Optimize Oracle import (imp) performance Don Burleson

Note:  This is a quick overview of improving data pump import performance for beginners.  For expert-only tips on improving SQL*Loader speed, see here.  Also see my notes on tuning and improving Oracle export (expdp) performance speed.

Regardless of which options were used when the data was exported, it has 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, since it is a plain export file, be it 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 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. 

Hidden parameters - You can also use the hidden parameter _disable_logging = true to reduce redo, but beware that the resulting import will be unrecoverable.

Import Speed Benchmarks:

Monitoring import performance

Monitoring Oracle Data Pump import performance is simple

select
   substr(sql_text,instr(sql_text,'into "'),30) table_name,
   rows_processed, round((sysdate-to_date(first_load_time,'yyyy-mm-dd hh24:mi:ss'))*24*60,1) minutes,
   trunc(rows_processed/((sysdate-to_date(first_load_time,'yyyy-mm-dd hh24:mi:ss'))*24*60)) rows_per_minute
from  
   sys.v_$sqlarea
where 
   sql_text like 'insert %into "%' and command_type = 2 and open_versions > 0;

Also see: