sql - How to speed up deleting documents without rows -

document headers in omdok table:

create table omdok ( dokumnr serial primary key, ... ); 

document rows in omrid table

create table omrid (   id serial not null,   reanr serial not null,   dokumnr integer not null,   constraint omrid_pkey primary key (id),   constraint omrid_dokumnr_fkey foreign key (dokumnr)       references omdok (dokumnr) match simple       on update cascade on delete cascade deferrable immediate,   .... ); 

records in omdok not have child rows in omrid needs deleted

i tried

delete omdok dokumnr not in      (select dokumnr omrid) 

query running 15 hours , still running. postgres.exe using 50% cpu time (this 2 core cpu).

explain delete omdok dokumnr not in      (select dokumnr omrid) 

returns:

"delete  (cost=0.00..21971079433.34 rows=220815 width=6)" "  ->  seq scan on omdok  (cost=0.00..21971079433.34 rows=220815 width=6)" "        filter: (not (subplan 1))" "        subplan 1" "          ->  materialize  (cost=0.00..94756.92 rows=1897261 width=4)" "                ->  seq scan on omrid  (cost=0.00..77858.61 rows=1897261 width=4)" 

• how delete parents without child rows fast?
• will command finish or postgres hanging ?
• currently running 15 hours. how many hours takes finish ? how speed query ?

using

postgresql 9.0.1, compiled visual c++ build 1500, 64-bit  windows 2003 x64 server 4 gb ram. 

another alternative create index on omrid(dokumnr):

create index idx_omrid_dokumnr on omrid(dokumnr); 

this should speed processing of not in in original query.