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>Chapter 12. Full Text Search</TD
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>12.11. Limitations</A
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><P
> The current limitations of <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>'s
text search features are:
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>The length of each lexeme must be less than 2K bytes</P
></LI
><LI
STYLE="list-style-type: disc"
><P
>The length of a <TT
CLASS="TYPE"
>tsvector</TT
> (lexemes + positions) must be
less than 1 megabyte</P
></LI
><LI
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><P
>The number of lexemes must be less than
2<SUP
>64</SUP
></P
></LI
><LI
STYLE="list-style-type: disc"
><P
>Position values in <TT
CLASS="TYPE"
>tsvector</TT
> must be greater than 0 and
no more than 16,383</P
></LI
><LI
STYLE="list-style-type: disc"
><P
>No more than 256 positions per lexeme</P
></LI
><LI
STYLE="list-style-type: disc"
><P
>The number of nodes (lexemes + operators) in a <TT
CLASS="TYPE"
>tsquery</TT
>
must be less than 32,768</P
></LI
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><P>
</P
><P
> For comparison, the <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> 8.1 documentation
contained 10,441 unique words, a total of 335,420 words, and the most
frequent word <SPAN
CLASS="QUOTE"
>"postgresql"</SPAN
> was mentioned 6,127 times in 655
documents.
</P
><P
> Another example — the <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> mailing
list archives contained 910,989 unique words with 57,491,343 lexemes in
461,020 messages.
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