Deadlock and aborted queries..

Original sent out under a misleading subject line, I hit reply to get the
list address and forgot to change the subject.  Resent with a real subject.
My apologies.
-----------

Greetings.

I have a smallish sized database that's getting alot of update transactions
to it.  It's been running fine over the past several weeks, but suddenly I'm
starting to see :

NOTICE:  Deadlock detected -- See the lock(l) manual page for a possible cause.
NOTICE:  current transaction is aborted, queries ignored until end of transaction block
NOTICE:  current transaction is aborted, queries ignored until end of transaction block
NOTICE:  current transaction is aborted, queries ignored until end of transaction block
NOTICE:  Deadlock detected -- See the lock(l) manual page for a possible cause.

appear in my apache error logs from my PHP statements.  At the same time the
following messagse appear in Postgres logs :

NOTICE:  Deadlock detected -- See the lock(l) manual page for a possible cause.
ERROR:  WaitOnLock: error on wakeup - Aborting this transaction
DEBUG:  Last error occured while executing PL/pgSQL function add_impression
DEBUG:  line 16 at SQL statement
NOTICE:  current transaction is aborted, queries ignored until end of transaction block
NOTICE:  current transaction is aborted, queries ignored until end of transaction block

This is PostgreSQL 7.0.3 running on a Debian Stable system.  All
transactions to the database are via PHP 4.0.4pl1 under Apache 1.3.17.  I've
made no modifications to the system itself for several weeks (outside of
upgrading apache) and it was running fine under similiar loads in the past.

Any suggestions one how I can rectify this situation would be appriecated.  :)

For reference, the function in question is declared as :

CREATE function add_impression( int4, int4, text ) RETURNS int4 AS '

        DECLARE
                tempvar record;
                linkidx ALIAS FOR $1;
                linkcat ALIAS FOR $2;
                linkloc ALIAS FOR $3;

        BEGIN
                SELECT INTO tempvar *
                FROM linkdaystatsdetail
                WHERE linkid = linkidx
                AND categorynumber = linkcat
                AND location = linkloc;

                IF FOUND THEN
                        UPDATE linkoverviewstatsdetail
                        SET impressions=impressions+1
                        WHERE linkid = linkidx
                        AND categorynumber = linkcat
                        AND location = linkloc;
                ELSE
                        INSERT INTO linkoverviewstatsdetail ( linkid, categorynumber, location, clicks, impressions )
                                VALUES ( linkidx, linkcat, linkloc, 0, 1 );
                END IF;

                UPDATE linkoverviewstats
                SET impressions=impressions+1
                WHERE linkid = linkidx;

                SELECT INTO tempvar *
                FROM linkdaystatsdetail
                WHERE linkid = linkidx
                AND categorynumber = linkcat
                AND location = linkloc;

                IF FOUND THEN
                        UPDATE linkdaystatsdetail
                        SET impressions=impressions+1
                        WHERE linkid = linkidx
                        AND categorynumber = linkcat
                        AND location = linkloc;
                ELSE
                        INSERT INTO linkdaystatsdetail ( linkid, categorynumber, location, clicks, impressions )
                                VALUES ( linkidx, linkcat, linkloc, 0, 1 );
                END IF;

                UPDATE linkdaystats
                SET impressions=impressions+1
                WHERE linkid = linkidx;

                RETURN 1;

        END;
' LANGUAGE 'PLPGSQL';

linkoverviewstatsdetail and linkdaystatsdetail are very similiar in composition, the schema being :

freehost=# \d linkdaystatsdetail
       Table "linkdaystatsdetail"
   Attribute    |    Type    | Modifier
----------------+------------+----------
 linkid         | integer    |
 categorynumber | integer    |
 location       | varchar(1) |
 clicks         | integer    |
 impressions    | integer    |
Indices: linkdaystatsdetail_linkid_idx,
         linkdsd_linkid_cat_loc_idx

freehost=# \d linkdsd_linkid_cat_loc_idx
Index "linkdsd_linkid_cat_loc_idx"
   Attribute    |    Type
----------------+------------
 linkid         | integer
 categorynumber | integer
 location       | varchar(1)
btree

freehost=# \d linkdaystatsdetail_linkid_idx
Index "linkdaystatsdetail_linkid_idx"
 Attribute |  Type
-----------+---------
 linkid    | integer
btree

Thanks in advance,

Sincerely, Warren