Difference between beginexecutereader and executereader (beginexecutereader Vs executereader)

The BeginExecuteReader(...) and EndExecuteReader...() are for performing the
ExecuteReader(...) method asynchronously. If you use ExecuteReader(...)
your thread is blocked while that method executes.

Using BeginExecuteReader(...) (and the corresponding EndExecuteReader(...))
ExecuteReader(...) will be executed in a seperate thread, allowing for
yours to continue processing. The BeginExecuteReader(...) method will
require a callback method, and in that callback method, you will make a
call to EndExecuteReader(...) to end the asynchronous operation, and
retreive the return value.