SQL question

[Brian Densmore]

Well although this is not Linux related it could easily be.
I have a somewhat large database (approx 180 million records)
that I need to delete certain "sets" from based on a foreign
key in a smaller table (approx 4 million records) and the 
records I want to delete match a field in a third table
(very small < 100 records). I ran this delete query and it ran 
for 18 hours and still didn't finish. We had to kill it
(because the server was swapping back and forth and came 
to a standstill because we only have a 1/2 gig of RAM).
Anyway, I, have two questions:
1) why should it take 18 hours to run (the delete query should
have deleted about 1/3 of the data in the database),
2) is there anyway to have a single delete query statement
do periodic commits (as really dangerous as it is)?

basically what I have is this:

table bad_marks (uid,mark)
table messages  (indice,mark,...)
table msg_elements (id,indice,...)

where bad_marks.mark 1->M/1->0 messages.mark, uid = PK
      messages.indice 1->M msg_element.indice, message.indice = PK, message.mark = indexed
      msg_element id = PK, indice = indexed
and there is no referential integrity turned on (yet).

Thanks,
Brian

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