• Database writer (DBWRn)
The database writer writes modified blocks from the database buffer cache to the
files on a disk.
Oracle Database allows a maximum of 36 database writer processes.
• Log writer (LGWR)
The log writer process writes redo log entries to disk.
Redo log entries are generated in the redo log buffer of the System Global Area
(SGA) and the log writer process writes the redo log entries sequentially into an
online redo log file.
• Checkpoint (CKPT)
At specific times, all modified database buffers in the SGA are written to the data
files by a DBWR.
The checkpoint process signals DBWRn, updates the data files and control files of
the database, and records the time of this update.
• System monitor (SMON)
The system monitor performs instance recovery when a failed instance is
• Process monitor (PMON)
The process monitor performs a recovery when a user process fails.
It cleans up the cache and frees resources that the failed process was using.
Other Background Processes
• Archiver (ARCn)
Archiver processes copy the online redo log files to archival
storage when the log files are full or a log switch occurs.
• Manageability monitor (MMON)
This process performs various management-related
background tasks, for example:
Issuing alerts whenever a given metric violates its threshold value
Taking snapshots by spawning additional processes
Capturing statistical values for SQL objects that have been
• Job Queue Processes (CJQ0 and Jnnn)
Job queue processes run user jobs, often in batch mode. A job
is a user-defined task scheduled to run one or more times.
System Global Area(SGA)
• Database buffer cache
Before data stored in the database can be queried or modified, it
must be read from a disk and stored in the buffer cache.
All user processes connected to the database share access to the
For optimal performance, the buffer cache should be large enough
to avoid frequent disk I/O operations.
• Shared pool
SQL statements that can be reused
Information from the data dictionary such as user account data,
table and index descriptions, and privileges
Stored procedures, which are executable code that is stored in the
• Redo log buffer
This buffer improves performance by caching redo information
until it can be written to the physical online redo log files stored
Other SGA Component
• Result cache
The result cache buffers query results.
If a query is run for which the results are stored in the result
cache, then the database returns the query results from the
This SGA component speeds the execution of frequently run
• Large pool
This optional area is used to buffer large I/O requests for various
• Java pool
The Java pool is an area of memory that is used for all session-
specific Java code and data within the Java Virtual Machine
• Streams pool
The Streams pool is an area of memory that is used by the Oracle
Program Global Area(PGA)
• A Program Global Area (PGA) is a memory area used by a
single Oracle Database server process.
• When we connect to an Oracle database instance, we create
a session that uses a server process for communication
between the client and database instance.
• Each server process has its own PGA.
• The PGA is used to process SQL statements and to hold
logon and other session information.
• The amount of PGA memory used and the contents of the
PGA depend on whether the instance is running in
dedicated server or shared server mode.
• The total memory used by all individual PGAs is known as
the total instance PGA memory, or instance PGA.
• Setting the size of the instance PGA in Database Control
Files, not individual PGAs.
• Clustering OS
Windows Server Enterprise Edition, 啟用Cluster服務
• Oracle Grid Infrastructure
Oracle Automatic Storage Management(ASM)
• Server Hardware (for each node)
Physical memory (at least 1.5 gigabyte (GB) of RAM)
An amount of swap space equal to the amount of RAM
Temporary space (at least 1 GB) available in /tmp
All servers that are used in the cluster must have the same chip
architecture, for example, all 32-bit processors or all 64-bit
• Oracle Universal Installer verifies that your server and
operating system meet the listed requirements.
• SAN or NAS
• Fiber Channel or iSCSI and Logical Unit Number(LUN)
• RAID 5, 6 or 10
• At least 5.5 GB of available disk space for
The Grid home directory
The binary files for Oracle Clusterware, Oracle Automatic
Storage Management (Oracle ASM) and their associated log
• At least 4 GB of available disk space for the Oracle
Database home directory, or Oracle home directory.
• Oracle ASM
• Each node must have at least two network interface cards (NIC).
• One adapter is for the public network interface and the other adapter is
for the private network interface (the interconnect).
• For Public interface
The names must be the same for all nodes.
• For Private interface
The names must be the same for all nodes as well.
Support the user datagram protocol (UDP).
Using high-speed network adapters and a network switch(Gigabit Ethernet or
Every node in the cluster must be able to connect to every private network
interface in the cluster.
• The host name of each node must conform to the RFC 952 standard,
which permits alphanumeric characters.
• Host names using underscores ("_") are not allowed.
• GNS virtual IP address (GNS installations only)
GNS: Grid Naming Service
• Single Client Access Name (SCAN)
• Virtual IP address
• Public IP address
• Private IP address