[From Builder AU]
STS is a part of Oracle 10g’s SQL Tuning Advisor feature. Each tuning set contains one or more SQL statements, plus the context information needed to interpret them correctly. A tuning set is used as input to the SQL Tuning Advisor, which examines the statements and makes recommendations for improving them.
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http://www.builderau.com.au/program/oracle/soa/Move-SQL-Tuning-Sets-between-Oracle-instances/0,339028441,339292232,00.htm