Guesses on what this NestLoop is for?

Folks,

I'm getting this plan on 7.2.4:

----------------------------------------------------------
explain
select events.event_id, events.event_name, type_name,
COALESCE(cases.case_name || '(' || cases.docket || ')',
trial_groups.tgroup_name) as event_case,
jw_date_format(events.event_date, events.event_tz, events.duration) as
show_date
FROM event_types, events
LEFT OUTER JOIN cases ON (events.link_type = 'case' AND events.case_id =
cases.case_id)
LEFT OUTER JOIN trial_groups ON ( events.link_type = 'tg' AND
events.case_id = trial_groups.tgroup_id )
LEFT OUTER JOIN event_history eh ON events.event_id = eh.event_id
WHERE events.status = 1 or events.status = 11
and events.event_date > '2003-10-27'
and events.etype_id = event_types.etype_id
and (
( events.mod_user = 562 AND eh.event_id IS NULL )
OR
( eh.mod_user = 562
and not exists (select 1 from event_history eh2
where eh2.event_id = eh.event_id
and eh2.mod_date < eh.mod_date) )
);

Nested Loop (cost=100004949.08..2676373923.96 rows=3666858 width=197)
-> Hash Join (cost=4949.08..8519.60 rows=43568 width=165)
-> Hash Join (cost=4407.81..6615.02 rows=43568 width=149)
-> Hash Join (cost=4403.21..6485.29 rows=43568 width=125)
-> Seq Scan on events (cost=0.00..1515.70 rows=43568
width=79)
-> Hash (cost=3108.07..3108.07 rows=115355 width=46)
-> Seq Scan on cases (cost=0.00..3108.07
rows=115355 width=46)
-> Hash (cost=4.43..4.43 rows=143 width=24)
-> Seq Scan on trial_groups (cost=0.00..4.43 rows=143
width=24)
-> Hash (cost=524.72..524.72 rows=13240 width=16)
-> Seq Scan on event_history eh (cost=0.00..524.72 rows=13240
width=16)
-> Seq Scan on event_types (cost=0.00..4.32 rows=106 width=32)
SubPlan
-> Seq Scan on event_history eh2 (cost=0.00..557.82 rows=1 width=0)
-----------------------------------------------------------------

What I can't figure out is what is that inredibly expensive nested loop for?
If I could figure that out, maybe I could query around it.

Unfortunately, I can't EXPLAIN ANALYZE because the present query swamps the
machine, and it's a production server. Also it never completes.

And yes, the system is vacuum full analyzed. Event_history is under-indexed,
but the other tables are heavily indexed.

Ideas?

--
-Josh Berkus
Aglio Database Solutions
San Francisco