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Background Processors

Background Processors

PMON : It is responsible for following actions
  1. releases the locks and resources held by abruptly terminated sessions
Note: whenever any user performs DML transactions on a table, oracle will apply lock. This is to maintain read consistency
  1. authenticates the user
  1. registers the listener information with the instance
  1. restarts dead dispatchers at the time of instance recovery in case of shared server architecture
DBWRn: It is responsible in writing dirty buffers from write list to datafiles and it will do this action in following situations
  1. after LGWR writes
  2. when write list reaches threshold value
  3. at every checkpoint
  4. when tablespace is taken offline or placed in read-only mode
  5. when database is shutdown cleanly
LGWR : It is responsible for writing redo entries from log buffer cache to redolog files and it will perform this in following situations
  1. before DBWRn writes
  2. whenever commit occurs
  3. when log buffer cache is 1/3rd full
  4. when 1 MB of redo is generated
  5. every 3 sec
CKPT : it will update the latest SCN to control files and datafile header by taking information from redolog files. This will happen at every log switch
ARCHn : It will generated offline redolog files in specified location. This will be done only if database is in archivelog mode
DATAFILES : actual files where user data will be stored
REDOLOG FILES : files contains redo entries which are helpful in database recovery. To avoid space constraints oracle will create two or more redolog files and LGWR will write into them in a cyclic order
REDOLOG FILE
CONTROL FILES : These files will store crucial database information like
  1. database name and creation timestamp
  2. latest SCN
  3. location and sizes of redolog files and datafiles
  4. parameters that define the size of controlfile
ARCHIVED REDOLOG FILES : These files will be created by ARCHn process if archivelog mode is enabled. The size of archives will be equal or less than redolog files
Read More:
PHASES OF SQL EXECUTION
OPERATING SYSTEM FUNCTIONALITY THEORY
Upgrading to Oracle Database 10G to 11G

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