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     Oracle Utilities Tips

Maximizing Import Performance

The options used when the data is exported have no influence on how the data is imported. For example, it is irrelevant to the import process whether it was a direct path export or not. The result is a plain export file whether is was generated from direct or conventional means.  

Unfortunately, there is no direct option available for imports (only for export and SQL*loader).  The import process has more tuning limitations than other utilities.  The Remote DBA should consider the following when trying to optimize import performance:

·     Set commit=n – For tables that can afford not to commit until the end of the load, this option provides a significant performance increase.  Larger tables may not be suitable for this option due to the required rollback/undo space.

·     Set indexes=n – Index creation can be postponed until after import completes, by specifying indexes=n.  If indexes for the target table already exist at the time of execution, import performs index maintenance when data is inserted into the table.  Setting indexes=n eliminates this maintenance overhead.

·     Use the buffer parameter – By using a larger buffer setting, import can do more work before disk access is performed. 

When tuning import, emphasize reducing the amount of work that import needs to do.  This can be accomplished by committing less frequently, not importing indexes, not generating statistics, or by using the buffer parameter to reduce disk access. 

For the table with one million rows, the following benchmark tests were performed using the different import options.  The table was truncated after each import. 


Import Option

Elapsed Time (Seconds)

Time Reduction 













buffer = 64000



Table 4.2 - Shows that increasing the size of the buffer has a positive performance impact. 

The table above shows that increasing the size of the buffer has a positive performance impact.  However, the most dramatic increase in performance was obtained when setting commit=n.   The increase in the size of the buffer resulted in a marginal improvement when commit=n.  

Before devising a strategy for using export / import to copy data from one database to another, the SQL*Plus copy command should be considered.

Import Speed Benchmarks:

 Oracle guru Steve Callan notes that he has run parallel Data Pump import jobs to load 1.8 terabytes (1,800 gigabytes) in less than a day, an import load rate of over 75 gigabytes per hour.

“The target box was an AIX 5L using LPARS, pretty sure it was 32 CPU and 64GB RAM. There were several distinct schemas, so the data pump export/import was a matter of divide and conquer (i.e., stream several jobs/sessions). I think the largest chunk was around 900GB.

Statistics gathering took a while, but that time was separate from the actual import, and some indexes were skipped/re-built later.  

An old import version of this lasted right around three days, and the data pump version was about a third of that time.”  

As we see, the import speed is far greater using the newer Data Pump import utility (impdp) and imports run faster of faster servers.

For professionals only:  This is a expert-only overview of improving data pump import performance. 

For beginners: see here.

To learn more about these techniques, see the book "Advanced Oracle Utilities: The Definitive Reference". 

You can buy it directly from the publisher and get instant access to the code depot of utilities scripts.




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