Create a quick-and-dirty list of known migration issues for pre-8.3

users of tsearch.  This isn't meant to be permanent documentation,
but to call out the areas that need either fixing or real documentation.

doc/src/sgml/textsearch.sgml

-<!-- $PostgreSQL: pgsql/doc/src/sgml/textsearch.sgml,v 1.21 2007/10/21 20:04:37 tgl Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/textsearch.sgml,v 1.22 2007/10/22 03:37:04 tgl Exp $ -->
 
 <chapter id="textsearch">
  <title id="textsearch-title">Full Text Search</title>
@@ -3476,9 +3476,98 @@ Parser: "pg_catalog.default"
   <title>Migration from Pre-8.3 Text Search</title>
 
   <para>
-   This needs to be written ...
+   This area needs lots of work.  Here is a quick list of known issues:
   </para>
 
+  <itemizedlist mark="bullet">
+   <listitem>
+    <para>
+     The old contrib/tsearch2 objects <emphasis>must</> be removed from
+     the pg_dump output from a pre-8.3 database.  While many of them won't
+     load for lack of a tsearch2.so library, some do and cause problems.
+     We have a working perl script for doing this with a custom- or tar-format
+     backup, but there is a proposal to incorporate the functionality directly
+     into pg_restore.  Neither approach will help for pg_dumpall output.
+    </para>
+   </listitem>
+
+   <listitem>
+    <para>
+     The old dump may include schema-qualified references to the old
+     contrib/tsearch2 objects; for example <literal>public.tsvector</>
+     columns in table definitions.  These will fail since the objects
+     are now in the pg_catalog schema.  Given current pg_dump behavior
+     this will happen only for tables that are in a different schema
+     from the tsearch2 objects; which makes it more likely to bite
+     people who carefully put their tsearch2 objects in a
+     non-<literal>public</> schema.
+    </para>
+
+    <para>
+     Question: will restore-time failures of this type happen for
+     any objects other than the tsvector and tsquery datatypes?
+    </para>
+
+    <para>
+     The basic alternatives for fixing this seem to involve creating
+     a dummy linkage, such as a public.tsvector domain linking to the
+     base pg_catalog.tsvector type (which only helps for the datatypes);
+     or stripping the schema references out of the dump.  We could
+     just recommend that users do this manually, or try to provide
+     some tools to help.
+    </para>
+   </listitem>
+
+   <listitem>
+    <para>
+     We have renamed the built-in tsvector update triggers, and changed
+     their arguments too.  This will result in CREATE TRIGGER commands
+     failing during load, which can be ignored, but users will need to
+     re-issue them with suitable argument adjustment.  We probably
+     can't automate that for them.  Also, the old tsearch2 trigger
+     function offered an option to invoke functions, which was removed
+     as being a security hole.  Users who were relying on that will need to
+     write custom trigger functions as a substitute.  I think all we
+     can do here is document what to do to fix it.
+    </para>
+   </listitem>
+
+   <listitem>
+    <para>
+     We have renamed a number of other functions besides the triggers,
+     compared to the tsearch2 versions.  This seems unlikely to cause
+     any problems during dump/reload but it will require adjustments in
+     the bodies of stored procedures and in client application code.
+     Again, not much to do except document it.
+    </para>
+   </listitem>
+
+   <listitem>
+    <para>
+     Configuration setup is completely different now.  Can we provide
+     any automated assistance for translating an old custom setup?
+     It probably can't be 100% automatic in any case, so maybe documentation
+     is the best we can do here too.  Aside from the inside-the-database
+     differences, outside-the-database configuration files now have
+     prescribed location and extensions, which was not true before.
+    </para>
+   </listitem>
+
+   <listitem>
+    <para>
+     Relocation of configuration from add-on tables into core system catalogs
+     will break client queries that looked at the add-on tables.
+    </para>
+   </listitem>
+
+   <listitem>
+    <para>
+     What else?
+    </para>
+   </listitem>
+
+  </itemizedlist>
+
  </sect1>
 
 </chapter>