THAN MYSQL 5.1".

MySQL 5.6 has shown somewhat worse performance than MySQL 5.1
for SysBench read-only/InnoDB workload against several tables
for low number of connections.

This issue was caused by the contention in MDL subsystem
introduced in 5.5. The particular source of contention was
MDL_map::m_mutex which protects hash containing all MDL_lock
objects in the system.

This patch addresses the problem by partitioning this hash
and corresponding mutex by key for MDL_lock objects, thus
allowing connections accessing different tables/objects to
work with different partitions and therefore avoid contention.

New start-up parameter --metadata-locks-hash-instances is
introduced which allows to specify number of such partitions
(with 8 partitions as default value).