Oracle RAC DBA Training :DBA Technologies

7/22/2019 Oracle RAC DBA Training :DBA Technologies

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WELCOME TO DBA TECHNOLOGIES

ORACLE DATABASE ARCHITECTURE-2

By

Mr. PRASAD MYNUMPATI18Years Real Time in INDIA-USA

www.dbatechnologies.net

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database Architecture USER TSUSER tablespace is to store datapermanently

Entire Application data storage and retrievalfrom USER tablespaces

For load balancing purpose we use different

tablespaces on different disks for INDEX andDATA

How many tablespaces for a database?depends on design of the application and

number of applications


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ORACLE & OS comparisonFILE SYSTEM TABLESPACE

File system Partitions (ext3) Tablespaces (Undo, Temp and Permanent)

Mount file system (To read and write) By default TS is mounted

Files & Directories Tables , Indexes (objects)

OS Block size TS Block size (Default 8K)

Multi user access based on privileges Multi users access by assigned quota

Backup FS Backup tablespace

FS consistency (fsck) Database level consistency (RMAN)


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Server & Storage configuration

OS and ORACLE SW is on ServerDatabase is going to be on high end

storage

NAS (Network area Storage)

SAN (Storage area Networks)


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Identifying OS for ORACLE SW version

What kind of OS we need ? Need to follow certification matrix

oracle metalink.www.metalink.oracle.comNeed to choose certified OS

from

Can we install multiple versions

(7,8,8i,9i,10g,11g) of Oracle SW

server?Yes we can

on same
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Single DB vs. Multiple databases

Can we create multiple databases byusing same version of Oracle Software?

Yes we can

One database vs. Multiple databasesNature of applications

DependencySize of the database (maintenance)Application Complexity..


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Instance and Database

Instance will be hosted on server

CPUMEM

PROCESSES

Database (C,R,D files) is located on high endstorage solutions like SAN with fiber optictechnology.Process power and memory for all Databaseoperations are from server resources


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ORACLE INSTANCE BACKGROUND PROCESSESMandate and Optional background process will be

stated when INSTANCE starts

All the running background processes can be viewed@ two different levelsOS LEVEL$echo $ORACLE_SID (Instance Name)

$ps ef | grep $ORACLE_SIDDATABASE LEVEL

- SQL> Select PNAME From v$process Where PNAME

is not null ORDER by PNAME;How to see all the available background process

details

SQL>Select name from v$bgprocess;


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Mandate Background Processes DBWn

DBWn : Writes dirty buffers fromInstanceBuffer Cacheto DBFfiles

SHAREDPOOLDATABASE

USER DATAFILE

Redo buffers


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Mandate Background Processes DBWnDBWn : Writes only dirty buffers that are LRU (Least recentlyUsed buffers) to dbf files and MRU during CKPT

What is the differencebetweenblock(file)andbuffer(memory)

Data BaseBuffer Cache (Memory)

Dbf fileBlocks : (Storage) Default Block Size 8KNon default supported block sizes: 2k,4k,16k,32k


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Types of BuffersinBufferCache

Dirty BuffersFree Buffers

DATABASE BUFFER CACHE

Pinned Buffers


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Types of Buffers in Buffer Cache

Dirty BuffersModified in buffer cache(memory)

that are not yet(storage)

writtentodatafiles

Free BuffersReady to use

Pinned BuffersBuffers that are

in use by Oracle


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DBWn writes when?

Dirty buffers thresholdWhen required free buffers are

available

notDuring graceful/consistent shutdownAny TS status change like (read only,

offline or Tablespace Begin backup..)Checkpoint


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)

Mandate Background Processes LGWR LGWR : Log writer writes change records

redo buffers to redo log filesfrom

SHARED

POOLDATABASE

Current (In use)Active (Required for recoveryInactive (Ready to be current)

Redo log filesLog Switch

Redo buffers


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LGWR writes when

At every commitEvery three secondsWhen 1/3 full of redo log buffersWhen worth of redo records is 1MB

What contains change vectorsChange record is combination of change

vectors

Change vector contains

Scn and Time Stamp of changeTransaction IdCommit details if committed ( scn and timestamp)

Type of operationSegment name and typeChange details


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LGWRServer Process copy redo records from user

memory space (PGA) to redo log buffers for everyDML and DDL

LOG_BUFFER is the parameter to set redo log

buffers size. Min 64k.

