More buffers used than a relation's relpages

Hello,

In what cases can a relation use more buffers (in shared memory) than
its pg_class.relpages?

For example, look at the second row in the following:

postgres=# SELECT c.relname,count(*) AS buffers, c.relpages
FROM pg_class c INNER JOIN pg_buffercache b
ON b.relfilenode=c.relfilenode INNER JOIN pg_database d
ON (b.reldatabase=d.oid AND d.datname=current_database())
GROUP BY c.relname,c.relpages
ORDER BY 2 DESC;
relname | buffers | relpages
-----------------------------------+---------+----------
abc_idx | 4800 | 4800
abc | 3548 | 3547
abc_2_idx | 3209 | 3209
...
...

--
Amit Langote