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A comment on Conformance Checking at MongoDB: Testing That Our Code Matches Our TLA+ Specs. Parent comment

Re:Conformance Checking at MongoDB: Testing That Our Code Ma... by tgv on Tuesday June 03, 2025 @06:51AM (#44168528)
> are there still good reasons for using it in a new project in 2025?

I've written this before: if your data looks like trees, with some loose coupling between them, it's a good choice. And most data does look like trees.

It does place some extra duties on the backend. E.g., mongodb doesn't propagate ("cascade") deletes (this also happens to be a feature I dislike: not so long ago, a delete of an insignificant record triggered an avalanche of deletes in a postgresql database, and restoring that took quite a bit of time.)

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Re:Conformance Checking at MongoDB: Testing That Our Code Ma... by Semaphor on Tuesday June 03, 2025 @09:02AM (#44169565)
Cascading deletes are an optional feature in every DB that supports them, aren’t they? I only have DBA-ish experience with SQL Server, but there they are fully opt in.
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Re:Conformance Checking at MongoDB: Testing That Our Code Ma... by hobs on Tuesday June 03, 2025 @01:55PM (#44172727)
Yes, because they are terrible and break replication for cross system repl.
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Re:Conformance Checking at MongoDB: Testing That Our Code Ma... by Semaphor on Tuesday June 03, 2025 @10:32PM (#44176704)
Yeah, but OP made it seem like they were some kind of mandatory or at least default feature.
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Re:Conformance Checking at MongoDB: Testing That Our Code Ma... by mxey on Tuesday June 03, 2025 @09:08AM (#44169631)
Postgres defaults to preventing delete when foreign keys would be violated, not cascading.
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Re:Conformance Checking at MongoDB: Testing That Our Code Ma... by tgv on Tuesday June 03, 2025 @11:28AM (#44171103)
The sane default. It was a Django project, and unfortunately many relations were set to ondelete=cascade.
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Re:Conformance Checking at MongoDB: Testing That Our Code Ma... by nailer on Tuesday June 03, 2025 @10:06AM (#44170332)
> I've written this before: if your data looks like trees, with some loose coupling between them, it's a good choice. And most data does look like trees.

I had an education statup a little while ago.

Courses had many cohorts, cohorts had many sessions.

It really was much nicer having a single tree structure for each course, appending new cohorts etc, rather than trying to represent this in a flat Postgres database.

That said I acknowledge and agree with other commenter's experiences about MongoDB and data loss in the past.

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Re:Conformance Checking at MongoDB: Testing That Our Code Ma... by elcritch on Tuesday June 03, 2025 @12:10PM (#44171591)
My main concern would be with querying. What is querying like in modern mongodb, or scylladb? I've seen couchbase ads showing a superset of sql, etc. Last I recall Mongo had a weird query system.
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Re:Conformance Checking at MongoDB: Testing That Our Code Ma... by senderista on Tuesday June 03, 2025 @01:21PM (#44172359)
Basically it requires you to write the query plan yourself, which IMO is not a bad idea for an OLTP system.
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