12.11. Limitations

The current limitations of Postgres Pro's text search features are:

  • The length of each lexeme must be less than 2 kilobytes

  • 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.