You can use OpenXml SDK for *.xlsx files. It works very quickly. I made simple C# IDataReader implementation for this sdk. See here. Now you can easy import excel file to sql server database using SqlBulkCopy. It uses small memory because it reads by SAX(Simple API for XML) method (OpenXmlReader)
Example:
private static void DataReaderBulkCopySample()
{
using (var reader = new ExcelDataReader(@"test.xlsx"))
{
var cols = Enumerable.Range(0, reader.FieldCount).Select(i => reader.GetName(i)).ToArray();
DataHelper.CreateTableIfNotExists(ConnectionString, TableName, cols);
using (var bulkCopy = new SqlBulkCopy(ConnectionString))
{
// MSDN: When EnableStreaming is true, SqlBulkCopy reads from an IDataReader object using SequentialAccess,
// optimizing memory usage by using the IDataReader streaming capabilities
bulkCopy.EnableStreaming = true;
bulkCopy.DestinationTableName = TableName;
foreach (var col in cols)
bulkCopy.ColumnMappings.Add(col, col);
bulkCopy.WriteToServer(reader);
}
}
}