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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.

Comments


July 5, 2011, 8:56 p.m.

The 1 megabyte tsvector limitation is based on the number of unique words, not the length of the text. It will not exceeded by typical large books, but will be exceeded many times over by a dictionary due to the number of unique words.

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