Remove the process ID of the disconnected process from the list of active processes.
PMON will also interact with the listeners by providing information about the status of the
instance for incoming connection requests.
DBWn
The database writer process, known as DBWR in older versions of Oracle, writes new or changed
data blocks (known as dirty blocks) in the buffer cache to the datafiles. Using an LRU algorithm,
DBWn writes the oldest, least active blocks first. As a result, the most commonly requested
blocks, even if they are dirty blocks, are in memory.
Up to 20 DBWn processes can be started, DBW0 through DBW9 and DBWa through DBWj.
The number of DBWn processes is controlled by the DB_WRITER_PROCESSES parameter.
LGWR
LGWR, or Log Writer, is in charge of redo log buffer management. LGWR is one of the most
active processes in an instance with heavy DML activity. A transaction is not considered complete
until LGWR successfully writes the redo information, including the commit record, to the redo log
files. In addition, the dirty buffers in the buffer cache cannot be written to the datafiles by DBWn
until LGWR has written the redo information.
If the redo log files are grouped, and one of the multiplexed redo log files in a group is
damaged, LGWR writes to the remaining members of the group and records an error in the alert
log file. If all members of a group are unusable, the LGWR process fails and the entire instance
hangs until the problem can be corrected.
Pages:
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118