Re: Compatibility GUC for serializable

Tom Lane  wrote:
> I think we've learned over the years that GUCs that significantly
> change semantics can be foot-guns.  I'm not sure exactly how
> dangerous this one would be
I didn't respond to this at first because the idea seemed DOA, but
with Josh's concerns I guess I should answer this question.
With the patch, SERIALIZABLE transactions run exactly as they did
before, and as REPEATABLE READ continue to run, except that they are
monitored for read-write conflict patterns which can cause
serialization anomalies.  This monitoring doesn't introduce any new
blocking.  The only behavior change is that there are additional
serialization failures when the monitoring detects dangerous
structures in the rw-conflicts among transactions.  The proposed GUC
would suppress the monitoring in SERIALIZABLE mode and avoid the new
serialization failures, thereby providing legacy behavior --
anomalies and all.
-Kevin