While a transaction is obviously safer, with the number of tables
and rows referencing these tables now, a transaction is potentially
locking up a significant chunk of the database. Since we're already
performing cleanup before calling the delete, including disabling
new data being written for the User or Repository, deletion without
a transaction should (usually) be sufficient; if it isn't, an
IntegrityError will be raised, and the workers can retry continuing
the GC operation
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