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Fix pg_dump handling of extension config tables

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Since 9.1, we've provided extensions with a way to denote
"configuration" tables- tables created by an extension which the user
may modify.  By marking these as "configuration" tables, the extension
is asking for the data in these tables to be pg_dump'd (tables which
are not marked in this way are assumed to be entirely handled during
CREATE EXTENSION and are not included at all in a pg_dump).

Unfortunately, pg_dump neglected to consider foreign key relationships
between extension configuration tables and therefore could end up
trying to reload the data in an order which would cause FK violations.

This patch teaches pg_dump about these dependencies, so that the data
dumped out is done so in the best order possible.  Note that there's no
way to handle circular dependencies, but those have yet to be seen in
the wild.

The release notes for this should include a caution to users that
existing pg_dump-based backups may be invalid due to this issue.  The
data is all there, but restoring from it will require extracting the
data for the configuration tables and then loading them in the correct
order by hand.

Discussed initially back in bug #6738, more recently brought up by
Gilles Darold, who provided an initial patch which was further reworked
by Michael Paquier.  Further modifications and documentation updates
by me.

Back-patch to 9.1 where we added the concept of extension configuration
tables.
This commit is contained in:
Stephen Frost
2015-03-02 14:12:21 -05:00
parent ee4ddcb38a
commit ebd092bc2a
2 changed files with 88 additions and 1 deletions
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11
doc/src/sgml/extend.sgml
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@ -721,6 +721,17 @@ SELECT pg_catalog.pg_extension_config_dump('my_config', 'WHERE NOT standard_entr
a table as no longer a configuration table is to dissociate it from the
extension with <command>ALTER EXTENSION ... DROP TABLE</>.
</para>
<para>
Note that foreign key relationships between these tables will dictate the
order in which the tables are dumped out by pg_dump. Specifically, pg_dump
will attempt to dump the referenced-by table before the referencing table.
As the foreign key relationships are set up at CREATE EXTENSION time (prior
to data being loaded into the tables) circular dependencies are not
supported. When circular dependencies exist, the data will still be dumped
out but the dump will not be able to be restored directly and user
intervention will be required.
</para>
</sect2>
<sect2>