Re: Collation versioning

On Fri, Nov 08, 2019 at 02:23:54PM +1300, Thomas Munro wrote:
> Right, so this is basically a policy decision: do we assume that all
> pre-13 indexes that depend on collations are potentially corrupted, or
> assume that they are not? The "correct" thing to do would be to
> assume they are potentially corrupted and complain until the user
> reindexes, but I think the pragmatic thing to do would be to assume
> that they're not and just let them adopt the current versions, even
> though it's a lie. I lean towards the pragmatic choice; we're trying
> to catch future problems, not give the entire user base a load of
> extra work to do on their next pg_upgrade for mostly theoretical
> reasons. (That said, given the new glibc versioning, we'll
> effectively be giving most of our user base a load of extra work to do
> on their next OS upgrade and that'll be a characteristic of PostgreSQL
> going forward, once the versioning-for-default-provider patch goes
> in.) Any other opinions?

Matching an incorrect collation version on an index which physically
uses something else does not strike me as a good idea to me because
you may hide corruptions, and you would actually lose the reason why
the corruption happened (did the version bump up from an incorrect
one? Or what?). Could it be possible to mark any existing indexes
with an unknown version or something like that? This way, we could
just let the user decide what needs to be reindexed or not, and we
need to offer an option to update the collation version from unknown
to the latest one available.
--
Michael