--- /dev/null
+
+
tsearch2
+
+
+
+
+ The tsearch2 module provides backwards-compatible
+ text search functionality for applications that used
+ contrib/tsearch2 before text searching was integrated
+ into core
PostgreSQL in release 8.3.
+
+
+
+
Portability Issues
+
+ Although the built-in text search features were based on
+ contrib/tsearch2 and are largely similar to it,
+ there are numerous small differences that will create portability
+ issues for existing applications:
+
+
+
+
+ Some functions' names were changed, for example rank
+ to ts_rank.
+ The replacement tsearch2 module
+ provides aliases having the old names.
+
+
+
+
+ The built-in text search data types and functions all exist within
+ the system schema pg_catalog. In an installation using
+ contrib/tsearch2, these objects would usually have been in
+ the public schema, though some users chose to place them
+ in a separate schema of their own. Explicitly schema-qualified
+ references to the objects will therefore fail in either case.
+ The replacement tsearch2 module
+ provides alias objects that are stored in public
+ (or another schema if necessary) so that such references will still work.
+
+
+
+
+ There is no concept of a current parser or current
+ dictionary in the built-in text search features, only of a current
+ search configuration (set by the default_text_search_config
+ parameter). While the current parser and current dictionary were used
+ only by functions intended for debugging, this might still pose
+ a porting obstacle in some cases.
+ The replacement tsearch2 module emulates these
+ additional state variables and provides backwards-compatible functions
+ for setting and retrieving them.
+
+
+
+
+ There are some issues that are not addressed by the replacement
+ tsearch2 module, and will therefore require
+ application code changes in any case:
+
+
+
+
+ The old tsearch2 trigger function allowed items in its
+ argument list to be names of functions to be invoked on the text data
+ before it was converted to tsvector format. This was removed
+ as being a security hole, since it was not possible to guarantee that
+ the function invoked was the one intended. The recommended approach
+ if the data must be massaged before being indexed is to write a custom
+ trigger that does the work for itself.
+
+
+
+
+ Text search configuration information has been moved into core
+ system catalogs that are noticeably different from the tables used
+ by contrib/tsearch2. Any applications that examined
+ or modified those tables will need adjustment.
+
+
+
+
+ If an application used any custom text search configurations,
+ those will need to be set up in the core
+ catalogs using the new text search configuration SQL commands.
+ The replacement tsearch2 module offers a little
+ bit of support for this by making it possible to load an old set
+ of contrib/tsearch2 configuration tables into
+
PostgreSQL 8.3. (Without the module,
+ it is not possible to load the configuration data because values in the
+ regprocedure columns cannot be resolved to functions.)
+ While those configuration tables won't actually do
+ anything, at least their contents will be available to be consulted
+ while setting up an equivalent custom configuration in 8.3.
+
+
+
+
+ The old reset_tsearch() and get_covers()
+ functions are not supported.
+
+
+
+
+ The replacement tsearch2 module does not define
+ any alias operators, relying entirely on the built-in ones.
+ This would only pose an issue if an application used explicitly
+ schema-qualified operator names, which is very uncommon.
+
+
+
+
+
+
+
+
Converting a pre-8.3 Installation
+
+ The recommended way to update a pre-8.3 installation that uses
+ contrib/tsearch2 is:
+
+
+
+ Make a dump from the old installation in the usual way,
+ but be sure not to use -c (--clean)
+ option of
pg_dump or pg_dumpall.+
+
+
+
+ In the new installation, create empty database(s) and install
+ the replacement tsearch2 module into each
+ database that will use text search. This must be done
+ before loading the dump data! If your old installation
+ had the contrib/tsearch2 objects in a schema other
+ than public, be sure to adjust the
+ tsearch2 installation script so that the replacement
+ objects are created in that same schema.
+
+
+
+
+ Load the dump data. There will be quite a few errors reported
+ due to failure to recreate the original contrib/tsearch2
+ objects. These errors can be ignored, but this means you cannot
+ restore the dump in a single transaction (eg, you cannot use
+
pg_restore's -1 switch).+
+
+
+
+ Examine the contents of the restored contrib/tsearch2
+ configuration tables (pg_ts_cfg and so on), and
+ create equivalent built-in text search configurations as needed.
+ You may drop the old configuration tables once you've extracted
+ all the useful information from them.
+
+
+
+
+ Test your application.
+
+
+
+
+ At a later time you may wish to rename application references
+ to the alias text search objects, so that you can eventually
+ uninstall the replacement tsearch2 module.
+
+
+
+
+
+
References
+ Tsearch2 Development Site
+
+
+
+
projects / postgresql.git / commitdiff