Planet NoSQL

[Reposted from my article: http://blog.couchbase.com/2016/july/testing-mongodb-and-couchbase-concurrent-query  and https://dzone.com/articles/concurrency-behavior-mongodb-vs-couchbase ] Multi-User Testing David Glasser of Meteor wrote a blog on an MongoDB query missing matching documents issue he ran into.  It is straightforward to reproduce the issue on both MongoDB MMAPv1 and MongoDB WiredTiger engine. Here are his conclusions from his article (emphasis is mine) Long story short… This issue doesn’t affect queries that don’t use an index, such as queries that just look up a document by ID. It doesn’t affect queries which explicitly do a single value equality match on all fields used in the index key. It doesn’t affect queries that use indexes whose fields are never modified after the document is originally inserted. But any other kind of MongoDB query can fail to include all the matching documents! Here’s another way to look at it. In MongoDB...