On 2018-Jun-16, Robert Haas wrote: > I'm not sure that really solves the problem, because changing the GUC > in either direction causes the system to behave differently. I don't > see any particular reason to believe that changing the behavior from A > to B is any more or less likely to break applications than a change > from B to A.
I suppose the other option is to just disallow a change during a running session completely. That is, whatever value is has when you connect is final. Maybe a better idea is to make write-once: the application connects, establishes its desired behavior, and then it cannot be changed anymore. > I put this feature, which - in this interest of full disclosure - is > already implemented in Advanced Server and has been for many years, > more or less in the same category as a hypothetical GUC that changes > case-folding from lower case to upper case. That is, it's really nice > for compatibility, but you can't get around the fact that every bit of > software that is supposed to run on all PostgreSQL instances has to be > tested in all possible modes, because otherwise you might find that it > doesn't work in all of those modes, or doesn't work as expected. It > is a behavior-changing GUC par excellence. Thanks for bringing this up. While I agree that both your example and the feature being proposed are behavior-changing, I don't think the parallel is very good, because the level of effort in order to port from one behavior to the other is much higher with statement-scoped rollback than with case-folding. In the case-folding example, I don't think you need to audit/rewrite all your applications in order to make them work: most of the time just rename a few tables, or if not just add a few quotes (and you can probably do it programatically.) With statement-scope rollback what you face is a more thorough review .. probably adding a savepoint call every other line. I'm not sure that for a large codebase this is even reasonable to start talking about. -- Álvaro Herrera https://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
