Need some help with crafting a query to do major update

To all,

This is part of a data warehouse. Made the mistake of using a natural
key in one of the fact tables. :-( The f_test_pageviews is a simple
testing table while I work this out. The real table has an identical
schema.

I have built a mapping table, d_user, to allow the replacement of the
text based (32 characters wide) subscriber_key in f_test_pageviews with
an int4 mapping key. I need to replace all of the
f_test_pageviews.subscriber_key values with the d_user.id value putting
it in f_test_pageviews.sub_key column.

I have tried this sql:

update f_test_pageviews set sub_key = t2.id from f_test_pageviews t1,
d_user t2 where t1.subscriber_key = t2.user_id;

but it is taking forever to complete. I would appreciate it if anyone
could tell me a faster way to do this. I have to update 250 million
plus rows over 4 tables. (We break the page view tables into calendar
months)

Thanks.

--sean

Table "public.d_user"
Column | Type | Modifiers
---------+---------+--------------------------------------------------------
id | integer | not null default nextval('public.d_user_id_seq'::text)
user_id | text | not null
Indexes:
"d_user_pkey" primary key, btree (id)
"d_user_user_id_key" unique, btree (user_id)

Table "public.f_test_pageviews"
Column | Type | Modifiers
------------------------+---------+-----------
id | integer |
date_key | integer |
time_key | integer |
content_key | integer |
location_key | integer |
session_key | integer |
subscriber_key | text |
persistent_cookie_key | integer |
ip_key | integer |
referral_key | integer |
servlet_key | integer |
tracking_key | integer |
provider_key | text |
marketing_campaign_key | integer |
orig_airport | text |
dest_airport | text |
commerce_page | boolean |
job_control_number | integer |
sequenceid | integer |
url_key | integer |
useragent_key | integer |
web_server_name | text |
cpc | integer |
referring_servlet_key | integer |
first_page_key | integer |
newsletterid_key | text |
sub_key | integer |
Indexes:
"idx_temp_pageviews_id" unique, btree (id)