Server Architecture on UNIX and NT

Subject:	Server Architecture on UNIX and NT
	Doc ID:	Note:48681.1	Type:	BULLETIN
	Last Revision Date:	26-MAY-2005	Status:	PUBLISHED

Oracle Server Architecture on UNIX and NT

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This article concentrates on the way Oracle works on UNIX and Windows NT,

but other platforms will be mentioned.

1.  What are the Oracle background processes/threads?

2.  What are the differences between background processes on UNIX and NT?

3.  How are the background processes/threads implemented on UNIX and NT?

4.  What are the limits on file and database size on UNIX and NT?

5.  How does Oracle use memory on UNIX and NT?

6.  How does Oracle bypass the filesystem cache on UNIX and NT?

7.  How does Oracle utilise the features and characteristics of SMP systems?

8.  How does Oracle utilise the features and characteristics of MPP systems?

9.  How does Oracle work on clustered systems?

10. The different SQL*Net protocol adapters and their environments.

11. How Oracle environment variables are set on different systems. 

12. How is the ORACLE_HOME location chosen on different systems?

13. What are the limitations on choosing ORACLE_SID?

14. How are operating system and Oracle libraries used on UNIX and NT?

15. Accounts and groups used for Oracle installation and administration.

16. Finding out and setting the size of the System Global Area (SGA).

17. How are different releases of Oracle distinguished on UNIX and NT?

18. What is meant by the terms "upgrade" and "migrate"?

19. What are the routes for transporting data between different platforms?

20. What is the difference between a server option and a server cartridge?

1. What are the Oracle background processes/threads?

These are the processes (on UNIX) or the threads within a process (on NT)

which manage the Oracle RDBMS. Some must always be running for the server

to be available; others are optional on all platforms; and some are optional

and specific to certain platforms.

A = Must always be running

O = Optional on all platforms

P = Optional and specific to a platform

DBWR (A) - the database writer

LGWR (A) - the log writer

PMON (A) - the process monitor

SMON (A) - the system monitor

CKPT (O) - the checkpoint process (or thread)

ARCH (O) - the archive process (or thread)

RECO (O) - the recoverer process (or thread)

SNPnnn (P) - snapshot process

LCKnnn (P) - inter-instance locking processes

Snnn (P) - shared server process in multi-threaded server

Dnnn (P) - dispatcher process in multi-threaded server

WMON (P) - wakeup monitor process

QMNn (P) - AQ Time Manager

TRWR (P) - Trace Writer

LMON (P) - Lock Manager Monitor

LMD0 (P) - Lock Manager Daemon

MMAN (O) - Memory Manager

RBAL (O) - Rebalances ASM disk resources

ASMB (O) - Communicates to and from Cluster Synchronization Services (ASM)

RVRW (O) - Recovery Writer (associated with Flashback Database)

MMNLL(O) - Memory Monitor Light

ARBx (O) - Processes managed by RBAL

CTWR (O) - Change Tracking Writer (RMAN fast incremental backup)

DMON (O) - Data Guard Broker

2. What are the differences between background processes/threads on UNIX and NT?

There is no difference between the functions, the background processes or

threads fulfil. For example, the log writer does exactly the same, in Oracle

terms, on UNIX and NT. The way they are implemented, however, is different.

3. How are the background processes/threads implemented on UNIX and NT?

On UNIX, a separate operating system process is created to run each of the

background functions listed above. On NT, they are run as different threads

within the same process.

4.  What are the limits on file and database size on different platforms?

On UNIX, block sizes usually vary between 2-8K, although larger than 8K is

possible. Maximum database file size is 2Gb on most 32-bit UNIX platforms,

though some (AIX, Solaris and HP/UX) now support a larger maximum, usually 32Gb.

