[Plugin: Google XML Sitemaps] Very heavy query if selected Include following pages of multi-page pos

If I select Include following pages of multi-page posts (<!–nextpage–>)
I get horrible slow query like this:

# Query_time: 27 Lock_time: 0 Rows_sent: 2527 Rows_examined: 5594
SELECT ID, post_author, post_date, post_date_gmt, post_status, post_name, post_modified, post_modified_gmt, post_parent, post_type , (character_length(post_content) – character_length(REPLACE(post_content, ‘<!–nextpage–>’, ”))) / 15 as postPages FROM wp_posts WHERE ((post_status = ‘publish’ AND post_date_gmt <= ‘2008-11-03 08:56:59′) OR post_status=’static’ ) AND post_password=” ORDER BY post_modified DESC;
# Time: 081103 9:59:56

I think that the count of the pages should be different, and use the fulltext indexes to find ids of posts that should have multiple pages like this:

select ID from wp_posts where match(post_name , post_content ) against (‘nextpage’)

before counting pages with that expensive query.