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Well, I've never used postgres, but from the documentation v9.4 it does not look that different from the others db engine: 'Read Committed is the default isolat

by nkeywal 12y ago

Well, I've never used postgres, but from the documentation v9.4 it does not look that different from the others db engine: 'Read Committed is the default isolation'; 'applications using this level must be prepared to retry transactions due to serialization failures' (plus the one you mentioned already: 'Serializable transaction isolation level has not yet been added to Hot Standby replication targets') Not exactly what I like to call 'simply works' ;-) But I didn't want to say that a NoSQL database is always better than an traditional one. Just that Isolation is complex on traditional systems when dealing with volumes & concurrency. And, typically, transactions between tables or even rows are difficult/impossible for a distributed database, as these rows can be on different nodes (the 'multi-key operations' you mentioned)

AlisdairO 12y ago
Postgres is quite different in one respect: it has a truly serializable snapshot isolation, at an acceptable performance cost (single digit percentage generally). Other DB systems are either not truly serializable, or have lock-based systems that are sometimes more difficult to work with for web apps. > 'applications using this level must be prepared to retry transactions due to serialization failures' True of any serializable system that supports concurrent access, AFAIK - not quite sure that's a fair criticism :-). ------ > And, typically, transactions between tables or even rows are difficult/impossible for a distributed database Depends what you mean by 'distributed', really - Oracle RAC is very much distributed, and supports normal transactional behaviour. On the other hand you won't get that working across a large geographical area. I accept that understanding the impact of isolation levels can be complex - I'm just very much of the opinion that you'll take a lot more pain trying to maintain consistency in a typical NoSQL system.
- nkeywal 12y ago
  I can agree with these facts. I just give them a different weight than you do: I don't like the incertitude of the 'serialization failures': it depends on a workload that can be difficult to predict, especially if you're a software vendor. YMMV :-) Thanks for the constructive feedback.
  - AlisdairO 12y ago
    Thanks for a good read/conversation!

by nkeywal 12y ago

AlisdairO 12y ago

Postgres is quite different in one respect: it has a truly serializable snapshot isolation, at an acceptable performance cost (single digit percentage generally). Other DB systems are either not truly serializable, or have lock-based systems that are sometimes more difficult to work with for web apps. > 'applications using this level must be prepared to retry transactions due to serialization failures' True of any serializable system that supports concurrent access, AFAIK - not quite sure that's a fair criticism :-). ------ > And, typically, transactions between tables or even rows are difficult/impossible for a distributed database Depends what you mean by 'distributed', really - Oracle RAC is very much distributed, and supports normal transactional behaviour. On the other hand you won't get that working across a large geographical area. I accept that understanding the impact of isolation levels can be complex - I'm just very much of the opinion that you'll take a lot more pain trying to maintain consistency in a typical NoSQL system.

nkeywal 12y ago
I can agree with these facts. I just give them a different weight than you do: I don't like the incertitude of the 'serialization failures': it depends on a workload that can be difficult to predict, especially if you're a software vendor. YMMV :-) Thanks for the constructive feedback.
- AlisdairO 12y ago
  Thanks for a good read/conversation!