Tom's recent changes to allow hash distinct (yay!) prompted something
that I'd thought about previously.
Subtle changes in the output of queries can force an application retest,
which then can slow down or prevent an upgrade to the latest release. We
always assume the upgrade itself is the problem, but the biggest barrier
I see is the cost and delay involved in upgrading the application.
We could invent a new parameter called enable_sort_distinct, but thats
way too specific and horrible.
What I would like is a parameter called sql_compatibility which has
settings such as 8.3, 8.4 etc.. By default it would have the value 8.4,
but for people that want to upgrade *without* retesting their
application, they could set it to 8.3.
Every time we introduce a feature that changes output, we just put an if
test in saying sql_compatibility = X, (the release we added feature).
Straightforward, futureproof. Cool.
Not foolproof, but still worth it. This would allow many users to
upgrade to 8.4 for new features, yet without changing apps.
-- Simon Riggs www.2ndQuadrant.comPostgreSQL Training, Services and Support
