Oracle Databasae Architecture

 

Oracle Databasae Architecture

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Introduction

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An oracle databse is a collection of data treated as a unit,The purpose of database is to store and retrieve related information, a database server is the key to solving the problems of information management,in general , aserver reliably manages large amount of data in a multiuser environmemnt so that many users can concurrently access the same data, all this is accomplished while delivering high performance.A database server also prevents unauthorized acess and provides efficient solution for failure recovery

     Oracle database is the first database designed for enterprise grid computing, the most flexible and cost efective way to manage information and applications. Enterprise grid computing create large pools of industry standard ,modular storage and servers,with this architecture,each new system can be rapidly provisoned from the pool of components there is no need for peak workloads,because capacity can be added or reallocated from the resources pools as needed Defines the components of database software database is the to store data in terms of files database can be used in these sectors

Banking

Insurance

Oil

Retails

Real estate

Airlines

Payment gateways

Govt Sectors

private setors

   The Database has a logical structures and physical structures.Because the physical and logical structures are separate,the physical storage of data can be managed without affecting the acess to logical storage structures,Oracle is an RDBMS (Relational database management systems),The oracle RDBMS stores data logically in the form of tablespaces and physically in the form of data files,the oracle database architecture can be described in terms of logical and physical structures,The advantage of separating the logical and physical structure is that the physical storage structure can be changed without affecting the logical structures.

Physical structure: The physical layer of the database consists of three types of files

One or more datafiles

two or more redolog files

one or more controlfiles

DataFiles(.dbf files): Data files stores the information contained in the database.one can have as few as one datafiles or as many as hundreds of data files.The information for a single table can span many datafiles or many tables can share a set of datafiles,the number of data files that can be configured is limited by the oracle parameter db_files, to stores permanent data

Redo Log Files(.log): Oracle maintains logs of all the transaction against the database,These transactions are recoreded in files called online redo log files(Redo logs) The main purpose of the redo log files is to hold information as recovery in the event of system failure,redo log stores a log of all changes made to the database the redolog files must perform well and be protected against hardware failures (through software or hardware fault tolerance).if redolog information is lost,one cannot recover the system when a transcation occurs in the database,it is entered in the redo log buffers,while the data blocks affected by the transactions are not immediately written to disk,in an oracle database there are at atleast three or more redolog files,oracle  writes to redolog files in a cyclical order i.e after the first log file is filled ,it writes to the second log file,untill that one is filled .when all the redo log files have been filled,it returns to the first log file and begin overwrite its content with new transaction data.note if the database is running in ARCHIVELOG mode,the database will make a copy of the online redolog files before overwriting them

Control Files (.ctl): control files record control information about all of the files with in the database,control files contain information used to start an instance, such  as the location of the datafiles and redologfiles ,oracle needs this information to start the database instance.control files must be protected,oracle provides a mechanism for storing multiple copies of control files,These multiple copies are stored on as separate disks to minimize the potential damage due to disk failure,the names of the database conntrol files are specified via the CONTROL_FILES initilization parameter. The control file is small binary file the contents of the control files are database name,time stamp creation of database,location of datafiles and redo log files,

checkpoint information of every record (dml)with scn number (system change number)

The parameter file defines the characterstics of an oracle instance.for example ,it contains parameters that size some of the memory structures in the SGA

The password file authenticates user privileged to start up and shutdown an oracle instance

The archived redo log files are offline copies of the redolog files that may be necessary to recover from media failures

sql> select name,value from v$ parameter;

sql> select name,bytes,1024/1024,autoextensible from dba_data_files;

Instance(service )startup ,shutdown

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A database instance(also save as server) is set of memory structures and background process that access a set of database files,constitutes of memory structure and background process every database has one or more instancess,database running in one server has one instance,if multiple servers (RAC) will have mltiple instances

Instance = memory+Bg process

eg: host1 prod(dbname-sid)prod(instance)

sid: system identifier is the instance name

Memory Structure is divided into SGA and PGA

SGA: The SGA is also called the shared global area it is used to store database information that is shared by database process,it contains data and control information for the oracle server  and is allocated in the virtual memory of the computer where oracle resides, oracle uses an area of shared memory called the shared global area(SGA) The SGA is a shared memory region that contains data and control information for one oracle instance oracle allocates the SGA when an instance starts and de-allocates it when the instance shutdowns,every instance has the sga ,the entire SGA should be large as possible to increase the system performance and to reduce disk i/o.

