The Oracle Server Architecture document outlines the core components that make up an Oracle database instance, including background processes, memory structures like the system global area (SGA) and program global area (PGA), online redo logs, control files, and more. It shows how client connections are handled by the database and how resources are shared between users. Key processes keep the database functioning and recoverable, while memory areas cache data and SQL for fast access.

1. Oracle Server Architecture
Node x
Database DIAG FMON EMN0 (Background Processes) RSM0 NSV0 Instance x Client
Controlfiles
Thread x SMON RECO PMON CJQ0 Jnnn Snnn Dnnn DB Application
DMON Dedicated Sever - Forms
LGWn CKPT DBWn FAL Server Agent
(+ Config File) ORA<xxx> - Reports
Group 1 Group 2 Group 3 ("User" Process) - SQL*Plus
ARCn LMON LMD0 LMSn LCK0 GSD CM - Embedded SQL (C, Java, Cobol)
(mirrored)
Archive Logs (All Threads)
(Instance Recovery)
DIAG FMON EMN0 (Background Processes) Instance 1 Client/Server
Parameter File SMON
RECO LMON LMD0 LMSn LCK0 CJQ0 Jnnn RSM0 NSV0 PMON
ARCn Net Services
Thread 1 Online Redo Logs (mirrored) SGA PGA
(static) Session Memory (Instance Registration)
Log Large Pool
Password File Buffer Fixed SGA - Parallel exec. message
Group 1 Group 2 Group 3 LGWR buffers Private SQL
- RMAN backup/restore DMON
(asynch)
Tablespaces
(synch)
Persistent Area (+ Config File)
Alert.log - Shared Server UGA
Java Pool
(System, Undo_Inst_1, Undo_Inst_x, (User Session Memory)
- Bind Data
Listener
Temp, Tables, Indexes)
Buffer Cache Shared Pool (dynamic*) Runtime Area
Agent
- Block buffers within - Work Areas (Workload Update)
Library Cache Dictionary
File 1 Header pools (default, keep, (Sort, Hash,
CKPT recycle)
- Shared SQL Cache
Bitmap Merge/
Trace Files Segment 1 Header - PL/SQL (Rowcache)
- Subcaches for each Create)
(Dump Destination) Extent 1 - DB Objects
block size (min. 1 Control - Users (tunable) N-Tier
Block Block Block granule) Structures - Privs
(dynamic*)
DBWn Block
Reserved Pool Dedicated Server
(LRU Ageing) (LRU Ageing)
External Tables Extent n ORA<xxx> Application Server
Response Queue Request Queue ("User" Process)
Segment n LNSV
GSD PGA
Cache Stack Space
File n FAL Server CM Snnn Dnnn
QMNn (Shared Server) (Dispatcher) Data Guard Broker
- Manager
Storage Subsystem (*granule unit size: 4MB if SGA < 128MB, 16MB otherwise) Node 1 - CLI
(Log Transport Services)
Server Management
Standby - Server Control
FAL Client
Controlfile RFS OSD Clusterware
Standby Redo Logs LSPn Enterprise Manager
ARC0
(Log Apply Services)
RAC Guard
Parameter File Failsafe
Archive Logs
MRP0
(or foreground process)
Managed Recovery
Utilities
(Plus Standard Directory Services
- Export / Import
Background Processes) Heterogeneous Services
- SQL*Loader
DB Files DMON Advanced Replication
- Recovery Manager
(+ Config File) Advanced Queuing
Standby Database Instance
Storage Subsystem Standby Node
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