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82 Oracle Architecture and Concepts Questions and Answers:
A database link is a pointer that defines a one-way communication path from an Oracle Database server to another database server. The link pointer is actually defined as an entry in a data dictionary table. To access the link, you must be connected to the local database that contains the data dictionary entry.
A materialized view is a replica of a target master from a singlepoint in time. The concept was first introduced with Oracle7 termed asSNAPSHOT. In Oracle release 7.1.6 snapshots were enhanced to enableDMLs along with a new terminology, updatable snapshots. With Oracle8.1.6 snapshots started to be used in data warehouse environments so anew terminology materialized view was introduced to address bothdistributed and data warehouse materialized views.
It's an oracle object as other object like table. It stores index key + rowid for that key. So when you scan index it finds respective rowid and fetch data from that rowid. and it's faster
Rollback Segment and
Rollback Segment and
A rule defined on a column (or set of columns) in one table that allows the insert or update of a row only if the value for the column or set of columns (the dependent value) matches a value in a column of a related table (the referenced value). It also specifies the type of data manipulation allowed on referenced data and the action to be performed on dependent data as a result of any action on referenced data.
It stores your uncommited temporart data. ex. If you do any insert/update/delete and you won't commit it is written in rollback segment.
Index is a Database object . It can be accessed rows physical fast. when you move the table from different table spaces or same table spaces indexes will unusually status. So You compulsory rebuild the index. Rebuilding the index is very fast than drop and create the new indexes.
8 :: Explain can an Integrity Constraint be enforced on a table if some existing table data does not satisfy the constraint?
Yes.Use Enable Novalidate to enforce the constraints. Existing data will not be checked, only new/update will be validated.
Yes as U said,If on one side a query is executed and simultaneously a DML is happening at the same time. THEN the user doing the DML action gives a commit in between while the query is still executing on the other side then, on the query side U get this message "SNAPSHOT TOO OLD"Suggestion :Alter system set UNDO_retention = 900 ;or give a large value for undo retention, ie., the undo block will be kept in the memory until 900 microseconds even after the commit transaction on the same table, so that the query ends within that.
Controlfile contains the information about the database like names and locations of datafiles, name of the database, database creation timestamp and apart from this the SCN are also reported into control during the database operation. Especially during the database startup the controlfile is used to gather the information about the database and while opening the database the information in the controlfile is validated to check for the consistency of the database.