It produces a series of unique numbers in a multi-user environment without
the overhead of disk locking or any special I/O calls, other than what is involved in loading the
sequence into the shared pool.
Sequences can generate numbers up to 38 digits in length; the series of numbers can be
ascending or descending, the interval can be any user-specified value, and Oracle can cache
blocks of numbers from a sequence in memory for even faster performance.
The numbers from sequences are guaranteed to be unique, but not necessarily sequential.
If a block of numbers is cached, and the instance is restarted, or a transaction that uses a number
from a sequence is rolled back, the next call to retrieve a number from the sequence will not
return the number that was not used in the original reference to the sequence.
Synonyms
An Oracle synonym is simply an alias to a database object, to simplify references to database
objects and to hide the details of the source of the database objects. Synonyms can be assigned
to tables, views, materialized views, sequences, procedures, functions, and packages. Like views,
a synonym allocates no space in the database, other than its definition in the data dictionary.
Synonyms can be either public or private. A private synonym is defined in the schema of
a user and is available only to the user. A public synonym is usually created by a DBA and is
automatically available for use by any database user.
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