Removing Non-Essential Indexes and Constraints during a Load


You want to improve the performance of a job that includes a table that contains one or more non-essential indexes.


You can remove non-essential indexes before a load and recreate those indexes after the load. In some situations, this procedure improves performance. As a general rule, consider removing and recreating indexes if more than 10 percent of the data in the table requires reloading.
You might also want to temporarily remove key constraints in order to improve performance. If you remove constraints from the target before the load, then you remove the overhead of maintaining those constraints. If you are loading a significant number of transactions with data that conforms to the constraints, then removing the constraints should improve your performance.
To control the timing of index and constraint removal, use the options that are available on the Load Technique tab of the Table Loader transformation. The following settings are provided to enable you to specify the desired conditions for the constraints and indexes before and after the load:
  • the Before Load field in the Constraint Condition group box
  • the After Load field in the Constraint Condition group box
  • the Before Load field in the Index Condition group box
  • the After Load field in the Index Condition group box
The options that are available depend on the load technique that you choose. The choices translate to four different tasks: put on, take off, leave as is, or recreate as is. When you select Off for the Before Load options, the generated code checks for and removes any indexes (or constraints) that are found. Then, it loads the table. If an index is required for an update, that index is added or not removed as needed. Select On for the After Load options to have indexes added after the load.
In some situations, you might select Leave Off in the After Load field to leave the indexes off during and after the table loading for performance reasons. One scenario is when the table is updated multiple times in a series of load steps. Indexes are defined on the table only to improve performance of a query and reporting application that runs after the nightly load. None of the load steps need the indexes, and leaving the indexes on impedes the performance of the load. In this scenario, the indexes can be taken off before the first update and left off until after the final update.