Oracle commonly uesd tables/views and processes（一）

一、
Oracle commonly used tables
1、
DBA_USERS #DataBase users information

common column
username
user_id
account_status
lock_date
expiry_date
default_tablespace
temporary_tablespace
2、
DBA_SEGMENTS #describe the storage allocated for all segments in the database.

common column
owner
segment_name
segment_type
partition_name
tablespace_name
bytes
二、
Oracle commonly used processes
1、instance background processes

PMON :periodically check the status of the server process and restore abnormal processes 。
LGWR: to write the log  buffer contents to the redo log file,oracle writes the user chenges to the redo log file and then writes the data files.
CKPT:A checkpoint is an event that triggers DBWR to require dirty data to be written to a data file when a checkpoint occurs .LGWR writes to the log .
SMON:mandatory to perform  a recovery when the database is started . reclaim space to merge free and adjacent extents in the tablespace .clean up temporary tablespace/temporary segmentes.
ARCH:only started in archive mode .when the online redo logs  is full ,copy the log the spectfied location.
DBWR:writes the database buffer cache to the data files.