In SAS 8 and earlier,
SAS opened a single connection to the DBMS to read a table. SAS statements
requesting data were converted to an SQL statement and passed to the
DBMS. The DBMS processed the SQL statement, produced a result set
consisting of table rows and columns, and transferred the result set
back to SAS on the single connection.
With a threaded Read,
you can reduce the table read time by retrieving the result set on
multiple connections between SAS and the DBMS. SAS can create multiple
threads, and a read connection is established between the DBMS and
each SAS thread. The result set is partitioned across the connections,
and rows are passed to SAS simultaneously (in parallel) across the
connections, which improves performance.