Re: Q: fixing collation version mismatches - Mailing list pgsql-general

Am Mon, Nov 14, 2022 at 05:42:16PM +0100 schrieb Daniel Verite:

> > Which is why my question still stands: does the above
> > three-strikes operation safely take care of any collation
> > issues that may currently exist in a database ?
>
> For the indexes, yes, but theorically, all constraints involving collatable
> types need a recheck.
>
> For foreign key constraints with non-deterministic collations, there
> might be equality tests that pass with an older Unicode version and fail
> with a newer Unicode version.

Which gives weight to the argument that using real-world data
(instead of surrogate keys) may lead to trouble.

> For check constraints as well, checks applied to strings with recent
> Unicode characters can give different results after an upgrade.

Thanks for pointing this out more clearly. My thinking
already evolved towards also including VALIDATE CONSTRAINT.

I shall, for the record, update the sequence in question:

    -- indices
    REINDEX DATABASE db_in_question;
    -- constraints (check, foreign key)
    UPDATE pg_constraint SET convalidated = false WHERE all_check_and_FK_constraints;
    ALTER TABLE table_with_constraint VALIDATE CONSTRAINT constraint_on_that_table;
    -- other things, see below
    -- ...
    -- refresh collation versions if no errors above
    ALTER DATABASE db_in_question REFRESH COLLATION VERSION;
    ALTER COLLATION every_collation_from_pg_collation REFRESH VERSION;

What else needs to be taken care of, and how ?

partitions

    Need to re-sort rows into the proper partition as needed.

    Can this be achievd by

        UPDATE each_partitioned_table SET each_partitioned_key = each_partitioned_key;

    ?

    Courtesy of (ddl-partitioning.html#DDL-PARTITIONING-CONSTRAINT-EXCLUSION):

        Updating the partition key of a row will cause it to
        be moved into a different partition if it no longer
        satisfies the partition bounds of its original
        partition.

range types

    Will this

        UPDATE table_with_range_type_column SET ranged_column = ranged_column

    find all relevant issues ?

domains

    Will this

        UPDATE table_with_domain_type_column SET domained_column = domained_column

    find all relevant issues ?

custom types

    ??

function immutability ??

    It can be argued that functions marked IMMUTABLE really
    are not in case they involve sorting of a collatable data
    type, and are thus wrongly marked as IMMUTABLE.

    IOW pre-existing user error.

If all this has been discussed in detail, I'd be glad for a
pointer into the archive.

Thanks,
Karsten
--
GPG  40BE 5B0E C98E 1713 AFA6  5BC0 3BEA AC80 7D4F C89B