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1.
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What is a Database instance? Explain |
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A database instance (Server) is a set of memory
structure and background processes that access a set of
database files.
The process can be shared by all users.
The memory structure that is used to store most queried
data from database. This helps up to improve database
performance by decreasing the amount of I/O performed
against data file.
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2.
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What is Parallel Server? |
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Multiple instances accessing the same database (Only In
Multi-CPU environments)
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3.
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What is a Schema? |
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The set of objects owned by user account is called the
schema.
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4.
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What is an Index? How it is implemented in Oracle
Database? |
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An index is a database structure used by the server to
have direct access of a row in a table.
An index is automatically created when a unique of
primary key constraint clause is specified in create
table comman (Ver 7.0)
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5.
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What is a cluster? |
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Group of tables physically stored together because they
share common columns and are often used together is
called Cluster.
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6.
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What is a cluster Key? |
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The related columns of the tables are called the cluster
key. The cluster key is indexed using a cluster index
and its value is stored only once for multiple tables in
the cluster.
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7.
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What is the basic element of Base configuration of an
oracle Database? |
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It consists of
one or more data files.
one or more control files.
two or more redo log files.
The Database contains
multiple users/schemas
one or more rollback segments
one or more tablespaces
Data dictionary tables
User objects (table,indexes,views etc.,)
The server that access the database consists of
SGA (Database buffer, Dictionary Cache Buffers, Redo log buffers,
Shared SQL pool)
SMON (System MONito)
PMON (Process MONitor)
LGWR (LoG Write)
DBWR (Data Base Write)
ARCH (ARCHiver)
CKPT (Check Point)
RECO
Dispatcher
User Process with associated PGS
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8.
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What is a deadlock? Explain. |
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Two processes waiting to update the rows of a table
which are locked by the other process then deadlock
arises.
In a database environment this will often happen because
of not issuing proper row lock commands. Poor design of
front-end application may cause this situation and the
performance of server will reduce drastically.
These locks will be released automatically when a
commit/rollback operation performed or any one of this
processes being killed externally.
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9.
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What is SGA? How it is different from Ver 6.0 and Ver
7.0? |
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The System Global Area in a Oracle database is the area
in memory to facilitates the transfer of information
between users. It holds the most recently requested
structural information between users. It holds the most
recently requested structural information about the
databse.
The structure is Database buffers, Dictionary cache,
Redo Log Buffer and Shared SQL pool (ver 7.0 only) area.
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10.
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What is a Shared SQL pool? |
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The data dictionary cache is stored in an area in SGA
called the Shared SQL Pool. This will allow sharing of
parsed SQL statements among concurrent users.
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11.
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What is mean by Program Global Area (PGA)? |
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It is area in memory that is used by a Single Oracle
User Process.
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12. |
What is a data segment? |
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Data segment are the physical areas within a database
block in which the data associated with tables and
clusters are stored.
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13.
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What are the factors causing the reparsing of SQL
statements in SGA? |
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Due to insufficient Shared SQL pool size.
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14.
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What is Distributed database? |
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A distributed database is a network of databases managed
by multiple database servers that appears to a user as
single logical database. The data of all databases in
the distributed database can be simultaneously accessed
and modified.
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15.
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What is Two-Phase Commit? |
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Two-phase commit is mechanism that guarantees a
distributed transaction either commits on all involved
nodes or rolls back on all involved nodes to maintain
data consistency across the global distributed database.
It has two phase, a Prepare Phase and a Commit Phase.
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16.
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Describe two phases of Two-phase commit? |
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Prepare phase - The global coordinator (initiating node)
ask a participants to prepare (to promise to commit or
rollback the transaction, even if there is a failure)
Commit - Phase - If all participants respond to the
coordinator that they are prepared, the coordinator asks
all nodes to commit the transaction, if all participants
cannot prepare, and the coordinator asks all nodes to
roll back the transaction.
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17.
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What is the mechanism provided by ORACLE for table
replication? |
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Snapshots and SNAPSHOT LOGs
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18.
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What is a SNAPSHOT? |
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Snapshots are read-only copies of a master table located
on a remote node which is periodically refreshed to
reflect changes made to the master table.
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19.
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What is a SNAPSHOT LOG? |
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A snapshot log is a table in the master database that is
associated with the master table. ORACLE uses a snapshot
log to track the rows that have been updated in the
master table. Snapshot logs are used in updating the
snapshots based on the master table.
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20.
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What is a SQL * NET? |
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SQL *NET is ORACLE's mechanism for interfacing with the
communication protocols used by the networks that
facilitate distributed processing and distributed
databases. It is used in Clint-Server and Server-Server
communications.
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