PostgreSQL 8.4.7 Documentation
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# 12.11. 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

- 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.

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