Re: Collation versioning

Hello Thomas,

On Tue, May 28, 2019 at 9:00 PM Thomas Munro <thomas(dot)munro(at)gmail(dot)com> wrote:
>
> Since there's a chance of an "unconference" session on locale versions
> tomorrow at PGCon, here's a fresh rebase of the patchset to add
> per-database-object collation version tracking. It doesn't handle
> default collations yet (not hard AFAIK, will try that soon), but it
> does work well enough to demonstrate the generate principal. I won't
> attach the CHECK support just yet, because it needs more work, but the
> point of it was to demonstrate that pg_depend can handle this for all
> kinds of database objects in one standard way, rather than sprinkling
> collation version stuff all over the place in pg_index, pg_constraint,
> etc, and I think it did that already.

Are you planning to continue working on it? For the record, that's
something needed to be able to implement a filter in REINDEX command
[1].

I'm not sending a review since the code isn't finished yet, but one
issue with current approach is that the WARNING message recommending
to issue a REINDEX can be issued when running the required REINDEX,
which is at best unhelpful:

# update pg_depend set refobjversion = 'a' || refobjversion where
refobjversion != '';

# reindex table t1;
WARNING: 01000: index "t1_val_idx" depends on collation 13330 version
"a153.97.35.8", but the current version is "153.97.35.8"
DETAIL: The index may be corrupted due to changes in sort order.
HINT: REINDEX to avoid the risk of corruption.
LOCATION: index_check_collation_version, index.c:1263

[1]: https://www.postgresql.org/message-id/a81069b1-fdaa-ff40-436e-7840bd639ccf%402ndquadrant.com