Практика Shadowing: Oracle database architecture explanation in details - Изучайте разговорный английский с YouTube

Hi friends, today in this video I am going to talk about Oracle Database.

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Hi friends, today in this video I am going to talk about Oracle Database.

Oracle Database is basically one of the most demanding database which has started by Oracle Corporation in 1971.

So even when you are starting your career as Oracle Database,

in most of the interview you will get so many questions from Oracle Database Architect.

So in that perspective also and even for learning Oracle Database,

this is one of the most demanding topic that you have to must learn with deep understanding.

So I am going to explain with my personal experience on Oracle Database because I am a database administrator.

So with my personal understanding,

with my personal experience, I am going to explain the whole architecture.

so yeah first of all whenever any end user wants to connect

or a database so it connects through use any client machine

or through any application end user application

or even through sql developer there are multiple platform from there you people connects to the database

so you know client machine it will create a user user process

and between user process

and server process there will be a listener listener will have information about the host

and port of an database with on the

with that it will decide which database it has to connect so it will it will generate a one dispatch

dispatcher request when that dispatcher will send that request to the server process

and server process are when

when you create a database by default it creates a dedicated server process

and server process basically sits on uh servers oracle server side

so when we create a database it will get created by default it will be a dedicated server process

and for dedicated server process it will create a PGA

that is called program global area but

if you are choosing a shared global area for that it will create UGA that is user global area.

So server process is basically responsible for making that connection to the database

because it's interact to the database so it will send

that request to the database like if we are firing any uh selected statement

or any sql on a database so from server process it will go to a

sga sga is a shared global area basically is the is it's the largest part of the database instance

and the database is basically combination of instance background process

and the physical files so physical files are basically data file redlock file

and control file so these are the physical files and yes SGA is also the combination of different sub components

so in that whenever

that request will come from server process it will it will go to share pool first of all

and in share pool there are two sub components

that one is library cache and another is dictionary cache library cache is basically information of most recently executed SQLs

so most recently executed SQLs are basically when

that request goes from server process to SGA it will do the syntax check like

if that query is selected star from employee

so syntax it will validate from there like

if you execute select from employee it will not execute because the syntax is missed here like star is missed.

So it will not it will throw the error.

So that part is happening from library cache because it will do the syntax check,

cement text check and privilege checks are happening on share pool itself.

So, when the syntax check will happen after that it will validate

if it will find

that yes this SQL is present on the buffer cache then it will fetch

that particular query output

and it will return to the server process it will return to the client machine

and that that's the same process is getting followed for in case

if that particular SQL is not present in library case then it will create a execution plan for that and also like

yes data dictionary case is a metadata of a database like

it will have a object information like table views are stored into this

so it will it will do the validation from data dictionary case as well as

when library case will will not find that particular SQL it will

generate a new execution plan that is basically goes for hard parishing and there is two words

that we use in a database when any SQL get executed on a database side,

it will go to soft parishing either it will go to hard parishing.

So, soft parishing is the first case where it will find the SQL from the library cache itself

and then it will fetch the data from memory buffer cache memory and it will return to the client.

But in hard parishing case,

will create a new execution plan and it will go for optim or through a optimization in that it will

it will it will check from the buffer case if

that not there then after creating execution plan it will then the background process will come into the picture

and db writer will fetch that

DB writer will fetch

that particular data as per the query request it will fetch the data from the data file

and it will return to the library cache and library cache will

buffer cache sorry buffer cache and then DB buffer cache will return that

to server process and server process will return to the client so that's how

it works

so the next is as we know buffer cache is doing

all the things whatever the queries are coming it is getting executed in buffer cache itself

and it stores the in case

if you are executing any like a database change statement queries like insert or create or something like any DML.

So in those situation it will do the changes on the data

and in that situation read log and online read log and buffer

read log buffer will come into the picture so there first of all buffer case will change that

after doing the modification on the query it will get converted into a dirty buffer

and that dirty buffer will get written to the online reader log it might be uncommitted transaction

or it may it may be a committed transaction

so both can be possible

and from a read a log buffer it will get written

to the read a log file through log writer log writer

is responsible it's also a background process these are basically a

mandatory background process background processes are basically two type back mandatory background process and optional background process so

library cache is a mandatory background process

which is responsible for copying online redlock buffers to the online redlock files

so here redlock files are basically two online redlocks we can create like as per need we create

that redlock files so first it will start writing to read log one after

that once it will get filled up it will done the online read log switch will happen

and then it will start writing to second online read log so that's how whatever the change

transaction change modified data will come from online read log buffer to the

read log it will get written to log 1 and log 2

and similarly till the time after

that it will get written to through archiver process there is a optional optional background process

that is called archiver with with the help of

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that it will get written to the archive read log

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that we'll use for our backup

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and recovery of our database in case i am our database fails

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or it get crashed for any reason so that will be used for recovery so yeah so the next is

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assist if we focus of our mandatory background process

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so as one is system monitors as money is basically used for instance recovery

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and yeah even for temporary table space management also it

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will be responsible PMON is responsible for our transaction transition rollback

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and for PMON is process monitor which is responsible for user session recovery

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and doing the cleanup or even rollback statements this is responsible for making those cleanups on database

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and yeah check pointer is a background process which is updating the scn number to data file and on

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control control control file control file is a brain of a database

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which will which will have information about the database creation and all the data file information and detail about the database.

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So, this control file will be considered as a brain of a database.

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So, SCN number whenever SCN number is getting generated very frequently through whenever the check pointer occurs,

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the time SCN number is getting generated and

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that is getting updated to the header of a data file

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and control red log control file so yes there are some condition

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when the log writer writes log writer writes whenever the online red log is more than 1 GB

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or its one third full

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or even every 3 second log writer writes the data on the buffer read log buffers to the online read log files.

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So similarly there are few condition on

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that basis DB writer writes those online read logs to the

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online buffer cases changes to the data file like whenever the buffer case dirty buffer is filled up

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or even its its there is no space left in the buffer cache

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or even whenever any trunk truncate or any drop statement table space drop

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or truncate statements are getting executed or even for every commit basically the DB writer writes and log writer

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before the DB writer so that is also one condition

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when log writer writes so these are the condition

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when the log writer writes so apart from there is a parameter file

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and password file parameter file is basically a file

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which will it's a file which stores the information of every component which is

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showing on the figure as a shared pool sga sga max sga target

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and buffer cache a red log java pool large pool this

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uh parameters uh this this components are uh declared into a

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parameter file with how much size we we need it so those things are declared all the instance related come

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parameters are declared into parameter file

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so parameter files is two type like one is P file

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and the another is SP file P file we we called it any dot aura file

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and the this file is basically a static file

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and SP file is a dynamic file so

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if we are doing any change in p file for

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that we have to restart our database

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and basically for for starting our instance p file is responsible to to allocate the sga

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so p file is equally important without p file we our database cannot run

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and the next is password file it is used for user authentication

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so this is the whole thing about the database in

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that data file is actual physical file

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and read lock files are all the change transactions are getting stored into

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that and control file already I explained it

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so this is the whole thing about the database

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and this all components are like very much important yeah Java

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pool basically this Java pool are getting used at the time

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when you execute a statement with jvm or java related uh statements for

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that case java pool is getting used

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and large pool is getting used at the time

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when uh we are performing any uh arman backup with i um higher higher io

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and for our recovery um yeah for database recovery

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in those conditions large pool is getting utilized

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so this is the whole database instance that i have explained

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if you any doubt please comment below thanks for watching till here

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