alter system archive log all;
alter system archive log next;
alter system archive log sequence 104;
alter system archive log current;
alter system archive log current noswitch;
The following command can be used to stop arch.
alter system archive log stop
Similarly, arch is started with
alter system archive log start
However, changing the archiver this way doesn't last when the database is restarted. When the database is started, it consults log_archive_start in the initialization file to determine if arch is started.
This command is used to manually archive redo logs.
This command kills a session. The sid and serial parameters are found in the v$session view.
create or replace procedure kill_session(sid in number, serial in number) as
execute immediate 'alter system kill session ''' || sid || ',' || serial || ''' immediate';
Note: The alter system kill session statement will not make the session go away until it times out or it tries to issue another statement. However, pmon will rollback the work done by the session.
The server process waits then until the client tries to execute another statement to send it a ORA-03113 EOF on communication channel or "packet write failure". This is why killed sessions still show up in the v$session view.
However, if dead client detection (or is it dead connection detection?) is enabled, the session is removed as soon as the expiry time is reached.
To immediately release the locks (immediatly meaning: after the session's rollback), one should use kill -9 on unix or orakill on unix.
Performs a checkpoint
alter system checkpoint
This command can be used in order to dump one ore more blocks of a datafile. The following command dumps blocks 50 through 55 of file 5. Which file 5 is can be found out with v$datafile
alter system dump datafile 5 block min 50 block max 55;
Note: trace files are only readable by the Oracle account. If you want to change this, set the undocumented initialization parameter _trace_files_public to true. Doing so will, however, cause a big security risk.
alter system flush buffer_cache;
This command is not available prior to 10g. It flushes the buffer cache in the SGA.
9i had an undocumented command to flush the buffer cache:
alter session set events = 'immediate trace name flush_cache';
alter system flush buffer_pool;
This command flushed the shared pool.
Causes a redo log switch.
alter system switch logfile;
If the database is in archive log mode, but the ARCH process hasn't been startedm, the command might hang, because it waits for the archiving of the 'next' redo log.
Forces the registration of database information with the listener.
alter system register
Setting timed_statistics=true might be usefule when using tk prof.
Setting sql_trace=true is a prerequisite when using tk prof.
Alter system can be used to change initialization parameters on system level. However, some parameters, when changed with alter system don't affect sessions that are already opened at the time when the statement is executet; it only affects sessions started later. These parameters must be changed with alter system set
These parameters can be identified as they have a DEFERRED in the isses_modifiable column of v$parameter.
Resets a parameter.
alter system reset some_param scope=both sid='*';
Changes the parameter's value for the running instance only. As soon as the instance is stopped and started, this change will be lost.
Alters an initialization parameter in the spfile
Alters an initialization parameter in the spfile as well as in the running instance.
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