repoze.pgtextindex

repoze.pgtextindex is an indexing plugin for repoze.catalog that provides a text search engine based on the powerful text indexing capabilities of PostgreSQL 8.4 and above. It is designed to take the place of any text search index based on zope.index. Installation typically requires few or no changes to code that already uses repoze.catalog.

The advantages of repoze.pgtextindex over zope.index.text include:

• Performance. For large datasets, repoze.pgtextindex can be orders of magnitude faster than zope.index, mainly because repoze.pgtextindex does not have the overhead of unpickling objects that zope.index has.
• Lower RAM consumption. Users of zope.index work around the unpickling overhead by keeping large caches of unpickled objects in RAM. Even worse, each thread keeps its own copy of the object cache. PostgreSQL, on the other hand, does not need to maintain complex structures in RAM. The PostgreSQL process size tends to be constant and reasonable.
• Maintenance. The text indexing features of PostgreSQL are well documented and receive a great deal of active maintenance, while zope.index has not received much developer attention for years.

repoze.pgtextindex does not cause PostgreSQL to be involved in every catalog query and update. Only operations that use or change the text index hit PostgreSQL.

Usage

repoze.pgtextindex is used just like any other index in repoze.catalog:

from repoze.pgtextindex import PGTextIndex

index = PGTextIndex(
    discriminator,
    dsn,
    table='pgtextindex',
    ts_config='english',
    drop_and_create=False,
    maxlen=1048575)

The arguments to the constructor are as follows:

discriminator

The repoze.catalog discriminator for this index. For more information on discriminators see the repoze.catalog documentation. This argument is required.

dsn

The connection string for connecting to PostgreSQL. This argument is required.

table

The table to use for the index. The default is 'pgtextindex'.

ts_config

The PostgreSQL text search configuration to use for the index. The default is 'english' which is the default built in configuration which ships with PostgreSQL. For more information on text search configuration, see the PostgreSQL full text search documentation.

drop_and_create

If True the table and index used will dropped (if it exists) and (re)created. The default is False.

maxlen

The maximum number of characters to index per document. The default is 1048575 (2**20 - 1), which is the maximum allowed by the to_tsvector function. Reduce this to improve query speed, since the ts_rank_cd function retrieves and decompresses entire TOAST tuples when querying.