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quick guide to Oracle backup and recovery
using explain plan
primary keys versus unique indexes in Oracle
From: Hatem AHRIZ - Is the EXPLAIN PLAN command only available to DBAs?
PS. The utlxplan.sql script is only available on the
Explain plan is available to all users of teh Oracle
database as long as the DBA has created and granted
access to the plan table (and created a public synonym for
it). Type "Desc plan_table" in sql*plus. If it doesn't
exist ask the DBA to create it and/or grant access to it
and/or create a synonym for it. The utlxplan.sql script is
used to create the plan table in the user's schema.
From: RvNair Hello, i know that primary key means
not null & unique key means i can store null
value,but then why is primary key considered better
than unique key?plz help me thanx in advance,
The other major difference between primary keys and unique keys in Oracle is that a table can have only 1
primary key, although this may be a composite key (composed of more than one column), but can have any
number of unique keys. The primary key constraint is supported automatically by a unique index and
represents the primary access route for the table, secondary indexes can be unique or non-unique. For
example the table "department" might have a primary key of "id" and might have a secondary unique index
on "name". These indexes would ensure that the department id is unique and not null and that the
department name is unique.
From: Narayan - please help me with backup & recovery in oracle9i
The easiest way to take a backup of an Oracle database irrespective of which version you're using is to do a
full cold backup, also known as an offline backup. This involves shutting down the database cleanly - by
entering one of the commands shutdown normal, shutdown immediate or shutdown
transanctional, or using Oracle Enterprise Manager - and then using
operating system commands to copy the data files, control files, redo log files and the parameter file to
another disk or to tape. In the event of an incident requiring recovery of the database, you will be able to
restore it to the point at which the last backup was taken by copying the files back to their original location.
Other backup methods include on-line backups, made whilst the database is still open, by puting a
tablepsace into backup mode temporarily (to suspend writes to objects in that tablespace) so that the files
belonging to the tablespace can be copied. This also requires the database to be running in archivelog
mode, so that the redo logs are archived as they are filled before they are overwritten. Recovery in this
case, involves restoring the lost/corrupted data files and then recovering the database using the archived log
files. The Recovery Manager utility (RMAN) can be used to make database backup (and recovery) easier.
Both of these methods are physical backups. Logical backups can be made using the export utility (or
DataPump utility available in Oracle 10g and above) and database objects (tables,indexes,constraints etc)
recovered using import. The export utility can be used to backup the whole database, the objects belonging
to one or more specified users, or a specified set of tables (and associated indexes). In Oracle 9i and above,
export can be used to backup all the objects in a specified tablespace.
For recommendations on books explaining backup and recovery and other subjects, see our Oracle
resources page. For training in backup and recovery see our scheduled Oracle training courses.
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