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Why DataSet.Load and DataTable.Load - very slow ?

The DbDataReader object just reads data from database objects. 

The DbDataAdapter.Fill method reads data and caches them in the DataSet object. 

The DataTable.Load method fills a DataTable with values from a data source using the supplied IDataReader and creates constraints. 

The DataSet.Load method fills a DataSet with values from a data source using the supplied IDataReader, using an array of DataTable instances to supply the schema and namespace information. It creates constraints and tables for represeting data. 

In other words, the Load methods require more time, because they make more operations with data.


  1. Testing Data : during tests of SELECT command that DataSet.Load and DataTable.Load methods are much slower compared to other methods of reading data (using DbDataReader or with DbDataAdapter.Fill method). I've got following times:

    Data read with DbDataReader object:
    - Time: 2671.875ms
    Data read with DataSet.Load method:
    - Time: 11546.875ms
    Data read with DataTable.Load method:
    - Time: 11437.5ms
    Data read using DbDataAdapter.Fill method:
    - Time: 3125ms

    In each test 90564 rows were read from database (from two tables) and stored into data set (into two data tables). In DbDataReader's test, data tables were created and filled row-by-row with DataTable.LoadDataRow method.

    Clearly Load methods are almost 5 times slower. Is there any explanation for this. At the beginning I thought that this slow down is caused by constraints checking but disabling it (setting EnforceConstraints property of DataSet object to false) didn't change anything.


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