delete commands fails silently to delete primary key

["Andrus" <kobruleht2@xxxxxx>]

I have table in 8.1.4 which tracks users logged into db

CREATE TABLE "session"
(
 workplace character(16) NOT NULL,
 ipaddress character(20),
 logintime character(28),
 loggeduser character(10),
 CONSTRAINT session_pkey PRIMARY KEY (workplace)
);

Commands executed at logon in same transaction are:

delete from session where workplace=E'LIIVA' ;
insert into session (workplace,ipaddress,logintime,loggeduser) values ( 
E'LIIVA' , inet_client_addr()::CHAR(14), 
current_timestamp::CHAR(28),CURRENT_USER)

Sometimes (during locking contention or during heavy load) those commands 
cause error:

2008-11-22 11:24:26 EET INSERT 1 47433335ERROR:  duplicate key violates 
unique constraint "session_pkey"
2008-11-22 11:24:26 EET INSERT 2 47433335STATEMENT:  delete from session 
where workplace=E'LIIVA' ;insert into session 
(workplace,ipaddress,logintime,loggeduser) values (  E'LIIVA' , 
inet_client_addr()::CHAR(14), current_timestamp::CHAR(28),CURRENT_USER)

No other client can add 'LIIVA' primary key.
Any idea why this error occurs and how to fix ?

Andrus.


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