Log Writer(LGWR):
Log writer writes the trasactional data from redolog buffer to redolog files under the following situations.
When transaction commits.
When redolog buffer one third full
Every Three Seconds
When there is more than 1MB of changes recorded in the redolog buffer
Shutting down the database.
Whenever checkpoint occurs.
DB Writer(DBWR):
DB Writer writes the Data from Database buffer to database files under following situations
Every Three Seconds
When DB shutdown
When check point occurs
The number of dirty buffer reaches threshold values
Placing tablespace in read only mode
Alter tablespace tablespace_name begin backup
Program Monitor Background Process (PMON):
A user may be disconnected either by cancelling its session or by communication link. In either act, the PMON will start and perform an action to clean the reminding memory allocation that was assigned to the user.
System Monitor(SMON):
If the Oracle instance fails, Any information in the SGA that has not been written into disks is lost.
For example, The failure of operation system causes as instance failure. After the loss of the instance,The back ground process SMON automatically performs instance recovery when the database is reopened . Instance recovery consists of the following steps:
1. Rolling forward to recover the data that that has not been recorded in the datafiles, but that has been recorded in the online redolog files.This data has not been written to disks because of the loss of the SGA during instance failure. During this process SMON reads te redolog files and write data
When you start your database, the SMON will make sure that all datafiles, controlfiles, and log files are synchronized before opening a database. If they are no, it will perform an instance recovery. It will check the last SCN that was performed against the datafiles. If it finds that there are transactions that were not applied against the datafile, then it will recover or synchronize the datafile from either the Online Redo Log files or the Archive Log files. The smaller Online Redo log files will bring a faster database recovery.
CheckPoint Background Process (CKPT):
The Checkpoint signals DB writers to write all dirty blocks into the disk. The Checkpoint will occurred either by a specific defined time, size of the Online Redo Log file used by DBA, or when an Online Redo log file will be switched from on log file to another. The following are the parameters that will be used by a DBA to adjust time or interval of how frequently its checkpoint should occur on its database.
LOG_CHECKPOINT_TIMEOUT = 3600 # every one hour
LOG_CHECKPOINT_INTERVAL=1000 # number of Operating System blocks
ARCHIVE Background Process (ARCH):
This background process archives the Online Redo Log file when you are manually or automatically switching an Online Redo Log file. An example of manually switching is:
ALTER SYSTEM SWITCH OGFILE or ALTER SYSTEM ARCHIVE LOG CURRENT.
Log writer writes the trasactional data from redolog buffer to redolog files under the following situations.
When transaction commits.
When redolog buffer one third full
Every Three Seconds
When there is more than 1MB of changes recorded in the redolog buffer
Shutting down the database.
Whenever checkpoint occurs.
DB Writer(DBWR):
DB Writer writes the Data from Database buffer to database files under following situations
Every Three Seconds
When DB shutdown
When check point occurs
The number of dirty buffer reaches threshold values
Placing tablespace in read only mode
Alter tablespace tablespace_name begin backup
Program Monitor Background Process (PMON):
A user may be disconnected either by cancelling its session or by communication link. In either act, the PMON will start and perform an action to clean the reminding memory allocation that was assigned to the user.
System Monitor(SMON):
If the Oracle instance fails, Any information in the SGA that has not been written into disks is lost.
For example, The failure of operation system causes as instance failure. After the loss of the instance,The back ground process SMON automatically performs instance recovery when the database is reopened . Instance recovery consists of the following steps:
1. Rolling forward to recover the data that that has not been recorded in the datafiles, but that has been recorded in the online redolog files.This data has not been written to disks because of the loss of the SGA during instance failure. During this process SMON reads te redolog files and write data
When you start your database, the SMON will make sure that all datafiles, controlfiles, and log files are synchronized before opening a database. If they are no, it will perform an instance recovery. It will check the last SCN that was performed against the datafiles. If it finds that there are transactions that were not applied against the datafile, then it will recover or synchronize the datafile from either the Online Redo Log files or the Archive Log files. The smaller Online Redo log files will bring a faster database recovery.
CheckPoint Background Process (CKPT):
The Checkpoint signals DB writers to write all dirty blocks into the disk. The Checkpoint will occurred either by a specific defined time, size of the Online Redo Log file used by DBA, or when an Online Redo log file will be switched from on log file to another. The following are the parameters that will be used by a DBA to adjust time or interval of how frequently its checkpoint should occur on its database.
LOG_CHECKPOINT_TIMEOUT = 3600 # every one hour
LOG_CHECKPOINT_INTERVAL=1000 # number of Operating System blocks
ARCHIVE Background Process (ARCH):
This background process archives the Online Redo Log file when you are manually or automatically switching an Online Redo Log file. An example of manually switching is:
ALTER SYSTEM SWITCH OGFILE or ALTER SYSTEM ARCHIVE LOG CURRENT.
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