On NT, there are only 4 million blocks per datafile, because there are 32 bits

available for block# and file#. So to support 256 (2**8) files/database

requires 8 bits for the file number, leaving 24 bits for the block number;

this gives 2**24 or 16 million blocks per file. However, if 1024 (2**10) files

are to be supported, only 222 or 4 million blocks/file is possible. So, 1024

files/database allows a maximum 4 million blocks/file. Note that the total

maximum possible capacity of the database remains the same regardless of the

way the bits are split up.

5. How does Oracle use memory on UNIX and NT?

On UNIX, the background processes attach to shared memory, one of the standard

interprocess communication methods on UNIX. On NT, this is not necessary, as

the Oracle threads all share the same virtual address space anyway.

6.  How does Oracle bypass the filesystem cache on UNIX and NT?

On UNIX, Oracle opens files using the O_SYNC flag to bypass the filesystem

buffer cache. In the current Win32 API, the equivalent flags are

FILE_FLAG_NO_BUFFERING and FILE_FLAG_WRITE_THROUGH. The goal in both cases is

the same; to ensure that data has been posted to disk before assuming that the

write has been successful.

7.  How does Oracle utilise the features and characteristics of SMP systems?

Oracle utilises as many CPUs as are available. This is completely transparent

to the Oracle user or application developer. The only init.ora parameter that

may need setting is SPIN_COUNT, to influence how long a process will wait for

a latch to become available. Before and after tests should be always be carried

carried out to determine the effects of setting this parameter on database

performance. 

See Note 30832.1 for details of SPIN_COUNT.

8.  How does Oracle utilise the features and characteristics of MPP systems?

Oracle Parallel Server (OPS) is available for MPP systems from all the major

vendors. The way in which it works varies between platforms; for example,

whether the vendor's lock manager is used, or an Oracle-supplied one.

9.  How does Oracle work on clustered systems?

As on MPP systems, this is very platform-specific, ranging from the more

traditional type of VAX/OpenVMS or Alpha/OpenVMS clusters to emerging

technologies such as NT clusters. Usually, OPS will be used, to take

advantage of the independent processing capability of the different cluster

nodes.

The Oracle Fail Safe product is available for selected two-node NT clusters

running MS Cluster Server. If one of the nodes fails, the other can take over

its workload. This product is not related to OPS.

10. The different types of SQL*Net protocol adapters and their environments.

The major protocol adapter for use with SQL*Net is TCP/IP. This is true for

all platforms. Other adapters that are supplied with the Oracle server depend

on the platform. For example, adapters that can be used on NT are Named Pipes

(Microsoft networking), SPX (for use in Novell environments), TCP/IP, Bequeath

(for local databases) and IPC (for local processes). 

On UNIX, TCP/IP, SPX, Bequeath and IPC are again supported. Oracle on many

UNIX platforms also includes adapters for the DECnet protocol and IBM LU6.2

protocol. Note that no DECnet protocol adapter is shipped with Oracle8.

The most important point about protocol adapters is that no protocol adapter

should be installed if the underlying protocol is not present on the machine,

e.g. do not install the IPX adapter if you are not using the IPX/SPX protocol.

Failure to observe this can lead to serious problems on UNIX.

11. How are Oracle environment variables set on different systems?

The variables used by Oracle for the SID, ORACLE_HOME and so on are the same

on different platforms, but stored differently. On OpenVMS, logical names are

used; on UNIX and NT, environment variables. UNIX environment variables are

set differently depending on whether the C-shell or Bourne/Korn shell is in

use.

On NT, environment variables may be set in one of three ways:

1. In a similar way to Bourne or Korn environment variables on UNIX. For

   example, in a command window, enter:

   C:\>set ORACLE_SID=ORC8

   Such a setting only has effect in the command window where it was made.

2. In Start > Settings > Control Panel > System > Environment

   by entering either a System or User Variable name and value. This updates

   the Registry.

3. By running the Registry Editor (REGEDT32) directly, and entering a new

   Key Value (variable name) and Value Data (value) in the appropriate

   subtree. Care should always be taken when editing the registry directly.

