Thanks for the clarification. That explains the time out exceptions and
also makes perfect sense using FOR UPDATE.
On 27/02/2013 10:03 PM, Noel Grandin wrote:
Correct. It's the OPTIMISTIC CONCURRENCY strategy applied to database
modifications.
It looks like this:
while (true) {
generate some changes
if (nothing else has modified the rows we're interested in) {
commit changes
break;
}
throw away changes
if (timed out)
throw exception;
}
If I do FOR UPDATE, it gets an exclusive lock (Table level?), so this
would block readers and writers. But I'm having trouble thinking of a
use case for this.
Sometimes MVCC needs help, or it have trouble making progress on
highly contended rows and tables.
Sessions can find themselves stuck in a retry loop for some time.
In particular, our MVCC implementation is not nearly as smart as
PostgreSQL or Oracle.
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