbpath tmp3 --port 27009
      ./mongo --port 27009
      > use mongodb
      > db.fanclub.aggregate([{$sample: {size: 120}}])
      

      Try the .aggregate query a few times (n < 5)

      Show
      Repro'd on Ubuntu 15.04 with a local build of mongod from source. Extract tarball to tmp3 ./mongod --dbpath tmp3 --port 27009 ./mongo --port 27009 > use mongodb > db.fanclub.aggregate([{$sample: {size: 120}}]) Try the .aggregate query a few times (n < 5)
    • Sprint:
      Quint 9 09/18/15

      Description

      Running 3.1.8-pre (d03334dfa87386feef4b8331f0e183d80495808c)

      > db.fanclub.aggregate([{$sample: {size: 120}}])
      assert: command failed: {
              "ok" : 0,
              "errmsg" : "$sample stage could not find a non-duplicate document after 100 while using a random cursor. This is likely a sporadic failure, please try again.",
              "code" : 28799
      } : aggregate failed
      _getErrorWithCode@src/mongo/shell/utils.js:23:13
      doassert@src/mongo/shell/assert.js:13:14
      assert.commandWorked@src/mongo/shell/assert.js:259:5
      DBCollection.prototype.aggregate@src/mongo/shell/collection.js:1211:5
      @(shell):1:1
      

      It is indeed sporadic in my testing. Should the client ever see this message?

      I am able to reproduce this with --storageEngine=wiredTiger on a somewhat old set of files:

      $ less tmp/WiredTiger
      WiredTiger
      WiredTiger 2.5.1: (December 24, 2014)
      

      However, when I export/import that database into a new --dbpath, I am unable to repro:

      $ less tmp2/WiredTiger
      WiredTiger
      WiredTiger 2.6.2: (June  4, 2015)
      

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                  Updated:
                  Resolved: