In PostgreSQL each schema type is stored in its own files with its own index, and every record is accessed separately. In ZODB, a single pickle can include many differetnt classes. Pickles load fast, as a single object access. In contrast. accessing objects with multiple schemas in Postgress requires accessing multiple files. That is slower. In practice, to minimize load times, PostgreSQL developers self-limit the complexity of schemas, making applications more brittle.
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