Kamran Agayev A.
Managing Oracle Database Processes
Oracle database creates server processes to handle the
requests of user processes connected to an instance.
Your database is always enabled to allow dedicated server
processes, but you must specifically configure and enable shared
server by setting one or more initialization parameters
Shared server can be configured for session multiplexing,
which combines multiple sessions for transmission over a single
network connection in order to conserve the operating system’s
- DBW – The database writer writes modified blocks from the
database buffer cache to the datafiles. Oracle database allows a
maximum of 20 database writer processes. The DB_WRITER_PROCESSES
initialization parameter specifies the number of DBW processes.
- LGWR – the log writer process writes redo log entries to
disk. Redo log entries are generated in the redo log buffer of the
SGA. LGWR writes the redo log entries sequentially into a redo log
file. If the database has a multiplexed redo log, then LGWR writes
the redo log entries to a group of redo log files.
- CKPT – At specific times, all modified database buffers
in the system global area are written to the datafiles by DBW. This
event is called a checkpoint. The checkpoint process is responsible
for signaling DBW at checkpoints and updating all the datafiles and
control files of the database to indicate the most recent
- SMON – the system monitor performs recovery when a failed
instance starts up again. SMON also cleans up temporary segments
that are no longer in use and recovers dead transactions skipped
during system failure and instance recovery because of file-read or
- PMON – the process monitor performs process recovery when
a user process fails. PMON is responsible for cleaning up the cache
and freeing resources that the process was using.
- RECO – the recoverer process is used to resolve
distributed transactions that are pending because of a network or
system failure in a distributed database. The following views help
you to monitor the Oracle instance
- V$PROCESS – Contains information
about the currently active processes
- V$LOCKED_OBJECT – Lists all locks
acquired by every transaction on the system
- V$SESSION – lists session
information for each current session
- V$SESS_IO – contains I/O statistics
for each user session
- V$SESSION_WAIT – lists the
resources or events for which active sessions are waiting
- V$SYSSTAT – Contains session
- V$SQLAREA – Contains statistics
about shared SQL area and contains one row for each SQL string
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