Re: SSI patch version 14

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