Improving the performance of the export
作者：佚名
The export utility (exp) can table a long time to export a database. At
our site it takes 8 hours to perform a full export.
The quickest and easiest way to improve the performance of any export
is to use the keyword direct = "Y" with your exports. This will
then cause the export to bypass the buffer cache while performing an export,
creating a significant performance gain
Improving the usability of the export
Did you know that the export process exports each table in turn. The Oracle
database ensures that the export of each table occurs in a read consistent
state. But the moment that the export has completed the export of Table
A and moved onto the export of Table B any number of transactions can
occur on Table A.
But whats the problem with that?, you may ask.
If table A and Table B are related by Foreign Keys then the export may
no longer be in a consistent state if you attempt to import it at a later
time. To correct this problem you can either perform your exports when
there is no activity of the database (not a good idea) or use the keyword
consistent = "Y". This will force the export to produce a read
consistent export of the database. This keyword only works with a full
export. Using this options affects the performance of the export because
a rollback segment is used to track all the changes made to the database
while the export is progressing.
