performance is slow with hibernate and MS sql server

I'm using hibernate and db is sqlserver. SQL Server differentiates it's data types that support Unicode from the ones that just support ASCII. For example, the character data types that support Unicode are nchar, nvarchar, longnvarchar where as their ASCII counter parts are char, varchar and longvarchar respectively. By default, all Microsoft’s JDBC drivers send the strings in Unicode format to the SQL Server, irrespective of whether the datatype of the corresponding column defined in the SQL Server supports Unicode or not. In the case where the data types of the columns support Unicode, everything is smooth. But, in cases where the data types of the columns do not support Unicode, serious performance issues arise especially during data fetches. SQL Server tries to convert non-unicode datatypes in the table to unicode datatypes before doing the comparison. Moreover, if an index exists on the non-unicode column, it will be ignored. This would ultimately lead to a whole table scan during data fetch, thereby slowing down the search queries drastically.

The solution 开发者_如何学Gowe used is ,we figured that there is a property called sendStringParametersAsUnicode which helps in getting rid of this unicode conversion. This property defaults to ‘true’ which makes the JDBC driver send every string in Unicode format to the database by default. We switched off this property.

My question is now we cannot send data in unicode conversion. in future if db column of varchar is changed to nvarchar (only one column not all varchar columns), now we should sent the string in unicode format.

Please suggest me how to handle the scenario.

Thanks.

You need to specify property: sendStringParametersAsUnicode=false in connection string url.

jdbc:sqlserver://localhost:1433;databaseName=mydb;sendStringParametersAsUnicode=false

Unicode is the native string representation for communication with SQL Server, if you are converting to MBCS (Multibyte character sets), then you are doing 2 converts for every string. I suggest that if you are concerned with performance, use all Unicode instead of all MBCS

ref: http://social.msdn.microsoft.com/Forums/en/sqldataaccess/thread/249c629f-b8f2-4a8a-91e8-aad0d83919ca