mongodb impossible (?) E11000 duplicate key error dup key when upserting
I am afraid that this is an ongoing problem. I had the same problem and I found a jira ticket about this: https://jira.mongodb.org/browse/SERVER-14322 It is possible that two updates come in with upsert:true, resulting in neither finding a document and both inserting new documents which conflict on unique index violations of the query predicate. The … Read more