12. How is the ORACLE_HOME location chosen on different systems?

On most systems, including UNIX, the value of ORACLE_HOME is chosen by the

DBA doing the install, based on knowledge of available disk space. On NT,

the Oracle Installer offers as default the disk with the greatest amount of

free space. This can be over-ridden by the DBA doing the install.

13. What are the limitations on choosing ORACLE_SID?

The SID should consist of four or fewer alphanumeric characters. This is to

avoid problems with filename length restrictions on some platforms, e.g. the

8.3 restriction on DOS, which is still present on NT if using DOS-style names

(which Oracle requires). So the initialisation file for a database called ORCL

will be called initORCL.ora, representing the longest possible filename.

14. How are operating system and Oracle libraries used on different systems?

On UNIX, there is a general library for all products, plus separate libraries

for each product under that product's directory. These directories contain a

mixture of objects (which have a .o suffix) and archive libraries (which have a

.a suffix). Before a product can be used, it must be built, using the make

utility. This can lead to very large executables, as the relevant libraries

have to be built in to the image. For example, a very small program such as

one which simply prints hello may be 16K in size. This will not apply

if shared libraries are used.

On NT, executables tend to be much smaller, because of the Windows usage of

dynamic link libraries (DLLs). These are very similar to shared libraries on

UNIX, or shareable images on OpenVMS. They are dynamically linked with the

executable at runtime.

15. What accounts and groups are used for Oracle installation?

On UNIX, a dba group (the default name is "dba") and Oracle user (no default,

a good choice is something like "oracle" or "ora7") are required. Oracle cannot

be installed by the root user.

On NT, the account used for Oracle installation and maintenance must either be

the Administrator account, or an account in the Administrators group.

16. Finding out the size of the System Global Area (SGA).

The size of the SGA may be obtained as follows:

(a) On startup.

(b) By entering SHOW SGA when connected internal to Server Manager.

Both of these show something like:

Total System Global Area       4830836 bytes

Fixed Size                       46596 bytes

Variable Size                  3948656 bytes

Database Buffers                819200 bytes

Redo Buffers                     16384 bytes

17. How are different releases of Oracle distinguished on UNIX and NT?

On UNIX, there can be as many installations of Oracle as the machine's

resources will allow. They are distinguished by the environment variables

ORACLE_HOME and ORACLE_SID. The executables for different versions have the

same name.

On NT, all Oracle server installations must be in the same ORACLE_HOME (this

is no longer the case from 8.0.4). Versions are distinguished by having the

first two letters of the version at the end of their names, e.g. ORACLE73,

EXP80. This means that installation of one minor release, e.g. 7.3.2.3, will

overwrite another, e.g. 7.3.2.1, which may not have been the intended result.

18. What is meant by the terms "upgrade" and "migrate"?

The term upgrade is used to refer to moving from one minor release to a higher

minor release, e.g. 7.2.2.4 to 7.2.3. The term migrate is used to refer to

moving from one major release to a higher major release, e.g. 7.3.4 to 8.0.4.

19. What are the routes for transporting data between different platforms?

The tool for extracting data from an Oracle database is export. The file

it creates is written in a special, proprietary format, which can only be read

by the import utility. The latter may reside on another platform, so this 

route allows an Oracle database to be moved to a different platform. A less

sophisticated way of extracting data is to issue the appropriate SELECT query

in SQL*PLus, spooling the output to a file.

20. What is the difference between a server option and a server cartridge?

An option is an component of the Oracle Server which, when installed, becomes

part of the server kernel. The term cartridge denotes an option which provides

a user interface to the kernel, and which may, in a future release of the

server, become object-based. In some cases, for example ConText, what was an

option in Oracle7 is referred to as a cartridge in Oracle8. In other cases,

for example Parallel Query, what was an option has been included as a standard

part of the database.  

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