pkey is not used on productive database

Hi,

I need help to understand the issue on a productive database for a select
that takes more time than expected.

1- On a development database I ran the query (select) and I can see on
Explain Analyze pgAdmin use all the indexes and primary keys defined. Dev db
has almost 10% of productive data.

2- On productive database the same query on Explain Analyze from
pgAdmin shows a diferent planning, not using a pkey index and instead uses
the progressive scan on a million of rows. I can see Primary key is defined
for the table on pgAdmin.

What could be the issue on a productive for not use the pkey index for the
SELECT?

Cristian C. Bittel