On Tue, 2011-01-25 at 05:57 -0500, Dan Ports wrote:
> This summary is right on. I would add one additional detail or
> clarification to the last point, which is that rather than checking for
> a cycle, we're checking for a transaction with both "in" and "out"
> conflicts, which every cycle must contain.
To clarify, this means that it will get some false positives, right?
For instance:
T1:
get snapshot
T2:
get snapshot
insert R1
commit
T1:
read R1
write R2
T3:
get snapshot
read R2
T3:
commit
T1:
commit -- throws error
T1 has a conflict out to T2, and T1 has a conflict in from T3.
T2 has a conflict in from T1.
T3 has a conflict out to T1.
T1 is canceled because it has both a conflict in and a conflict out. But
the results are the same as a serial order of execution: T3, T1, T2.
Is there a reason we can't check for a real cycle, which would let T1
succeed?
Regards,
Jeff Davis
--
Sent via pgsql-hackers mailing list ([email protected])
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers
