Scenario : I have the choice of manipulating database data using a String or a java.sql.Clob. Which has best performance ?

java.sql.Clob

Since, it does not extract any data from the database until you explicitly ask it to.

The Java platform 2 type Clob wraps a database locator (which is essentially a pointer to char). That pointer is a rather large number (between 32 and 256 bits in size) - but the effort to extract it from the database is insignificant next to extracting the full Clob content.

For insertion into the database, you should use a String since data need not been downloaded from the database.

Thus, use the Clob class only for extraction.

Conclusion

Unless you always intend to extract the full textual data stored in the particular table cell, use the java.sql.Clob class for extraction whenever you can.