Log buffer space (v$session_wait)

wait event(inseconds) indicates insufficient log buffers size

V$system_event - log file switch completion

(event,total_waits, time_waited and average_wait)

Alert log file also records the above event check forcheckpoint not complete

Highly recommended multiplexing


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MandateDBWn

background process CKPT

LRU LRU LRUSHARED POOL


REDO LOGBUFFERS

MRU MRU MRUCKPT

Data723

file 1723 723

723 723

Controlfile Datafile 2 Redo log files


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Mandate background process CHECKPOINT

Checkpoint is a very critical background process to

reduce the instance or media recovery timeCheckpoint wont write any data but in only ensures

marking SCN in Redo, Control file and data filesDuring checkpoint DBWn writes data to dbf files and

marks Redo, control file and data files with scn#Checkpoint position (SCN) in redo is the pointer

where recovery must start fromCheckpoint ensures all the dirty buffers to disk

(LRU & MRU)Checkpoint position is the oldest dirty buffer in thedatabase buffer cache


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Types of checkpointThread checkpoint :(database checkpoint)Database writes to disk all buffers

modified by redo in a specific thread,

occurs during the following situations

Consistent database shutdownAlter system checkpointOnline redo log switchAlter database begin backup


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Types of checkpoint

TS and data file checkpoints:Tablespace checkpoint is with respect to a

particular table space during the status

change like read only, read write, begin

backup. Only for the data files thatbelongs to a TS


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Types of checkpoint

Incremental checkpointsIt is kind of thread checkpoint in order to

avoid large number of blocks at online

redo log switches.DBWn checks every 3 seconds to check

any work to do, if DBWn writes dirtybuffers, it advances the checkpointposition to the control file but not thedata file headers


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Types of checkpoint

Incremental checkpointsIt is kind of thread checkpoint in orderto avoid large number of blocks at

online redo log switches.

DBWn checks every 3 seconds to checkany work to do, if DBWn writes dirty

buffers, it advances the checkpointposition to the control file but not thedata file headers


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Mandate background process SMONSMON : System Monitor

Responsible for Instance crash recovery (ICR)Cleans up temporary segments. For example if

index creation failed it cleans up all the temporary

segments.

What is ICR?

Instance recovery is applying records from redoto dbf files after most recent checkpoint

Information from redo must be transferred todbf to make it permanent and consistent


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SHARED POOL


ICR - SMON

SMONINSTANCE STARTUP AFTER CRASH

CrashRecovery 245

245 Data file 1

245

245

Data file 2

Data file 3

245 - Control file

1.Rollforward2.Rollback (uncommitted txns)3. Recovery done Committed &

un committedCommitted &un committed

245 Undo Data file 1


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Mandate background process PMON

PMON : Processes MonitorResponsible

resources of

for cleaning

adeadprocessesSGA

User processUser process Crash

PMON


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Mandate background process

RECO : Recoverer

RECO Responsible for resolving in-doubttransactionsindistributed

databaseenvironment.Distributed txn

RECO RECO

User


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SQL statements processing inServer

Processes

ORACLE DATABASE

PARSING

DATABASEBUFFER CACHE

1. Syntax check2. Semantic check3.Shared pool check

SHAREDPOOLREDO

BUFFERS

UserProcess

If SPcheck=no

SQL> Select *from employees; soft

harddata file

OPTIMIZERExecution

Row source generation Multiple EPs


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p

Use

SQL statements processing inServer

Processes

ORACLE DATABASE

PARSING

DATABASEBUFFER CACHE

1. Syntax check2. Semantic check3.Shared pool check

SHAREDPOOLUser

ProcessRows u dated

10k 10k 10k

REDOBUFFERSDBWn 20k 20k 20k

If SPcheck=no

SQL> Updatesal=20K fromsalary where

sal=10K

softUndodata file

hardr data file

OPTIMIZERExecution

Row source generation Multiple EPs


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Oracle RAC DBA Training :DBA Technologies

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