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  1. Core Server
  2. SERVER-21095

Using tailable cursor on capped collection memory leak

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    Details

    • Type: Bug
    • Status: Closed
    • Priority: Major - P3
    • Resolution: Gone away
    • Affects Version/s: 2.4.7, 3.0.2
    • Fix Version/s: None
    • Component/s: Querying
    • Labels:
      None
    • Operating System:
      ALL
    • Steps To Reproduce:
      Hide

      Create capped collection.
      Insert one record - save id,
      Create tailable cursor with query id > saved id.
      tyr to get next record in a loop.
      Every loop ther is an amount of memory leaked in the server.

      Show
      Create capped collection. Insert one record - save id, Create tailable cursor with query id > saved id. tyr to get next record in a loop. Every loop ther is an amount of memory leaked in the server.

      Description

      Using a tailable cursor on a capped collection leads to memory leak in the server if the first cursor MoveNext does not get a record.

      BsonValue lastId = collection.FindAll().SetSortOrder(SortBy.Descending("_id")).SetLimit(1).First()["_id"];
       
      cursor = collection.Find(Query.GT("_id", lastId))
                    .SetFlags(QueryFlags.AwaitData | QueryFlags.TailableCursor | QueryFlags.NoCursorTimeout);
       
      using (var enumerator = new MongoCursorEnumerator<BsonDocument>(cursor))
      {
      	while (triggerThread.IsAlive)
      	{
      		if (enumerator.MoveNext())
      		{
      			var document = enumerator.Current;
      			if (document != null)
      			{
      				HandleNextData(document);
      			}
      		}
      		else
      		{
      			if (enumerator.IsDead)
      			{
      				break;
      			}
      			if (!enumerator.IsServerAwaitCapable)
      			{
      				Thread.Sleep(TimeSpan.FromMilliseconds(100));
      			}
      		}
      	}
      }
      

      If the cursor query is changed to "GTE"

      cursor = collection.Find(Query.GTE("_id", lastId))
      

      so as the first result the last record is returned all works fine.

        Attachments

        1. IncreasingOpenCursors.png
          IncreasingOpenCursors.png
          81 kB
        2. metrics.2016-04-04T07-28-52Z-00000
          39 kB
        3. mongod-21095.log
          31.39 MB
        4. screenshot.png
          screenshot.png
          19 kB
        5. TailableCursorLegacy.zip
          967 kB

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              Dates

              • Created:
                Updated:
                Resolved: