Limitation on number of positions (tsearch)

Why is there a limitation of 256 positions per lexeme in a tsvector?
There doesn't seem to be a technical reason for that. WordEntryPosVector
uses a uint16 to store the number of positions, so it go up to 65535.

For two reasons:
- Ranking might become very slow if number of position is big
- From practice: if word is very frequent on document then with high probability
this is a stop word or (case of internet-wide search engines) document is a spam.

That's common practice of search engines to limit number of word's positions,
because increasing it doesn't give advantage in term of ranking
and cause trouble from increasing of storage size.
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Teodor Sigaev E-mail: teodor@sigaev.ru
WWW: http://www.sigaev.ru/