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  1. Core Server
  2. SERVER-21095

Using tailable cursor on capped collection memory leak

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    • Type: Icon: Bug Bug
    • Resolution: Done
    • Priority: Icon: Major - P3 Major - P3
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    • Affects Version/s: 2.4.7, 3.0.2
    • Component/s: Querying
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      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.

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      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.
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    • 3
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      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.

        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

            Assignee:
            kelsey.schubert@mongodb.com Kelsey Schubert
            Reporter:
            fpf_baden Frank Pfattheicher
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            Watchers:
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              Created:
              Updated:
              Resolved: