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Teach yourself Oracle8 in 21 day

it requests information from the database. Any read-only SQL statement can be thought
of as a query.
<H2><FONT COLOR="#000077">R</FONT></H2>
<P><B>random I/O</B>--Occurs when data is accessed on a disk drive in no specific
order. Random I/O typically creates significant disk-head movement.</P>
<P><B>read consistency</B>--An attribute used to ensure that, during a SQL statement,
data returned from Oracle is consistent. Oracle uses the rollback segments to ensure
read consistency.</P>
<P><B>recursive call</B>--A set of SQL statements generated by Oracle in response
to some action or event.</P>
<P><B>redo log file</B>--The file that contains a copy of all data blocks that have
been modified as the result of a database transaction. In the event of a system failure,
any transaction can be recovered with these redo blocks. Oracle requires at least
two redo log files that are written to in a round-robin fashion.</P>
<P><B>referential integrity</B>--A constraint on a column in a table that references
another column. The constraint can be used to guarantee that the referenced value
exists.</P>
<P><B>replication</B>--The creation of an image of a database or table on another
computer system. A <B>replicated database</B> is a copy of another database.</P>
<P><B>rollback</B>--The act of undoing changes that have been made by a transaction.</P>
<P><B>rollback segment</B>--The place in the database where undo information is kept
and can be obtained if a rollback is needed.</P>
<P><B>rules-based optimizer</B>--The Oracle optimizer that chooses an execution plan
based on a table of costs associated with various operations.
<H2><FONT COLOR="#000077">S</FONT></H2>
<P><B>scalability</B>--Typically used in association with multiprocessor or cluster
configurations. The scalability of the additional component refers to the performance
gain obtained by adding that component. A perfectly scalable solution gives double
the performance when you add a second component.</P>
<P>For example, if you have an SMP machine with a measured performance of 1.0 (normalized),
add a second CPU, and get a performance of 1.9, the scalability of adding the second
CPU is 1.9, or 90%. This term is used quite frequently in hardware and software manufacturers'
literature when marketing multiprocessor or clustered solutions.</P>
<P><B>schema</B>--A collection of objects associated with the database.</P>
<P><B>schema objects</B>--Abstractions or logical structures that refer to database
objects or structures. Schema objects consist of such things as clusters, indexes,
packages, sequences, stored procedures, synonyms, tables, views, and so on.</P>
<P><B>SCN</B>--System Change Number. The SCN is a number that identifies each change
to the database. The SCNs are used during the checkpoint process, recovery process,
and during point-in-time recovery.</P>
<P><B>segment</B>--The set of extents that have been allocated to a specific object.
Segment types consist of data, index, cluster, hash, and rollback.</P>
<P><B>self join</B>--A join in which a table is joined with itself.</P>
<P><B>sequences</B>--A convenience feature of Oracle that allows unique sequential
numbers to be automatically generated for you.</P>
<P><B>sequential I/O</B>--Occurs when data is accessed on a disk drive in order.
Sequential I/O typically causes very little disk-head movement.</P>
<P><B>Server Manager</B>--Oracle's GUI database administration tool. Server Manager
is used to replace SQL*DBA.</P>
<P><B>session</B>--The set of events that occurs from when a user connects to the
Oracle RDBMS to when that user disconnects.</P>
<P><B>SGA</B>--System Global Area. The SGA is a shared memory region Oracle uses
to store data and control information for one Oracle instance. The SGA is allocated
when the Oracle instance starts; it is deallocated when the Oracle instance shuts
down. Each Oracle instance that starts has its own SGA. The information in the SGA
is made up of the database buffers, the redo log buffer, and the shared pool; each
has a fixed size and is created at instance startup.</P>
<P><B>shared pool</B>--The area in the SGA that contains the data dictionary cache
and shared parsed SQL statements.</P>
<P><B>simple statement</B>--A SQL statement that involves only one <TT>INSERT</TT>,
<TT>UPDATE</TT>, or <TT>DELETE </TT>statement.</P>
<P><B>SMP</B>--Symmetric Multiprocessor. An SMP system is a multiprocessor computer
that uses a shared-memory architecture. SMP systems are usually either a tightly
coupled or a loosely coupled architecture.</P>
<P><B>snapshot</B>--A copy of a database or table. This term is used in relation
to database replication.</P>
<P><B>SPX/IPX</B>--A network protocol developed for the NetWare operating system.
