An Analogy on the Architectures of Oracle and Animated Living Being

- By SrinivasMaddali 


 To take Oracle more closely than it is to its DBA to Developer, it is necessary that we speak in the terms of audience than in terms of Oracle.

I am a fascinated by the complexities of Human Mind which, I understand, consists of consciousness, Knowledge Base Collected by sensory organs and perceptions historically and also a source to feel at the least 57 identified feelings by me. The reasoning and decision making are also part of that complex gray matter.

By profession I am an Oracle DBA. I know how complex and complicated Oracle internals are and I have been trying to quench my thirst on those internals ever since I started working close with Oracle. I know much less than the unknown vast.

In this presentation an attempt is made to take Oracle close to non-Oracle Life Sciences community.


I dedicate this article to my dad and son and to my wife who are my best friends.

Introduction to Oracle by Oracle

Oracle processes—which include server processes and background processes—and user processes. On almost all systems, the Oracle processes and the user processes are on separate computers.

Background Processes - Oracle Database creates a set of background processes for each instance. The background processes consolidate functions that would otherwise be handled by multiple Oracle Database programs running for each user process. They asynchronously perform I/O and monitor other Oracle Database processes to provide increased parallelism for better performance and reliability.

User processes—sometimes called client processes—are created and maintained to run the software code of an application program (such as an OCI or OCCI program) or an Oracle tool (such as Oracle Enterprise Manager). Most environments have separate machines (laptops, desktops, and so forth) for the client processes. User processes also manage communication with the server process through the program interface, which is described in a later section.

Server Processes - Oracle Database creates server processes to handle requests from connected user processes. A server process communicates with the user process and interacts with Oracle Database to carry out requests from the associated user process. For example, if a user queries some data not already in the database buffers of the SGA, then the associated server process reads the proper data blocks from the datafiles into the SGA. Oracle Database can be configured to vary the number of user processes for each server process. In a dedicated server configuration, a server process handles requests for a single user process. A shared server configuration lets many user processes share a small number of server processes, minimizing the number of server processes and maximizing the use of available system resources.

Instance Memory Structures

Oracle Database creates and uses memory structures for various purposes. For example, memory stores program code being run, data shared among users, and private data areas for each connected user. Two basic memory structures are associated with an Oracle Database:

System Global Area (SGA) is a group of shared memory structures, known as SGA components that contain data and control information for one Oracle Database instance. The SGA is shared by all server and background processes. Examples of data stored in the SGA include cached data blocks and shared SQL areas.

Program Global Areas (PGA) are memory regions that contain data and control information for a server or background process. A PGA is non shared memory created by Oracle Database when a server or background process is started. Access to the PGA is exclusive to the process. Each server process and background process has its own PGA.

The  genesis and gene bundle

Living being has multiple stages in the life, exploded or passed thru with a gotten bundle of genes from its parents in the process of fertilization, Oracle too has multiple stages. Oracle depends on parameter file called


for its gene bundle and has a virtual entity in the memory structures of a host server in nomount - only instance is conceived

mount – the conception is ready for physical association with data and redo log files

open restricted – ready for adulthood but under protected mode

migrate – to upgrade its capabilities takes classes, let me say, and undergoes metamorphosis

open – ready to show the world its universal form

Oracle becomes a perceivable entity ready to be associated with physical structures which it can read and write to when in MOUNT stage like a baby that is there, at the same time a helpless reading ‘controlfiles’ and trying to understand thru that bundle of genes  it future shape and size and ability to grow. YOU need to do everything for it, be it repairs or maintenance or throw it Open to Free World.

When you open that ‘Baby’ RESTRICTED to a family of DBA nobody else is allowed to communicate with that Baby, as it is in a kind of monitored or may be quarantined or might have needed an incubated environment for a specific purpose.

Throw her OPEN – and behold the Universal Form of that Oracle Instances associated with the Database serving multitude to translate their dreams of Business. Never tired and restless.

Attachment in Detachment Architectures

Oracle never allows any user to use HER by himself or herself. Let me know and you are severed. It is so complex and complicated a relation. Believe it or not, she knows what to serve you and what not to. She has her own rules and then you need tell Her too your own rules as the owner or buyer of the space in Public Storage.

Like any other bundle of Software Oracle is FRAGILE and hence would not allow any body to directly be in touch with her. ‘Don’t touch me’ – Lady Oracle warns you – when you are fascinated and feel like having a warm hug and cool kiss.

The User Request Process submits a request for information service then


1.   Oracle provides a DEDICATED server process for each User that wants to her services if one-on-one relation with Her is requested.

2.   Oracle provides a SHARED server process when you ask for a Royal Welcome for your community to the rendezvous with Lady Oracle each user’s request is connected to a dispatcher process and that process submits that User Request to any of the server processes that is in the free queue to serve a User. This is a SHARED environmental architecture and Oracle provides a pool of server processes to extend Royal Welcome to Her presence for service.

Look at that, every user is attached to a Oracle Server Process (DEDICATED or SHARED) but is DETACHED with Oracle. Everybody enjoys her service but never her. She is so complicated and complex Gorgeous Lady.

She reminds me of John Keats’ melodramatic situation when he was penning his most famous ode on Grecian Urn.

Musculoskeletal System and Supporting System in Animated Forms compared to Oracle

Like the skeleton and muscles wrapped up into a body covered by the skin to give a shape to the form which is visible to the naked eye, Oracle has its skeletal structures described as

1.   Redo log files

2.   data files

Archived log files are optional structures, depending upon the desire of the creator (YOU) of the instance/database to re-generate the database when it is lost or you want to roll that back into the past.

While a rollback is not possible for a body mass with a form and life with all its vital characters, Oracle permits to roll backwards or forwards basing on a given/saved image at various stages in the linear time scale.

These skeletal structures are wrapped around by the background processes and server processes that provide soft and hard locks to keep them together in a skin sack provided by these background and foreground processes that convert the potential energy of Oracle into a kinetic form of that unique database, an entity you give a name and you interact with.

Time is a cyclical concept in Indian thought and philosophy not linear as has been thought of in western philosophy – time started with ‘big bang’.  Thus ‘reborn’ philosophy too.

Oracle also believes with some modifications but not leaving the basic time cycle philosophy and hence we see restartable images, recoverable images and renamed restartable images and increasing portability.

My Belief on LIFE and its association with a Body compared to Oracle Instance, Data files and Control file

LIFE expresses itself thru a FORM. Otherwise LIFE remain a potential force only. This is my belief. I am not able to prove this. A FORM is declared DEAD, in 2 cases. If the life feels that the form can not hold or is not fit enough and if the FORM is not able to hold within itself the potential force LIFE.

What determines the expression of LIFE thru which FORM is not known to me?

Oracle Instance when associated with data files and redo log files it gains the form of an Oracle Database. But which data files are to be associated with that potential force Oracle is determined by the control files.

Motor Nervous System compared to Control Files

When Life starts using the form the activated nervous system identifies all the limbs and other parts of the body. I remember V.S.Ramachandran discussing in his ‘A Brief Tour of human Consciousness’ says that the mind can carry phantom images of the body parts and to experience the reality of loss of any limbs the brain is to be trained. As long as the old image is not erased from the memory of brain, even the amputated parts of the body are still seen and try to use them and feel the pain of it too.

We need to train that part of the brain that it has no more that amputated part of the body.

Oracle Control files is a kind of that part of the motor nervous system of parietal lobe.

Oracle Control files determines which Instance is to be associated with which set of data files and redo log files. They also determine whether the body is in synch or not by tracking certain vital information like System Change Numbers (SCN) and other required information like

1.   Name of the database

2.   database creation and reset log information

3.   archive log information if the option is enabled

4.   redo threads

5.   log records and each SCN for each log

6.   database block corruption details

7.   database id

8.   tablespace names and names of the associated data files

9.   RMAN catalog

Unless proper mechanism to alter contents of the control file is implemented, Oracle goes on complaining and would not allow you to OPEN the database. Oracle, on its own may take off line one or more data files that are associated with the tablespace or a tablespace. In such circumstances those data files or tablespace are to be recovered or to be dropped from within the database. Check it out, it is like training the brain to accept the amputated part of the body.

Supporting Systems for Involuntary Activities in Life Forms compared to Oracle

Circulatory, respiratory, digestive and excretory systems Life Forms have, Oracle has Server and Background Processes.

Gathering Food is an essential part of the Life. This process of gathering food has been sophisticated by the process of evolution that modified multiple body parts including the process of reasoning and decision making that can help gather food.

The eyes, ears, mouth, fore and hind limbs are all to fulfil that process of gathering food. Communication serves not only to fulfil the process of gathering food but also to feel a sense of security with a sense of belonging ness and expression/s.

Oracle has SERVER processes that gather data from the source files. All these Server Processes are foreground processes and there are background processes to match circulatory,  respiratory,  digestive and excretory systems. There are multiple background processes that process data and ultimately provide that data to those server processes that communicate with the user process to provide the data as has been asked or modify data as has been suggested.

They are

1.   LGWR - Log Writer – This background process writes sequentially batches of modified entries in the memory structures redo buffers for one or more transactions to the online redo log files. Multiple LGWR processes are not allowed as of now by Oracle.

2.   ARCn – Archiver - Optional background process – that generates the archived log files by saving online redo log files to arched log file destination. This process is active only when the database is in ARCHIVELOG mode. Multiple ARC processes are allowed by Oracle with a maximum of 30 set for the instance using LOG_ARCHIVE_MAX_PROCESSES.

3.   DBWn – DB Writer - This background process is to write back to the source (data files) all the changes impacted (that live in the memory buffer cache) to the data as requested by the User/Owner of the data. The initialization parameter DB_WRITER_PROCESSES specifies the number of DBWn processes. The maximum number of DBWn processes is 20. If it is not specified by the user during startup, Oracle determines how to set DB_WRITER_PROCESSES based on the number of CPUs and processor groups. Leave that to default and YOU are fine.

4.   SMON – System Monitor- background process takes care of the instance recovery when a crash recovery is to be made by Oracle.

5.   PMON –Process Monitor - background process takes care of the of the process recovery in case of a process crash. The process monitor (PMON) performs process recovery when a user process fails. PMON is responsible for cleaning up the database buffer cache and freeing resources that the user process was using. For example, it resets the status of the active transaction table, releases locks, and removes the process ID from the list of active processes. PMON periodically checks the status of dispatcher and server processes, and restarts any that have stopped running (but not any that Oracle has terminated intentionally). PMON also registers information about the instance and dispatcher processes with the network listener. SMON and PMON processes check regularly to see whether it is needed and can be called if another process detects the need for it.

6.   RECO – Recoverer Process - this background process is used with the distributed database configuration that automatically resolves failures involving distributed transactions. The RECO process of a node automatically connects to other databases involved in an in-doubt distributed transaction. When the RECO process reestablishes a connection between involved database servers, it automatically resolves all in-doubt transactions, removing from each database's pending transaction table any rows that correspond to the resolved in-doubt transactions. If the RECO process fails to connect with a remote server, RECO automatically tries to connect again after a timed interval. However, RECO waits an increasing amount of time (growing exponentially) before it attempts another connection. The RECO process is present only if the instance permits distributed transactions. The number of concurrent distributed transactions is not limited.

7.   J000 and CJQ0 processes - Job Queue Processes - Job queue processes are used for batch processing. They run user jobs. They can be viewed as a scheduler service that can be used to schedule jobs as PL/SQL statements or procedures on an Oracle instance. Given a start date and an interval, the job queue processes try to run the job at the next occurrence of the interval. Job queue processes are managed dynamically. This allows job queue clients to use more job queue processes when required. The resources used by the new processes are released when they are idle. Dynamic job queue processes can run a large number of jobs concurrently at a given interval. The job queue processes run user jobs as they are assigned by the CJQ process. Here's what happens: (a) the coordinator process, named CJQ0, periodically selects jobs that need to be run from the system JOB$ table. New jobs selected are ordered by time. (b) The CJQ0 process dynamically spawns job queue slave processes (J000…J999) to run the jobs. (c) The job queue process runs one of the jobs that was selected by the CJQ process for execution. The processes run one job at a time. (d) After the process finishes execution of a single job, it polls for more jobs. If no jobs are scheduled for execution, then it enters a sleep state, from which it wakes up at periodic intervals and polls for more jobs. If the process does not find any new jobs, then it aborts after a preset interval. The initialization parameter JOB_QUEUE_PROCESSES represents the maximum number of job queue processes that can concurrently run on an instance. However, clients should not assume that all job queue processes are available for job execution.

8.   QMNn - Queue Monitor Processes - The queue monitor process is an optional background process for Oracle Streams Advanced Queuing, which monitors the message queues. You can configure up to 10 queue monitor processes. These processes, like the job queue processes, are different from other Oracle background processes in that process failure does not cause the instance to fail.

