Together, the SGA and the background processes compose an
Oracle instance.
SMON
SMON is the System Monitor process. In the case of a system crash or instance failure, due to a
power outage or CPU failure, the SMON process performs crash recovery by applying the entries
in the online redo log files to the datafiles. In addition, temporary segments in all tablespaces are
purged during system restart.
One of SMON??™s routine tasks is to coalesce the free space in tablespaces on a regular basis if
the tablespace is dictionary managed.
36 Oracle Database 11g DBA Handbook
PMON
If a user connection is dropped, or a user process otherwise fails, PMON, also known as the
Process Monitor, does the cleanup work. It cleans up the database buffer cache along with any
other resources that the user connection was using. For example, a user session may be updating
some rows in a table, placing a lock on one or more of the rows. A thunderstorm knocks out the
power at the user??™s desk, and the SQL*Plus session disappears when the workstation is powered
off. Within moments, PMON will detect that the connection no longer exists and perform the
following tasks:
Roll back the transaction that was in progress when the power went out.
Mark the transaction??™s blocks as available in the buffer cache.
?–
?–
FIGURE 1-6 Oracle background processes
Chapter 1: Getting Started with the Oracle Architecture 37
Remove the locks on the affected rows in the table.
Pages:
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117