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  1. Core Server
  2. SERVER-8187

Usability issues with splitting + hashed shard keys

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    • Type: Icon: Bug Bug
    • Resolution: Done
    • Priority: Icon: Major - P3 Major - P3
    • 2.4.0-rc1
    • Affects Version/s: None
    • Component/s: Sharding
    • Labels:
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    • Fully Compatible
    • ALL
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      5 shards, create a hashed shard key on user_id, populate with 1 million docs of the form

      {user_id:"user"+Math.floor(Math.random()*10000), date:new Date(), something:Math.random()}

      . Try to move a chunk.

      Show
      5 shards, create a hashed shard key on user_id, populate with 1 million docs of the form {user_id:"user"+Math.floor(Math.random()*10000), date:new Date(), something:Math.random()} . Try to move a chunk.

      It seems difficult to split a chunk that is too big to move when using a hashed shard key.

      splitFind claimed to split it, but didn't:

      config> db.chunks.find({shard:"test-rs4"}).count()
12
config> sh.splitFind("test.hashy", {'user_id' : {$gt :  NumberLong("6136905156946055959"), $lt : NumberLong("6376878206583911474")}})
{ "ok" : 1 }
config> db.chunks.find({shard:"test-rs4"}).count()
12

      split+middle gave the fantabulous error message:

      > db.adminCommand({split:"test.hashy", middle:{user_id:NumberLong("6236905156946055959")}})
{
        "cause" : {
                "errmsg" : "exception: can split { user_id: 4525968722311181770 } -> { user_id: 4914820391477438346 } on { user_id: 6236905156946055959 }",
                "code" : 14040,
                "ok" : 0
        },
        "ok" : 0,
        "errmsg" : "split failed"
}

      (NumberLong("6236905156946055959") was chosen randomly, just in case you could pass in a hashed value and have it work).

      It also seems easy to end up in this situation: I randomly populated a collection with 1 million docs and a 1MB chunk chunk size and no chunk I've tried so far has been small enough to move.

            Assignee:
            randolph@mongodb.com Randolph Tan
            Reporter:
            kristina Kristina Chodorow (Inactive)
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              Created:
              Updated:
              Resolved: