Full Text Search: Limitations

The current limitations of PostgreSQL's text search features are:

• The length of each lexeme must be less than 2K bytes

• The length of a tsvector (lexemes + positions) must be less than 1 megabyte

• The number of lexemes must be less than 2⁶⁴

• Position values in tsvector must be greater than 0 and no more than 16,383

• The match distance in a <N> (FOLLOWED BY) tsquery operator cannot be more than 16,384

• No more than 256 positions per lexeme

• The number of nodes (lexemes + operators) in a tsquery must be less than 32,768

For comparison, the PostgreSQL 8.1 documentation contained 10,441 unique words, a total of 335,420 words, and the most frequent word "postgresql" was mentioned 6,127 times in 655 documents.

Another example — the PostgreSQL mailing list archives contained 910,989 unique words with 57,491,343 lexemes in 461,020 messages.