Oracle Process Architecture
PMON
- Cleans up cancelled processes - monitors other background processes - registers instance with SQL*Net Listener
Server processes can perform one or more of these
1- Parse and run SQL statements issued through the application. 2- Read necessary data blocks from datafiles on disk into the database buffers of the SGA, if the blocks are not already present in the SGA. 3- Return results in such a way that the application can process the information.
server and background processes
2 types of processes that run the Oracle database server code
Application or Oracle tool
A database user runs a database ________________, which issues SQL statements to an Oracle database
dedicated server process; shared server process
A server process can be either what type of process
Archiver Processes
ARCn
application or oracle tool; oracle database server code
All connected Oracle users must run two modules of code to access an Oracle database instance. These code modules are run by processes
30
An Oracle instance can have up to _____ ARCn processes (ARC0 to ARC9).
diminishes
As buffers are dirtied by user processes, the number of free buffer __________
Checkpoint Process
CKPT
checkpoint abbreviation
CKPT
Database Writer Process
DBWn
Oracle instance
Each process in an _________ performs a specific job
Oracle database server code
Each user has some______________ executing on his or her behalf, which interprets and processes the application's SQL statements
Manageability Monitor
Examples of? -Issuing alerts whenever a given metrics violates its threshold value. -Taking snapshots by spawning additional process (slaves). -Capturing statistics value for SQL objects which have been recently modified.
Every three seconds
How often does the LGWR write the redo log buffer to a redo log file on disk?
select count(*) from V$PROCESS;
How to check the currently active processes?
show parameter processes;
How to see the current number of processes which is set in the database?
recovers them when the tablespace or file is brought back online
If any terminated transactions were skipped during instance recovery because of file-read or offline errors, SMON _________. SMON checks regularly to see whether it is needed.
not able to find free buffers
If the number of free buffers drops too low, user processes that must read blocks from disk into the cache are ______________
Log Writer Process
LGWR
Memory Manager
MMAN
Manageability Monitor
MMON
background processes
Oracle uses _____________ to maximize performance and accommodate many users. An Oracle instance can have many of these; not all are always present.
CKPT background process
Oracle uses _________________ to automatically update each of the control files as needed, keeping the contents of all copies of the control synchronized
Process Monitor Process
PMON
Recovery if a user process fails; Cleaning up the database buffer cache; Registering the instance information with the listener
PMON is responsible for:
Queue Monitor Processes
QMNn
Queue Monitor Processes
QMPn
System Monitor Process
SMON
Increase the number of processes
Solution of error: ORA-00020: maximum number of processes (600) exceeded.
the current number of ARCn processes is insufficient to handle the workload
The LGWR process starts a new ARCn process whenever _____________
LGWR starts a new ARCn process
The alert log keeps a record of when ____________.
user processes; oracle processes
The processes in an Oracle system can be categorized into two major groups
Processes
This parameter specifies the maximum number of operating system user processes that can simultaneously connect to Oracle
buffer
When a _____ in the database buffer cache is modified, it is marked dirty
user process
When a user runs an application or an Oracle tool, Oracle creates a ______________ to run the user's application.
10
You can configure up to _____ queue monitor processes.
Server processes
_________ handle the requests of user processes connected to the instance
Connection; session
__________ and __________ are closely related to user process but are very different in meaning.
LOG_ARCHIVE_MAX_PROCESSES
_____________ parameter specifies the maximum number of ARCn processes that can be created.
User processes
_____________ run the application or Oracle tool code
Oracle processes
______________ run the Oracle database server code. They include server processes and background processes
cold buffer
a buffer that has not been recently used according to the Least Recently Used (LRU) algorithm
queue monitor process
an optional background process for Oracle Streams Advanced Queuing, which monitors the message queues. These processes are different from other Oracle background processes, if that process fails does not cause the instance failure.
LGWR
background process writes to the current redo log group whenever one of the following database events occurs: - Every three seconds. - A user commits a transaction. - The Redo Log Buffer is one-third full. - Before the DBWn process whenever a database checkpoint occurs.
alter system set processes=700 scope=spfile;
command to Increase the number of processes from 600 to 700
connection
communication pathway between a user process and an Oracle instance
ARCn
copies redo log files to a designated storage device after a log switch has occurred
CKPT process
does not write blocks to disk; DBWn always performs that work
checkpoint information
information that includes the checkpoint position, System Change Number (SCN), and location in online redo log to begin recovery
DB_WRITER_PROCESSES
initialization parameter that specifies the number of DBWn processes
background processes
manage memory structures: -Perform I/O to write data to a file on a disk. -Perform general maintenance tasks.
DBWn
manages the buffer cache so that user processes can always find free buffers
MMAN
manages the dynamic resizing of SGA memory areas as the workload increases or decreases
36
maximum number of DBWn processes
process
mechanism in an operating system that can run a series of steps
process
normally has its own private memory area in which it runs
LGWR
normally writes fast enough to ensure that space is always available in the buffer for new entries.
database buffer cache
part of the Oracle SGA that provides the following tasks: -Storage for data blocks that have been retrieved from data files. -Provides optimization boost for DML operations (UPDATES). -Data managed via the LRU algorithm.
SMON
performs recovery, if necessary, at instance startup
Manageability Monitor (MMON)
performs various manageability-related background tasks
Server processes
process created on behalf of each user's application
shared server process
process that can service multiple user processes
dedicated server process
process that services only one user process
ARCn
processes are present only when the database is in ARCHIVELOG mode, and automatic archiving is enabled
Redo log files
record all changes made to the database
SMON
responsible for cleaning up temporary segments that are no longer in use and for coalescing contiguous free extents within dictionary managed tablespaces
Log Writer Process (LGWR)
responsible for redo log buffer management
checkpoint process
responsible for updating file headers in the database datafiles and control files
session
specific connection of a user to an Oracle instance through a user process
server and background processes
two types of processes that run the Oracle database server code
CKPT process
updates the control file and data file headers with checkpoint information and signals DBW to write blocks to disk
MMAN
used for internal database tasks
V$BGPROCESS
view contains information about the background processes
LGWR
writes a commit record, when a user process commits a transaction
LGWR
writes all redo entries that have been copied into the buffer since the last time it wrote The redo log buffer is a circular buffer. When LGWR writes redo entries from the redo log buffer to a redo log file, server processes can then copy new entries over the entries in the redo log buffer that have been written to disk.
DBWn process
writes cold, dirty buffers to disk so that user processes are able to find clean buffers that can be used to read new blocks into the cache, so this improves the performance
LGWR
writes one contiguous portion of the buffer to disk.
database writer process (DBWn)
writes the contents of buffers to datafiles
LGWR
writes the redo log buffer to a redo log file on disk
checkpoint
writing by the DBW (database writer) process of all modified buffers in the SGA buffer cache to the database data files
