SELECT FOR UPDATE SKIP LOCKED is undocumented in Oracle9i and Oracle10g. It is used behind the scenes by Advanced Queuing, a reliable messaging service built into the ORACLE DBMS. Oracle11g Release 1 is the first DBMS release that includes documentation on SELECT FOR UPDATE SKIP LOCKED. The SKIP LOCKED clause improves the scalability of applications that attempt to concurrently update the same set of rows in a table. It eliminates wait time for TX locks. Consistency and isolation are preserved. The DBMS server assigns a fair share of the rows to each database client that is interested in an overlapping result set.
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