question about "delete performance"

I have a table with 500,000 records which has some invalid records, I had wrote a program to check it, by the program I
get all OIDs of the redundant records, so I use "delete from tableXXX where oid =XXX1 or oid =XXX2 or oid =XXX3 ... or
oid=XXX1000, but it take me a long time to complete this action, then I change the query to " delete from tableXXX
whereoid in (XXX1,XXX2,XXX3,....X1000) ", but I got same result, does anyone can tell me the reason or postgresql has a
badperformance in such situation. 

Thanks for help !

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Zhou.daojing on 2005/01/24
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