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Rethink behavior of pg_import_system_collations().

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Marco Atzeri reported that initdb would fail if "locale -a" reported
the same locale name more than once.  All previous versions of Postgres
implicitly de-duplicated the results of "locale -a", but the rewrite
to move the collation import logic into C had lost that property.
It had also lost the property that locale names matching built-in
collation names were silently ignored.

The simplest way to fix this is to make initdb run the function in
if-not-exists mode, which means that there's no real use-case for
non if-not-exists mode; we might as well just drop the boolean argument
and simplify the function's definition to be "add any collations not
already known".  This change also gets rid of some odd corner cases
caused by the fact that aliases were added in if-not-exists mode even
if the function argument said otherwise.

While at it, adjust the behavior so that pg_import_system_collations()
doesn't spew "collation foo already exists, skipping" messages during a
re-run; that's completely unhelpful, especially since there are often
hundreds of them.  And make it return a count of the number of collations
it did add, which seems like it might be helpful.

Also, re-integrate the previous coding's property that it would make a
deterministic selection of which alias to use if there were conflicting
possibilities.  This would only come into play if "locale -a" reports
multiple equivalent locale names, say "de_DE.utf8" and "de_DE.UTF-8",
but that hardly seems out of the question.

In passing, fix incorrect behavior in pg_import_system_collations()'s
ICU code path: it neglected CommandCounterIncrement, which would result
in failures if ICU returns duplicate names, and it would try to create
comments even if a new collation hadn't been created.

Also, reorder operations in initdb so that the 'ucs_basic' collation
is created before calling pg_import_system_collations() not after.
This prevents a failure if "locale -a" were to report a locale named
that.  There's no reason to think that that ever happens in the wild,
but the old coding would have survived it, so let's be equally robust.

Discussion: https://postgr.es/m/20c74bc3-d6ca-243d-1bbc-12f17fa4fe9a@gmail.com
This commit is contained in:
Tom Lane
2017-06-23 14:19:48 -04:00
parent 9ea3c64124
commit 0b13b2a771
7 changed files with 257 additions and 141 deletions
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24
doc/src/sgml/func.sgml
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@ -19711,9 +19711,9 @@ postgres=# SELECT * FROM pg_walfile_name_offset(pg_stop_backup());
<row>
<entry>
<indexterm><primary>pg_import_system_collations</primary></indexterm>
<literal><function>pg_import_system_collations(<parameter>if_not_exists</> <type>boolean</>, <parameter>schema</> <type>regnamespace</>)</function></literal>
<literal><function>pg_import_system_collations(<parameter>schema</> <type>regnamespace</>)</function></literal>
</entry>
<entry><type>void</type></entry>
<entry><type>integer</type></entry>
<entry>Import operating system collations</entry>
</row>
</tbody>
@ -19730,18 +19730,20 @@ postgres=# SELECT * FROM pg_walfile_name_offset(pg_stop_backup());
</para>
<para>
<function>pg_import_system_collations</> populates the system
catalog <literal>pg_collation</literal> with collations based on all the
locales it finds on the operating system. This is
<function>pg_import_system_collations</> adds collations to the system
catalog <literal>pg_collation</literal> based on all the
locales it finds in the operating system. This is
what <command>initdb</command> uses;
see <xref linkend="collation-managing"> for more details. If additional
locales are installed into the operating system later on, this function
can be run again to add collations for the new locales. In that case, the
parameter <parameter>if_not_exists</parameter> should be set to true to
skip over existing collations. The <parameter>schema</parameter>
parameter would typically be <literal>pg_catalog</literal>, but that is
not a requirement. (Collation objects based on locales that are no longer
present on the operating system are never removed by this function.)
can be run again to add collations for the new locales. Locales that
match existing entries in <literal>pg_collation</literal> will be skipped.
(But collation objects based on locales that are no longer
present in the operating system are not removed by this function.)
The <parameter>schema</parameter> parameter would typically
be <literal>pg_catalog</literal>, but that is not a requirement;
the collations could be installed into some other schema as well.
The function returns the number of new collation objects it created.
</para>
</sect2>