From 11g ,oracle introduced Automatic memory management (AMM) using two parameter control instance memory with

SGA is set with parameter  SGA_MAX_SIZE

sql> show parameter sga_max_size (from 11g is et to zero -amm is enabled)

Memory_max_target

memory_target

RAM(64g)> memeory_max_target(60g)>=memory_target(35g-dynamic)>=sga+pga

with in the size of memory_target,oracle server distributes across sga and pga

If memory_target is set to non zero value with in the size of memory_max_target 

If memory _target>0 (AMM is enabled -->without restart dynamic)

memory_max_target>0 (static--need restart)

memory_target=0(AMM is disabled), then dba ha s manually allocate memory for sga and pga

The information is stored in the SGA is divided into three memory structures

1)Database buffer cache 

2)Redo Log buffer

3)Shared Pool

1)Database buffers cache: The database buffer stores the most recently used blocks of data.The set of database buffers in an instance is the database buffer cache,the  buffer cache contains modified as well as unmodified blocks,because the most recently and most frequently used data is kept in memory.it improves the performance of system by reducing the i/o operations

2)Redo Log Buffer: The redo log buffer stores redo entries .these are log of changes made to the database in database buffer cache.The redo entries stored in the redo log buffers are written to an online redo log,an online redo log is a set of two or more files that record all the changes made to oracle data files and control files.

Data buffer cache: holds modified as well as unmodified blocsks most recently used (MRU) willbe kept and Least recently used (LRU) willbe written into files

oracle uses MRU and LRU algorithm

sql> show parameter db_cache_size

0 - amm is enabled

Log Buffer cache: Holds log of changes made against to database for recovery purpose in the event of system failure every 1/3 or 3 secs fills will write in online redolog files

sql> show parameter log_buffer

 1m /6m max value -recommended

3)Shared Pool : The shared pool is used to store the most recently execeuted sql and plsql statements and the most recently used data definition

it consits of two key performance related memory structures

Library cache: Library cache stores information about the most recently used sql and pl/sql statements,enables the sharing of commonly used statements,it is 

managed by the least recently used (LRU) algorithm

Data dictionary cache: The data dictionary cache is a collection of the most recently used definitions in the database,holds dictionary inforamtion of tables,indexes,users,permissions

sql>show parameter shared_pool_size

0 (If AMM is enabled) also we can give fixed value with in the size of memory_target

Program Global Area:

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 PGA is a memory buffer that contains data and control inforamtion for a server process,A server process is a process that services a client reqeuests.A PGA is created  by oracle when a server process is started.theinformation in a PGA depends on the oracle configuration,The PGA area is non shared area of memory created by oracle when a server process is started ,the basic difference between SGA and PGA is PGA is cannot shared between multiple processes in the sense that is used only for requirements of a particular process whereas the SGA is used for the whole instance and it is shared.

Back ground process

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Few background process writes or read into file and memory, the trace files are only created whenthere is any problem,some of the background process are

PMON: PMON stand Process monitor and this is database backround process cleans up failed user process also relases dead locks, cleaning up the cache and freeing resorces that the process was using (its effect can be seen when a proces holding a lock is killed

 $ ps -ef |grep pmon

SMON: SMON stands for system monitor and this is database background process performs instance receovery at the start of the database,SMON also cleans up temporary segments that are no longer in use and recovers dead transcations skippedduring crash and instance recovcery because of file read or offline errors .it coalesces combines contiguos free extents into large free extents 

 $ ps - ef |grep smon

system crash--->redologfiles---->smon--.startup---->recovery changes--->datafiles

LGWR:LGWR stands for Log writer background process manages the writing of the contents of the redo log buffer to the online redolog files,LGWR writes the log entries in the batches form,the redo log buffers entries always contain the most upto date status of the database note LGWR is the only one process that writes to the online redo log files and the only one that directly reads the redo log buffer during to the database  normal database operation, writes from redolog buffer to online redo log files every 1/3 rd or 3 sec fills

$ ps -ef | grep lgwr

DBWR:DBWR stand for database writer background process is responsible for managing the contents of the datablock buffer cache and dictionary cache,DBWR  performs batch writes of changed block,DBWR doest not need to write blocks blocks when a transcation commits,can have upto 20 process with parameter db_writer_process,DBWriter writes from buffer cache to data files in batch form not on every commit

$ ps - ef | grep dbwr

CKPT: CKPT stands for check point transaction all modified information in database buffer in the sga is written to the datfiles by a database write process (DBWR) This event indicates checkpoint,the checkpoint processis responsible for signalling DBWR at checkpoints and updating all the datafiles and controlfiles of the database, onec the DBWR writes in to the datafiles then signal to CKPT a checkpint process occurs,then the ckpt process update in a datafile header and control file with the 

SCN number (system change nmber for every record)

$ ps - ef | grep ckpt

number of instances running on a server

using ps - ef |grep smon

ps -ef |grep pmon 

ARCHIVER(ARCH): The archiver process reads the redo log files once oracle has filled them and writes a copy of the used redo log files to the specified archive log destinations actually ,for most databases,the ARCH has no effect on the overall system performance

MMAN: MMAN dynamically adjust the sizes of the SGA components ,it is a new process added to oracle 10 g as part of automatic shared memory management

FMON: The database communicates with the mapping libararies provided by the storage vendors through an external non oracle database process that is spawned by  a background process called FMON,FMON is responsible for managing and mapping information 

LMON:LMON stands for Lock manager process lock monitor is an oracle background process created when you start a database instance in RAC mode the LMON process manages global locks and resources,it is also called as global enqueue service monitor,it monitor all instances in the cluster primarily for dictionary cache locks and dead locks on dead locks sensitive equeues and resources,LMON also provides cluster group services

MMON: the oracle 10 g background process to collect statastics for the automatic workload repository (AWR)

MMNL:This process performs frequent and lightweight manageability relatedtasks such as session history capture and metrics computation

WMON: The Wake up monitorprocess

RVWR: Recovery Writer oracle starts the recovery writer (RVWR)process to write the flashback data from the flashback buffer to the flash back logs

CTWR:(change tracking writer) oracle tracks the physcical location of database changes in a new file called the change tracking file.oracle backup utility the recovery manager RMAN uses the change tracking file to determine which data blocks to read during an incremental backup,making the incremental backups faster by avoiding reading entire data files.

