This model couldn't be extended to cover the default collation, and
didn't have any information about the affected database objects when the
version changed. Remove, in preparation for a follow-up commit that
will add a new mechanism.
Author: Thomas Munro <thomas.munro@gmail.com>
Reviewed-by: Julien Rouhaud <rjuju123@gmail.com>
Reviewed-by: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
Discussion: https://postgr.es/m/CAEepm%3D0uEQCpfq_%2BLYFBdArCe4Ot98t1aR4eYiYTe%3DyavQygiQ%40mail.gmail.com
When using collations provided by the ICU library, the ICU-specific version
of the collator is recorded in the system catalog when the collation object
is created. When the collation is used, the current version is
checked against the recorded version, and a warning is issued when there is
a mismatch, for example:
<screen>
WARNING: collation "xx-x-icu" has version mismatch
DETAIL: The collation in the database was created using version 1.2.3.4, but the operating system provides version 2.3.4.5.
HINT: Rebuild all objects affected by this collation and run ALTER COLLATION pg_catalog."xx-x-icu" REFRESH VERSION, or build PostgreSQL with the right library version.
</screen>
A change in collation definitions can lead to corrupt indexes and other
problems because the database system relies on stored objects having a
certain sort order. Generally, this should be avoided, but it can happen
in legitimate circumstances, such as when
using <command>pg_upgrade</command> to upgrade to server binaries linked
with a newer version of ICU. When this happens, all objects depending on
the collation should be rebuilt, for example,
using <command>REINDEX</command>. When that is done, the collation version
can be refreshed using the command <literal>ALTER COLLATION ... REFRESH
VERSION</literal>. This will update the system catalog to record the
current collator version and will make the warning go away. Note that this
does not actually check whether all affected objects have been rebuilt
correctly.
</para>
<para>
When using collations provided by <literal>libc</literal> and
<productname>PostgreSQL</productname> was built with the GNU C library, the
C library's version is used as a collation version. Since collation
definitions typically change only with GNU C library releases, this provides
some defense against corruption, but it is not completely reliable.
</para>
<para>
Currently, there is no version tracking for the database default collation.
</para>
<para>
The following query can be used to identify all collations in the current
database that need to be refreshed and the objects that depend on them:
<programlisting><
Thomas Munro
5 years ago