9.   MMON - Memory Monitor - performs various manageability-related background tasks, such as issuing alerts whenever a given metrics violates its threshold value. Taking snapshots by spawning additional process (MMON slaves). Capturing statistics value for SQL objects which have been recently modified. MMON background slave (m000) processes are identified separately. The memory monitor (MMON) process was introduced in 10g and is associated with the Automatic Workload Repository new features used for automatic problem detection and self-tuning. MMON writes out the required statistics for AWR on a scheduled basis.

10.               MMNL - Memory Monitor Light - performs frequent and light-weight manageability-related tasks, such as session history capture and metrics computation. The Memory Monitor Light (MMNL) process is a new process in 10g which works with the Automatic Workload Repository new features (AWR) to write out full statistics buffers to disk as needed.

11.               MMAN -Memory Manager - is used for internal database tasks. The Automatic Shared Memory Management feature uses a new background process named Memory Manager (MMAN). MMAN serves as the SGA Memory Broker and coordinates the sizing of the memory components. The SGA Memory Broker keeps track of the sizes of the components and pending resize operations.

12.               RBAL coordinates rebalance activity for disk groups in an Automatic Storage Management instance. It performs a global open on Automatic Storage Management disks. ORBn performs the actual rebalance data extent movements in an Automatic Storage Management instance. There can be many of these at a time, called ORB0, ORB1, and so forth.

13.               OSMB is present in a database instance using an Automatic Storage Management disk group. It communicates with the Automatic Storage Management instance.

14.               PSPn - process spawner - spawns Oracle processes.

15.               RVWR - Recovery Writer ( RVWR) introduced which is responsible for writing flashback logs which stores pre-image(s) of data blocks (1) One can use Flashback Database to back out changes that (a). Have resulted in logical data corruptions. (b) Are a result of user error. (c) This feature is not applicable for recovering the database in case of media failure. (d) The time required for flashbacking a database to a specific time in past is DIRECTLY PROPORTIONAL to the number of changes made and not on the size of the database.

16.               CTWR - This is a new process Change Tracking Writer (CTWR) which works with the new block changed tracking features in 10g for fast RMAN incremental backups.

17.               ARBx - These processes are managed by the RBAL process and are used to do the actual rebalancing of ASM controlled disk resources. The number of ARBx processes invoked is directly influenced by the asm_power_limit parameter.

18.               ASMB - The ASMB process is used to provide information to and from the Cluster Synchronization Services used by ASM to manage the disk resources. It is also used to update statistics and provide a heartbeat mechanism.

Nervous System - Reasoning and Decision Making compared to System Global Area  

The bundle of genes provided by the initialization parameter file that spawns system global area. It is true that Brain which is the center of the activity for all decision making and reasoning and repository of the ciphered knowledge and thus consciousness.

The scientific community is still trying to understand the brain its functions. There us no hard disk like to store data which is limited by some capacity in the brain. The ability of the brain is unlimited. The capacity of the brain to store data is unlimited.

Let this be clear that I am not a neurological sciences student but a reader.

The attempt, which I am making in this part of the article, is not to map at one to one with Oracle memory structures. It is just a kind of analogy. I beg every one not to construe nor misunderstand, but enjoy or do not like this let me know or ignore this.

CPU and Memory are the structures that OS allows Oracle to share with on the board.

Every system can survive only when there is a host. Every server is a host, on which Oracle is installed. Oracle uses the resources that are made available by the host.

Some time back I read on some pages of IBM

“In a multitasking environment there is often a requirement to synchronize the execution of various tasks or ensure one process has been completed before another begins. This requirement is facilitated by the use of a software switch known as a Semaphore or a Flag. The function of this is to work in much the same way a railway signal would; only allowing one train on the track at a time. A semaphore timeout is where the railway signal has been set in one state too long, maybe because the train has broken down.” These are some of the Basic UNIX Operating System Kernel Shared Memory Structure resources Oracle uses to create its Brain (Its Memory Structures and Background Processes + Program Global Area that make fully functional Oracle Instance). On Windows Operating System the resources are provided by the threads. Much more discussion on the architectural differences may not be relevant here at all.

The brain mapping broadly consists of as has been taught by my son: