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The user who is making the change has not yet saved the transaction. Until that transaction is saved (referred to as committed in the world of Oracle Database 10g) or abandoned (referred to as rolled back in the same world), Oracle maintains a copy of the changed row in its undo tablespace.
Oracle Database 10g sometimes calls the system parameter file its spfile. This is where its startup parameters are defined and values in this file determine the environment within which the database operates. As one starts an Oracle instance, the spfile is read and various memory structures are allocated based on its contents.
Essentially, background processes facilitate access to the Oracle Database 10g and support the instance while it is running. These are the main background processes, many of their names not having changed over the past few releases prior to Oracle Database 10g.
Database writer (dbwr) processes are responsible for writing the contents of database buffers to disk. As sessions interact with the Oracle Database 10g, all the information they use passes through Oracle's database buffers, a segment of memory allocated for this activity.
The log writer (lgwr) process manages the writing of information to the online redo logs. A log buffer area is set aside in memory where information destined for the online redo logs is staged. The transfer of this information from memory to disk is handled by the lgwr process.
The checkpoint process (ckpt) is responsible for updating information in Oracle Database 10g's files during a checkpoint activity. A checkpoint is the activity of writing information from memory to the appropriate locations in the Oracle Database 10g. Think of a checkpoint as a stake in the ground allowing the restoration of a system to a specific point in time. The checkpoint process may trigger lgwr and dbwr to do their specialized tasks.
The system monitor (smon) process is the gatekeeper of consistency as the Oracle Database 10g runs. Consistency defines the interrelatedness of the database components with one another. A consistent instance must be established every time the Oracle Database 10g starts and it is smon's job to continually enforce and reestablish this consistency. Plainly put—an inconsistent database is trouble!
The process monitor (pmon) is responsible for cleaning up any resources that may have been tied up by aborted sessions interacting with the database. The famous CTRL-ALT-DEL that people tend to use to reboot a personal computer can leave resources tied up in the Oracle Database 10g. It is pmon's job to free up these resources.
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