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Editorial Team
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Asked: 2026-05-18T23:50:13+00:00

I’m seeing a ton of these errors An existing connection was forcibly closed by

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I’m seeing a ton of these errors

“An existing connection was forcibly closed by the remote host”

in the Mongo log since I switched from the open source c# driver to the 10Gen supported one. Once this error happens my websites become unresponsive. I have a feeling it has something to do with the way connection pooling is implemented. See log below, I’m deleting indexes from a collection, removing all items, then ‘recreating’ the collection by adding all the rows I want and then re indexing the collection. A few moments after that is all done I invariably get the error : ‘An existing connection was forcibly closed by the remote host’

[conn46] run command admin.$cmd { ismaster: 1 }
[conn46] query admin.$cmd ntoreturn:1 command: { ismaster: 1 } reslen:64 0ms
[conn46] query BtSearchCache.system.indexes reslen:1407 nreturned:7 0ms

drop indexes
[conn46] run command BtSearchCache.$cmd { deleteIndexes: "Board_41", index: "ix_QuickSearch" }
[conn46] CMD: dropIndexes BtSearchCache.Board_41
[conn46] dropIndexes: ix_QuickSearch not found
[conn46] query BtSearchCache.$cmd ntoreturn:1 command: { deleteIndexes: "Board_41", index: "ix_QuickSearch" } reslen:81 1ms

remove all data from collection
[conn46] remove  query: {} 1428ms

insert data (thousands of rows, omitted here)

[conn46] insert BtSearchCache.Board_41 0ms
[conn46] insert BtSearchCache.Board_41 0ms
[conn46] insert BtSearchCache.Board_41 1ms
[conn46] insert BtSearchCache.Board_41 0ms
[conn46] insert BtSearchCache.system.indexes 0ms

create indexes
[conn46] run command admin.$cmd { getlasterror: 1 }
[conn46] query admin.$cmd ntoreturn:1 command: { getlasterror: 1 } reslen:65 0ms

ERROR a few minutes later
[conn46] MessagingPort recv() errno:10054 An existing connection was forcibly closed by the remote host. 192.168.100.216:51111
[conn46] SocketException: 9001 socket exception
[conn46] end connection 192.168.100.216:51111
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1 Answer

  1. Editorial Team

    Followup: this question was also asked in the mongodb-user group on Google and most of the discussion happened there. In the end what we found out was that a particular query was causing the mongo server to crash (the bug is already fixed in current versions of the server) and the C# driver was simply reporting the connection failures that resulted. This was not a bug in the C# driver and no fix was required to the driver. The C# driver would reconnect once the server was brought back up.

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