physical structure:
one or more data files, Two of more log files, One control file.
Logical structure:
Table spaces,
Segments, Extents, Data blocks.
The data files contain all user data in terms of tables, index, and views. The log files
contain the information to open and be recovered, of Undone after a transaction(Rollback).
The control file physical data, media information to open and manage data files .If the
control file is damaged the server will not be able to open are use the database even if the
database is undamaged.
What are the Back ground processes in Oracle and what are they. ?
There are basically 9 Processes but in a general system we need to mention the first five
background processes. They do the house keeping activities for the Oracle and are common in
any system.
a) Data Base Writer(DBWR) ::
Data Base Writer Writes Modified blocks from Database buffer cache to Data Files.This is
required since the data is not written whenever a transaction is commited.
b)LogWriter(LGWR) ::
LogWriter writes the redo log entries to disk. Redo Log data is generated in redo log buffer
of SGA. As transaction commits and log buffer fills, LGWR writes log entries into a online redo
log file.
c) System Monitor(SMON) ::
The System Monitor performs instance recovery at instance startup. This is useful for
recovery from system failure.
d)Process Monitor(PMON) ::
The Process Monitor peforms process recovery when user Process fails. Pmon Clears and
Frees resources that process was using.
e) CheckPoint(CKPT) ::
At Specified times, all modified database buffers in SGA are written to data files by
DBWR at Checkpoints and Updating all data files and control files of database to indicate the
most recent checkpoint.
f)Archieves(ARCH) ::
The Archiver copies online redo log files to archival storal when they are busy.
g) Recoveror(RECO) ::
The Recoveror is used to resolve the distributed transaction in network
h) Dispatcher (Dnnn) ::
The Dispatcher is useful in Multi Threaded Architecture
i) Lckn ::
We can have upto 10 lock processes for inter instance locking in parallel sql.
NORMALIZATION
Normalization is a process of simplifying the relationship between data elements in a
record. Through Normalization a collection of data in a record structure is replaced by successive
record structures that are simpler and more predictable and therefore more manageable. It is
process of reducing redundancy and eliminating the anomalies. (anamali means inconsistent state.)
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