Today, SPX/IPX runs on many operating systems.</P>
<P><B>SQL*DBA</B>--The Oracle database administration tool. SQL*DBA is being made
obsolete by Server Manager.</P>
<P><B>SQL*Loader</B>--The Oracle database loading tool.</P>
<P><B>SQL*Net</B>--The Oracle component that allows connections from a network into
the Oracle RDBMS. SQL*Net supports many protocols; SQL*Net on any architecture can
talk to SQL*Net on any other supported architecture.</P>
<P><B>SQL*Plus</B>--An Oracle-supplied tool that allows users to run SQL statements
directly.</P>
<P><B>streaming</B>--Usually associated with a tape device. Tapes perform best when
the tape is continually in motion, or streaming. If the data is not fed to the tape
quickly enough, the tape drive must reposition the tape to wherever it last stopped
recording data (to reposition the tape, the drive must stop the tape and rewind it).
This action severely degrades performance.</P>
<P><B>stored function</B>--<I>See</I> <B>function</B>.</P>
<P><B>stored procedure</B>--<I>See</I> <B>procedure</B>.</P>
<P><B>subquery</B>--A <TT>SELECT</TT> statement referenced in an <TT>UPDATE</TT>,
<TT>INSERT</TT>, or <TT>DELETE</TT> statement.</P>
<P><B>swapping</B>--An operating system function similar to paging; used to copy
virtual memory between physical memory and the paging file (<I>see</I> <B>virtual
memory</B>). Swapping is almost identical to paging except that swapping is done
on a process basis and paging is done on a memory-page basis. Swapping is used when
the amount of virtual memory in use has exceeded the amount of physical memory available.
Swapping is quite expensive in terms of performance and should be avoided if possible.</P>
<P><B>Symmetric Multiprocessor</B>--<I>See</I> <B>SMP</B>.</P>
<P><B>synonym</B>--An alias for a table, view, sequence, or program unit.</P>
<P><B>System Change Number</B>--<I>See</I> <B>SCN</B>.</P>
<P><B>System Global Area</B>--<I>See</I> <B>SGA</B>.
<H2><FONT COLOR="#000077">T</FONT></H2>
<P><B>table</B>--The basic unit of storage in the Oracle database. Users store their
data in tables.</P>
<P><B>tablespace</B>--A logical structure that consists of one or more datafiles.
A tablespace is used to logically contain tables, clusters, and indexes.</P>
<P><B>TCP/IP</B> (<B>Transmission Control Protocol/Internet Protocol)</B>--A network
protocol. TCP/IP is probably the most used network protocol in the world.</P>
<P><B>thread</B>--Sometimes know as a <B>lightweight process</B>. Similar to a process
but shares the process context with other threads. A thread has much less overhead
associated with it than does a normal process. A <B>thread switch </B>(change between
threads) has much less overhead than a process switch.</P>
<P><B>Token Ring</B>--A hardware network standard. Token Ring networks use a token-passing
mechanism for arbitration. Only the NIC with the token can use the network.</P>
<P><B>transaction</B>--A set of database statements that represents a logical unit
of work or function. A database transaction starts when the first SQL statement is
submitted and ends when the <TT>COMMIT</TT> or <TT>ROLLBACK</TT> has occurred. Performance
measurements often use the number of transactions per second as the performance metric.</P>
<P><B>trigger</B>--A mechanism that allows you to write procedures that are automatically
executed whenever an <TT>INSERT</TT>, <TT>UPDATE</TT>, or <TT>DELETE</TT> statement
is executed on a table or view. Triggers can be used to enforce integrity constraints
or automate some other custom function.</P>
<P><B>two-phase commit</B>--The process by which distributed transactions occur.
In a two-phase commit, each node commits its changes and signals that it has completed.
When all nodes have successfully committed, the distributed transaction has committed.
<H2><FONT COLOR="#000077">U</FONT></H2>
<P>UPDATE--The SQL statement used to change rows in a table.
<H2><FONT COLOR="#000077">V</FONT></H2>
<P><B>view</B>--A window into a table or set of tables. A view is a way for a table
or set of tables to be seen. A view, like a table, can be queried, updated, inserted
into, and deleted from. The data, however, is actually stored in the tables to which
the view refers.</P>

<P><B>virtual memory</B>--The memory that can be used for programs in the operating
system. To overcome the limitations associated with insufficient physical memory,
virtual memory allows programs to run that are larger than the amount of physical
memory in the system. When there is not enough physical memory in the system, these
programs are copied from RAM to a disk file called a <B>paging file</B> or <B>swap
file</B>. This arrangement allows small systems to run many programs. You pay a performance
penalty when the computer pages or swaps.<FONT COLOR="#000077"></FONT></P>
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