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Comment by aphyr | Hacker News Reader

I like to keep in mind that MongoDB's existing feature set is maturing--occasional regressions may happen, but by and large they're making progress. The problems in this analysis were in a transaction system that's only been around for a couple years, so it's had less time to have rough edges sanded off.

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I’m Dan Pasette, Executive Vice President of Core Engineering at MongoDB. I'd like to thank aphyr for posting the detailed report on MongoDB 4.2.6. We were able to use these findings to identify a bug that can lead to a previously committed transaction being incorrectly retried in the presence of a primary failover and a subsequent transaction commit retry. From our testing, this bug is the cause of the anomalies described in sections 3.4 - 3.7 of the report.

A detailed description of the bug can be found here: https://jira.mongodb.org/browse/SERVER-48307

This bug has been fixed and backported, and will be available to users in MongoDB 4.2.8 onwards. The MongoDB test suite has been updated to ensure that this specific phenomenon is detected in future releases. We are also planning to update the version of Jepsen we are currently running in our CI loop to include the newest test case used in the report.

Last, we’ve made some changes to how we share information discussed in the Jepsen reports on our website. You can find the updated page here (https://www.mongodb.com/jepsen).

there are so many great databases out there. There's no need for one that has been mediocre for years and continues to make false claims. This is an issue of years of super aggressive marketing of an inferior product making it hard on engineers.

I think if you compared it to other databases that are designed to scale horizontally like Cassandra and DynamoDB, you might have a more favorable opinion. IMHO, most products at this scale are terrible in different ways, because it is a difficult problem to solve generally.

I have been responsible for <100 clustered Cassandra instances, and <500 clustered MongoDB instances, and I would choose the latter every time.

Can mongo really support the kind of large scale ETL or time series use cases Cassandra can?

It has been a decade since MongoDB was initially released. It still isn't a database in any meaningful sense of the word. Please don't downplay the amount of trouble one can get into by assuming it is a database.

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