Support for data retrieval, manipulation, and return
This topic affects the design of am_getnext, am_insert, am_delete,
and am_update.
Enforcing unique-index constraints
The UNIQUE or DISTINCT keyword in a CREATE INDEX or insert
statement specifies that a secondary access method cannot insert multiple
occurrences of a key value. The UNIQUE or DISTINCT keyword in a SELECT
statement specifies that the access method must return only one occurrence
of a key value.
Check isolation levels
The isolation level affects the concurrency between sessions
that access the same set of data.