A Database Instance is an interface between client applications (users) and therefore the database. An Oracle instance consists of three main parts: System Global Area (SGA), Program Global Area (PGA), and background processes.

The SGA may be a shared memory structure allocated when the instance started up and released when it’s shut down . The SGA may be a group of shared memory structures that contain data and control information for one database instance.

Different from the SGA, which is out there to all or any processes, PGA may be a private memory area allocated to every session when the session started and released when the session ends.

Major Oracle Database’s background processes

The following are the main background processes of an Oracle instance:

PMON is that the process monitor that regulates all other processes. PMON cleans up abnormally connected database connections and automatically registers a database instance with the listener process. PMON may be a process that has got to be alive in an Oracle database.
SMON is that the system monitor process that performs system-level clean-up operation. it’s two primary responsibilities including automatically instance recovery within the event of a failed instance, e.g., power outage and cleaning from temporary files.
DBWn is that the database writer. Oracle performs every operation in memory rather than the disk because processing in memory is quicker and more efficient than on disk. The DBWn process reads data from disk and writes it back to the disk. An Oracle instance has many database writers DBW0, DBW1, DBW2, and so on.
CKPT is that the checkpoint process. In Oracle, data that’s on disk is named block and therefore the data which in memory is named buffer. When a block is written to the buffer and altered , the buffer becomes dirty, and it must be written right down to the disk. The CKPT process updates the control and file headers with checkpoint information and signals writing of dirty buffers to disk. Note that Oracle 12c allows both full and incremental checkpoints.

LGWR is that the log writer process which is that the key to the recoverability architecture. Every change occurs within the database is written bent a file called redo log for recovery purposes. And these changes are written and logged by LGWR process. The LGWR process first writes the changes to memory then disk as redo logs which then are often used for recovery.
ARCn is that the archiver process that copies the content of redo logs to archive redo log files. The archiver process can have multiple processes like ARC0, ARC1, and ARC3, which permit the archiver to write down to varied destinations like D: drive, E drive or other storage.
MMON is that the manageability monitor process that gathers performance metrics.
MMAN is that the memory manager that automatically manages memory in an Oracle database.
LREG is that the listener registration process that registers information on the database instance and dispatcher processes with the Oracle Net Listener.

Now, you ought to have an honest overview of the Oracle Database architecture and its components

Introduction to the Oracle Listener

The listener may be a separate database server process that runs locally on the database server or remotely on the Oracle RAC environment.

This picture shows the Oracle Database architecture and where the listener locates:

When a client request comes, the listener first receives it. then it establishes a connection between the client and therefore the database instance.

Once the client is connected to the database instance successfully, it hands over the client connection to the server process.

If the listener stops running, you can’t hook up with the Oracle Database anymore. However, all the prevailing connections won’t be affected.

Oracle Listener control commands

To launch the listener control, you employ the LSNCTRL command from the instruction on Windows or terminal on Linux:

lsnrctrl

Type the assistance command to ascertain all available options:

LSNRCTL> help

Here is that the output:

The following operations are available

An asterisk (*) denotes a modifier or extended command:

start stop status services

version reload save_config trace

quit exit set* show*

You can use all of those commands to regulate the listener. Let’s use the status command:

LSNRCTL> status

The output shows the status of the listener like alias, version, start date, uptime, trace file, security, listener parameter files listener log files and listening endpoint summary.

Now, issue the stop command:

LSNRCTL> stop

Once the listener stop listening, you can’t hook up with the Oracle Database anymore. Any plan to hook up with the Oracle Database will end in the subsequent error:

ORA-12541: TNS:no listener

Note that each one connections established before the listener stopped are going to be unaffected. Because stopping the listener prevents the incoming connections, it doesn’t disconnect people who are already connected.

Use the beginning command to mention the listener:

LSNRCTL> start

To exit the listener, you employ the exit command:

LSNRCTL> exit

Another way to execute the listener command is thru the instruction without going into the listener control interface. for instance , to look at the status of the listener, you’ll use the subsequent command within the instruction on Windows or Terminal on Linux:

lsnrctl status

On Windows, the Oracle listener features a service running as TNS listener. you’ll also control the status of the listener via this service by stopping and starting it.

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Introduction to Oracle Database

What is the Oracle Database
Pre-requisites for oracle database
Oracle database 12c installation
Multi-tenant architecture

Exploring the Oracle 12c Database Architecture

Explain the Memory Structures
Describe the Process Structures
Overview of Storage Structures

Preparing the Database Environment

Identify the tools for Administering an Oracle Database
Plan an Oracle Database Installation
Install the Oracle Software by using Oracle Universal Installer (OUI)
Create a Database by using the Database Configuration Assistant (DBCA)

Managing the Oracle Instance

Setting database initialization parameters
Describe the stages of database startup and shutdown

Database Storage Structures and Schema Objects

Managing Database Storage Structures
Overview of table space and data files
Overview of Primary Components
Identify the importance of checkpoints, redo log files, and archived log files
Configure ARHIVELOG mode

Database Startup & User Requests and Oracle Network Environment

Describe the stages of database startup and shutdown
Using alert log and trace files
Configure and Manage the Oracle Network
pFile and spFile
Tablespace Management
Storage and Relationship Structure

Oracle Backup & Recovery

Redo log File Management
Performing Database Recovery
Overview of Data Recovery Advisor
Use Data Recovery Advisor to Perform recovery (Control file, Redo log file and Data file)

Deep Dive into Oracle Recovery Manager (RMAN)

Using the RMAN Recovery Catalog
Identify situations that require RMAN recovery catalog
Create and configure a recovery catalog
Synchronize the recovery catalog
Create and Use RMAN stored scripts
Back up the recovery catalog
Create and use a virtual private catalog

Configuring Backup Specifications

Using RMAN to Create Backups
Create image file backups
Create a whole database backup
Enable fast incremental backup
Using RMAN to Perform Recovery
Perform complete recovery from a critical or noncritical data file loss using RMAN
Perform incomplete recovery using RMAN

Data Movement and Oracle Data Pump

Moving Data
Describe and use methods to use move data (Directory objects, SQL* Loader, External tables)
Explain the general architecture of Oracle Data Pump

Data Dictionary & Dynamic Performance Tables

Oracle Data Dictionary contains information related to database privileges
Data dictionary views
Media failure
Flashback CDB

Database Tuning

What is database tuning
How to tune the database
Tuning the data dictionary

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