Databases Reference
In-Depth Information
Once the backup is taken, the current table is dropped. When the import takes place
it rebuilds the table with the data, as it was before. The import parameter file has
been temporarily modified so it defines the log file name, and it includes only the
minimum required parameters for the
impdp
task (
C
).
USERID=hr/hr
DIRECTORY=default_dp_dest
DUMPFILE=hrExpAtRestorePoint
JOB_NAME=ImpAtRestorePoint
TABLES=BAK_EMPLOYEES
LOGFILE=default_log_dest:hrImpAtRestorePoint
Once the import job is finished, a query to the current table shows the data 'as it was',
prior to the update command.
SQL> select sum(salary) from bak_employees;
SUM(SALARY)
-----------
691400
Data Pump export space estimation
Proactively estimating the amount of space required by an export file prevents
physical disk space shortages. Data Pump has two methods to estimate the space
requirements: Estimation by block sampling (
BLOCKS
) or estimation by object
statistics (
STATISTICS
).
ESTIMATE={BLOCKS | STATISTICS}
•
BLOCKS
—The estimate is calculated by multiplying the number of database
blocks used by the target objects times the appropriate block sizes.
•
STATISTICS
—The estimate is calculated using statistics for each table.
For this method to be as accurate as possible, all tables should have been
analyzed recently.
The second method leads to more accurate results and can be performed in a more
efficient way than the
BLOCKS
method; this method requires reliable table statistics.
Search WWH ::
Custom Search