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  1. C Driver
  2. CDRIVER-2736

Mongoc cursor error when running find_with_opts against a sharded cluster

    • Type: Icon: Bug Bug
    • Resolution: Fixed
    • Priority: Icon: Critical - P2 Critical - P2
    • 1.12.0
    • Affects Version/s: 1.5.0
    • Component/s: None
    • None

      The cursor implementation in the mongo-c-driver makes this assumption:

      If the server returns a non-zero cursor id, then the cursor isn't finished because there are more documents to iterate through.

      Right now, sharded clusters return a non-zero cursor id even when the document limit has been reached. So, our cursor throws an error when it gets conflicting information: The user-defined limit has been reached but the cursor id isn't zero.

      Here is the command that fails (all the way back to mongo-c-driver version 1.5):

      mongoc_collection_find_with_opts (
            collection,
            bson_new(), /* filter */
            BCON_NEW("limit", BCON_INT64(2), "batchSize", BCON_INT64(2)), /* other options */
            NULL);
      

      Here is the assertion that fails when the command is ran:

            int64_t remaining = limit - cursor->count;
            BSON_ASSERT (remaining > 0);
      

      I attached an example-client.c file that can be ran to reproduce the bug.

            Assignee:
            jesse@mongodb.com A. Jesse Jiryu Davis
            Reporter:
            spencer.mckenney Spencer Mckenney
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              Created:
              Updated:
              Resolved: