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In an ideal world yes, you only manage one database but no such "jack of all trades" DB exists for the same reason the CAP theorem remains true.

If your Postgres JSON schema modified for new application requirements, the table is locked until existing data is copied into the new schema, requiring applications to be quiesced during schema migration.

Thats a key difference between the two and one area Mongo performs best in.

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> If your Postgres JSON schema modified for new application requirements, the table is locked until existing data is copied into the new schema, requiring applications to be quiesced during schema migration.

Are you saying that if you INSERT a row with a new JSONB property that wasn't previously included in any of the rows of that table, then the entire table gets locked while all rows are copied. And if so, do you have a source for that? I can't find anything through google.

Sure there are situations where a Postgres/Mongo hybrid is the best but my preferred default is Postgres only. In most cases this will work fine, is simple and straightforward. Why make things more complicated than necessary?

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