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What this means is that a join using " = " between interval fields would yield different results if implemented as a hash join than if implemented another way , because a large fraction of the pairs that should match will hash to different values and will never be compared by the hash join . Class removal and schema modification Commands that destroy or modify the structure of an existing class , such as alter , drop table , and drop index , only operate for the owner of the class . The other student should hold his or her end of the Slinky still . If the pg_dumpall command seems to take a long time and you think it might have died , then , from another terminal , type $ ls - l db.out several times to see if the size of the file is growing . Once you delete the source files , tar file and regression database , you will need 2 Mbytes for / usr / local / pgsql , 1 Mbyte for the empty database , plus about five times the space you would require to store your database data in a flat file .