F.42. tsearch2

F.42.1. Portability Issues

Although the built-in text search features were based on 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 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 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 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.

F.42.2. Converting a pre-8.3 Installation

The recommended way to update a pre-8.3 installation that uses tsearch2 is:

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.

F.42.3. References

Tsearch2 Development Site http://www.sai.msu.su/~megera/postgres/gist/tsearch/V2/