Difference between the Checkpoint and SCN

Checkpoint
———-
Checkpoint in database is used to reduce the amount of the time for recovery. It is a background process in oracle(CKPT), which cause DBWR to write all the data blocks that have been modified since the last checkpoint to the datafile.
Checkpoint is responsible for
->Signaling DBWn
->Updating datafile headers with checkpoint info. (i.e. SCN)
->Updating Control file with checkpoint info. (i.e. scn)

SCN
—–
SCN is the ever increasing number to determine the age of database.
it’s System Change Number / System Commit Number…
It’s used to determine the consistency of database..
It’s stored at various places like control file, data files, redo log files.
If it doesn’t match, that means inconsistency..

So in short,
Checkpoint is the concept/background process while SCN is like serial number in our table..

ORDER OF BACKGROUND PROCESSES DURING DB STARTUP

ORDER OF BACKGROUND PROCESSES DURING DB STARTUP

PMON
DBWR
LGWR
CKPT
SMON
RECO
ARCH

PDLCSRA- easy to remember

What is SCN.

System Change Number (SCN) This is a sequential counter identifying precisely a moment in the database.This is the most accurate way to identify a moment in time.

You can query
SELECT CURRENT_SCN FROM V$DATABASE;
or
SELECT DBMS_FLASHBACK.GET_SYSTEM_CHANGE_NUMBER FROM DUAL to get the current change number.

SYSAUX tablespace OFFLINE

Can you take the sysaux tablespace offline?
The sysaux tablespace is new with Oracle 10g. It is used to store database components that were stored in the system tablespace in prior releases of the database.
Also, the tablespaces that were needed for RMAN’s recovery catalog, for Ultra Search, for Data Mining, for XDP and for OLAP are going to sysaux with 10g.
Additionally, it is the place where automatic workload repository stores its information.

You can make the SYSAUX tablespace offline. This is if you wish to make the tablespace unavailable. If you make the sysaux tablespace offline then you will not be able to use the features that uses this tablespace.