<row>

<entry><link linkend="catalog-pg-am"><structname>pg_am</structname></link></entry>

<entry>index access methods</entry>

<entry>relation access methods</entry>

</row>

<row>

requests to sample missing or invisible tuples; that should not result in

any bias in the sample. However, if necessary, the function can use

<literal>node-&gt;donetuples</literal> to examine how many of the tuples

it returned werevlaid and visible.

it returned werevalid and visible.

</para>

</note>