ALTER table taking ages...

Greetings!

It takes ages to drop a constraint from one of my tables
[ table details at the end ] I cannot insert into it also.

I know pg_dump is not running and no other query is accessing the table.
Can anyone help me debugging this problem? Can anyone explain the
following entires in pg_locks where relation and database
are both null.

tradein_clients=# SELECT * from pg_locks where mode='ExclusiveLock' and
granted is true;
+----------+----------+-------------+-------+---------------+---------+
| relation | database | transaction | pid | mode | granted |
+----------+----------+-------------+-------+---------------+---------+
| NULL | NULL | 116230313 | 19898 | ExclusiveLock | t |
| NULL | NULL | 116230309 | 24779 | ExclusiveLock | t |
| NULL | NULL | 116230267 | 24780 | ExclusiveLock | t |
| NULL | NULL | 116230303 | 24764 | ExclusiveLock | t |
| NULL | NULL | 116230302 | 24751 | ExclusiveLock | t |
| NULL | NULL | 116230308 | 24767 | ExclusiveLock | t |
| NULL | NULL | 116230274 | 24761 | ExclusiveLock | t |
| NULL | NULL | 116230306 | 24752 | ExclusiveLock | t |
| NULL | NULL | 116230312 | 23222 | ExclusiveLock | t |
| NULL | NULL | 116230290 | 24768 | ExclusiveLock | t |
| NULL | NULL | 116230292 | 24776 | ExclusiveLock | t |
| NULL | NULL | 116230297 | 24753 | ExclusiveLock | t |
| NULL | NULL | 116230295 | 24765 | ExclusiveLock | t |
| NULL | NULL | 116230152 | 24096 | ExclusiveLock | t |
| NULL | NULL | 116230311 | 24769 | ExclusiveLock | t |
| NULL | NULL | 116194826 | 23048 | ExclusiveLock | t |
| NULL | NULL | 116230307 | 24758 | ExclusiveLock | t |
+----------+----------+-------------+-------+---------------+---------+
(17 rows)

Time: 449.422 ms
tradein_clients=# \d general.user_accounts
Table "general.user_accounts"
+-----------------+------------------------+--------------------------------------------------------------------+
| Column | Type |
Modifiers |
+-----------------+------------------------+--------------------------------------------------------------------+
| userid | integer | not null default
nextval('general.user_accounts_userid_seq'::text) |
| username | character varying(50) | not
null |
| password | character varying(50) | not
null |
| title | character varying(15)
| |
| fname | character varying(200)
| |
| mname | character varying(30)
| |
| lname | character varying(30)
| |
| desg | character varying(100)
| |
| creation_date | integer | not
null |
| creation_time | integer | not
null |
| last_visit | integer
| |
| activation_code | double precision
| |
| auto_registered | boolean | not null default
false |
| buy_inquiry | boolean | not null default
true |
| sell_inquiry | boolean | not null default
true |
| webmail_status | character varying(20) | not null default 'NOT
REQUESTED'::character varying |
| account_status | character varying(20) | not null default
'INACTIVE'::character varying |
| section_id | integer | not
null |
| heard_from | integer
| |
+-----------------+------------------------+--------------------------------------------------------------------+
Indexes:
"user_accounts_userid_pkey" primary key, btree (userid)
"user_accounts_index_creation_date" btree (creation_date)
"user_accounts_index_creation_time" btree (creation_time)
"user_accounts_userid" btree (userid)
Check constraints:
"user_accounts_check_account_status" CHECK (account_status::text =
'INACTIVE'::text OR account_status::text = 'ACTIVE'::text OR
account_status::text = 'DISABLED'::text OR account_status::text =
'DELETED'::text)
"user_accounts_check_webmail_status" CHECK (webmail_status::text =
'NOT REQUESTED'::text OR webmail_status::text = 'REQUESTED'::text OR
webmail_status::text = 'ACTIVATED'::text)
Foreign-key constraints:
"user_accounts_fkey_section_id" FOREIGN KEY (section_id) REFERENCES
registration_source(section_id)
"user_accounts_fkey_creation_time" FOREIGN KEY (creation_time)
REFERENCES time_dimension(time_id)
"user_accounts_fkey_creation_date" FOREIGN KEY (creation_date)
REFERENCES date_dimension(date_id)

Regds
Mallah.