<para>

<function>ts_headline</> uses the original document, not a

<type>tsvector</type> summary, so it can be slow and should be used with

care. A typical mistake is to call <function>ts_headline</function> for

<emphasis>every</emphasis> matching document when only ten documents are

to be shown. <acronym>SQL</acronym> subqueries can help; here is an

example:

<programlisting>

SELECT id, ts_headline(body, q), rank

FROM (SELECT id, body, q, ts_rank_cd(ti, q) AS rank

FROM apod, to_tsquery('stars') q

WHERE ti @@ q

ORDER BY rank DESC

LIMIT 10) AS foo;

</programlisting>

care.

</para>

</sect2>