DMON:Dataguard

DIAG: the diagnosibility process DIAG runs oracle bug commands  and triggers  diagnostic dumps as part of the new ADR(automatic diagnostic repository )feature which is replacement and major enhancement for the much reviled RDA

SMCO: The space management cordinator and slaves perform space allocation and reclamation

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vi editor in linux

 

vi editor in linux

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vi editor introduction

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vi editor is a visual text editor ,the default editor comes with unix operating system,unix vi editor is a full screen editor ,two modes of operation command mode and insert mode ,vi editor is free and open source ,vi uses less amount of system resources,vi supports all programming languages and differnt file formats also,vi is interactive text editor that is display oriented,using vi you can insert text anywhere in the file very easily.

To launch the vi editor open the terminal 

vi <filename_new> or <filename_existing>

vi chaitanya.txt

vi editor commands

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i----->insert at cursor (goesinto insert mode)

a----->writes after cursor (goes into insert mode)(append after cursor)

A------>write at the end of the line (goes into insert mode)(append after line)

esc---->terminate insert mode

u------>undo last change

U------>undo all changes to the entire line

o------> open a new line (goes into insert mode)

O ------> open a new line before current line

Deleting Text

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dd------>delete line

3dd-----> delete 3 lines

D------->delete contents of line after the cursor

c------->delete contents of line after the cursor and insert  new text .press esc key to end

d$ -----> deletes from the cursor to the end of the line

ndw ----->deletes the next n words starting with current

ndb -----> deletes the previous n words starting with current

ndd -----> deletes n lines begginning with current line ,suppose we want to delete 100 lines then 100dd

nmd ------>deletes lines n through m

Insertion

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dw------>delete word

4dw------>delete 4 words

cw------->change word

x-------->delete character at the cursor

r-------> replace character

R-------> overwrite characters from cursor onward

s------->substite one character under cursor continue to insert

S------->substitute entire line and begin to insert at the begining of the line

~------> change case of individual character

:r ----->file reads file and inserts it after current line

:nr ----> file reads file and inserts it after line n

p -----> put after the position or after the line

P ------> put before the positionor before the line

Moving cursor with in a line

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K ------>move cursor up

J------->move cursor down

h------->move cursor left

l------->move cursor right

w ------> move to the next word

W -------> move to the next blank delimited word

E--------> move to the end of blank delimited word

O or | ----> move to the beginning of the line

n| ------> moves to the column n in the current line

$ -------> move to the end of the line

1G -----> move to the firstline of file

G -------> move to the last line of the file

nG ------> move to the nth line of the file suppos eyou want to move to 100 th line then 100G

n ------> move to the n th line of the file

H ------> move to top of screen

nH -----> moves to nth line from the top of the screen

M ------> move to middle screen

Searching for Strings

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/string -----> search forward for string like error

?string ----> search bak for string

n ------> search for next instance of string

N ------> search for previous instance of string

% ------> search to begining of balancing(){} []

?str ----> finds in reverse for str

/fmw_home  -----> search forward for fmw_home in the file

?fmw_home ------> search backward for fmw_home in the file

n ------>repeat previous search

N ------> repeat search in opposite direction

/.? -----> repeat search forward or backward 

Replace or substitution

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 The search and replace function is accomplished with the :s command. it is commonly used in combination with ranges or the  :g command(below)

:s/pattern/string/flags replace pattern with string accordingto flags

g Flag ---> repalce all occurances of pattern

c Flag ----> Confirm replaces

& Repeat last :s command

it can be used like this also 

:s,pattern,string,flags

:s^pattern^string^flags

:s^/oracle^/java^g  ----> This will replace /oracle with /java every where in the file 

s,^a,^b,g -----> this will replace  ^a with  ^b everywhere in the file

Saving and closing the File

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shift++zz ----->save the file and quit

:w -----> save the file but keep it open

:w! -----> saves current file overriding normal checks but doesnt exit

:q ------> quit without saving

:q! -----> quits vi and without saving ifyou have done some mistake and want to quiy without making any changes

:e! ----->edits file discarding any unsaved changes(starts over)

:we! ----> saves and continues to edit current file

:wq-------> save the file and quit

Yanking Text

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yy -----> yank the current line

:y -----> yank the current line

nyy or nY -----> places n lines in the buffer -copies

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