RE: [Springframework-developer] Petclinic Hibernate implementation

[Trevor C. <pr...@se...>]

<me>
auto-increment just allows to read in the actual id afterwards
This is not reliable for concurrent inserts (which is why I generally =
use sequences)
</me>

<juergen>=20
This is not reliable even with proper transactions? Shouldn't =
"last_insert_id" or whatever it is called return the last inserted id in =
the same transaction, allowing for concurrent inserts in different =
transactions?
</juergen>

With transactions it should function properly.  The problem is that with =
transactions you have different locking strategies which have different =
performance trade-offs depending on the level used.  I've found that =
using identity type fields makes transactions and specific locking =
strategies required.  By using a sequence, I can choose different =
transaction/locking strategies depending on requirements/performance =
(using the identity seems to limit my options).

Also, it's generally a lot harder to change the db (especially the =
primary key) after it's in production.  I can do anything I want with =
sequences, but I have more limited options with identity.  If they work =
today but not tomorrow, it's no longer a simple code change (and getting =
burned by this a few times made me change to sequences as a default).  =
That's just my experience/preference.  As I mentioned though, in this =
case it should work correctly, and since it's a sample app changing the =
db later is perfectly acceptable.  Sorry I took us a little off-topic.

Trevor