On 9 September 2016 at 16:21, Magnus Hagander <mag...@hagander.net> wrote: > On Thu, Sep 8, 2016 at 6:19 PM, Peter Eisentraut > <peter.eisentr...@2ndquadrant.com> wrote: >> >> On 9/8/16 11:16 AM, Tom Lane wrote: >> > This is a problem, if ICU won't guarantee cross-version compatibility, >> > because it destroys the argument that moving to ICU would offer us >> > collation behavior stability. >> >> It would offer a significant upgrade over the current situation. >> >> First, it offers stability inside the same version. Whereas glibc might >> change a collation in a minor upgrade, ICU won't do that. And the >> postgres binary is bound to a major version of ICU by the soname (which >> changes with every major release). So this would avoid the situation >> that a simple OS update could break collations. >> >> Second, it offers a way to detect that something has changed. With >> glibc, you don't know anything unless you read the source diffs. With >> ICU, you can compare the collation version before and after and at least >> tell the user that they need to refresh indexes or whatever. >> > > +1 on the importance of this last part. > > We may not be able to handle it directly, but just being able to point out > to the user that "this index is incorrect, you have to reindex" and then > refuse to use the index until that has been done would be a *huge* > improvement. And it would definitely help solve an existing real-world > problem, which is what can happen when you restore a physical backup onto a > different version of an operating system at least. > > Sure, it would be even better if we could automatically *deal* with it. But > failing in a loud and obvious way is a *lot* better than silently returning > incorrect data...
Yep, I strongly agree. That's part of why I think this is well worth doing even though it doesn't look like it'll give us a full solution for stable collations. It's likely also a step or three toward case-insensitive locales/collations, which I'm sure many people would like. Though far from the whole picture. -- Craig Ringer http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
