Zero dead tuples, when significant apparent bloat

Here's the situation:

relation_size | indexes_size | total_relation_size
----------------+----------------+---------------------
997 MB | 2073 MB | 3070 MB
(1 row)

If I select n_dead_tup from pg_stat_user_tables, I get:

n_dead_tup
------------
0

Okay, so I run ANALYZE table, then check again:

n_dead_tup
------------
0

Finally, I run VACUUM FULL ANALYZE table. Now I see:

relation_size | indexes_size | total_relation_size
----------------+----------------+---------------------
118 MB | 200 MB | 319 MB
(1 row)

.... ?

It seems clear that there were dead tuples, since the table size shrank to
an eighth of its previous size. Why did analyze not pick that up?

Am I missing something?

This is a very large database, so we want to introspect against live/dead
tuple percentage to minimize the tables we run a VACUUM FULL against.

I've been staring at this for days.

-john

--
John Melesky | Sr Database Administrator
503.284.7581 x204 | john(dot)melesky(at)rentrak(dot)com <vincent(dot)lau(at)rentrakmail(dot)com>
RENTRAK | www.rentrak.com | NASDAQ: RENT

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