Application Specific Consistency Control
And finally we get to application specific concurrency control. Historically selling airline tickets had to be perfectly consistent. Two peole could not buy the same seat. Now applications can define their consistency requirements. Even in the airline example, the list of tickets can be slightly out of date, only occasionally will a person go to buy a ticket and fine them all sold out. PostgreSQL is very much based on the computer science notion of perfect consistency. The ZODB mailing list is busy talking about delayed updates to the catalog, after the transaction has completed.
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