1. Database Administrator's Reference
  2. Oracle Database Architecture on Windows
  3. Overview of Oracle Database on Windows Architecture
  4. Thread-Based Architecture
  5. About Thread-Based Architecture

About Thread-Based Architecture

Oracle Database instance or an Oracle Automatic Storage Management instance architecture is thread-based.

Threads allow concurrent operations within an operating system process so that a process can run different parts of its program simultaneously on different processors. A thread-based architecture provides the following advantages:

  • Faster context switching

  • Shared memory segments

  • Faster spawning of new connections, because threads are created more quickly than processes

  • Decreased memory usage, because threads share more data structures than processes

Internally, the code to implement the thread model is compact and separate from the main body of Oracle Database code. Exception handlers are used to deallocate resources. They add robustness, with no downtime because of resource leaks or program that does not function as expected.

Oracle Database is not a typical Windows process. On Windows, an Oracle Database instance or an Oracle Automatic Storage Management instance (threads and memory structures) is a Windows service: a background process registered with the operating system. The service is started by Windows and requires no user interaction to start. This enables the database to open automatically at computer startup.

When running multiple Oracle Database or Oracle Automatic Storage Management instances on Windows, each instance runs its own Windows service with multiple component threads. The background processes read and write from various data files, depending on your configuration. Oracle Database architecture on Windows is illustrated in Figure 1-1. Examples of Oracle Database required threads on Windows are listed in Table 1-1 .

Figure 1-1 Oracle Database Architecture on Windows

Description of Figure 1-1 follows
Description of "Figure 1-1 Oracle Database Architecture on Windows"

Table 1-1 Oracle Database Threads

Oracle Database Thread Description Required/Optional

DBWO

database writer

Required

LGWR

log writer

Required

MMAN

memory manager process

Required

PMON

process monitor

Required

PSPO

process spawner process

Required

SMON

system monitor

Required

CKPT

checkpoint process (thread on Windows) that runs by default on Windows

Required

ARCO

archive process (or thread on Windows)

Required

RECO

distributed recovery background process

Required

Note:

You can view running background processes by executing the following query: 

SQL> select * from v$bgprocess where paddr <> '00';

Oracle Database instance or an Oracle Automatic Storage Management instance runs as a Windows Service. On Microsoft Windows, the entire instance runs as a single operating system process. Oracle Database instance contains two types of Oracle processes: background and foreground Oracle processes. Each of these Oracle processes is spawned as an operating system thread within in the Oracle Database instance.

Oracle Database for Microsoft Windows is supplied as a set of executables and dynamic link libraries (DLLs). Executable images can be modified using ORASTACK to change the size of the stack used by the threads of the Oracle Database process. Oracle recommends that you use this tool only under the guidance of Oracle Support Services.

Parent topic: Thread-Based Architecture