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When creating a uniqueness constraint using a pre-existing index, we have always required that the index have the same properties you'd get if you just let a new index get built. However, when collations were added, we forgot to add the index's collation to that check. It's hard to trip over this without intentionally trying to break it: you'd have to explicitly specify a different collation in CREATE INDEX, then convert it to a pkey or unique constraint. Still, if you did that, pg_dump would emit a script that fails to reproduce the index's collation. The main practical problem is that after a pg_upgrade the index would be corrupt, because its actual physical order wouldn't match what pg_index says. A more theoretical issue, which is new as of v12, is that if you create the index with a nondeterministic collation then it wouldn't be enforcing the normal notion of uniqueness, causing the constraint to mean something different from a normally-created constraint. To fix, just add collation to the conditions checked for index acceptability in ADD PRIMARY KEY/UNIQUE USING INDEX. We won't try to clean up after anybody who's already created such a situation; it seems improbable enough to not be worth the effort involved. (If you do get into trouble, a REINDEX should be enough to fix it.) In principle this is a long-standing bug, but I chose not to back-patch --- the odds of causing trouble seem about as great as the odds of preventing it, and both risks are very low anyway. Per report from Alexey Bashtanov, though this is not his preferred fix. Discussion: https://postgr.es/m/b05ce36a-cefb-ca5e-b386-a400535b1c0b@imap.cc |
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PostgreSQL Database Management System ===================================== This directory contains the source code distribution of the PostgreSQL database management system. PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings. PostgreSQL has many language interfaces, many of which are listed here: https://www.postgresql.org/download See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.