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Checkpoint types [message #291447] Fri, 04 January 2008 04:33 Go to next message
gajini
Messages: 259
Registered: January 2006
Senior Member
Hi,

what is the difference between
thread checkpoint,
database checkpoint and
datafile checkpoint?

I read those things in Oracle doc,but i couldn't understand,
Can anyone explain these things with a simple example...

Thanks...
Re: Checkpoint types [message #291450 is a reply to message #291447] Fri, 04 January 2008 04:43 Go to previous messageGo to next message
Michel Cadot
Messages: 64132
Registered: March 2007
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Quote:

I read those things in Oracle doc

Point where in the documentation.

http://download.oracle.com/docs/cd/B19306_01/backup.102/b14192/glossary.htm#sthref852
http://download.oracle.com/docs/cd/B19306_01/server.102/b14220/glossary.htm#i431992
(-> Edit/Find/checkpoint)

Regards
Michel

[Updated on: Fri, 04 January 2008 04:45]

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Re: Checkpoint types [message #291459 is a reply to message #291447] Fri, 04 January 2008 05:00 Go to previous messageGo to next message
varu123
Messages: 754
Registered: October 2007
Senior Member
database checkpoint and datafile checkpoint are one and the same thing
Checkpoint can be classified into two types,full and incremental
What is thread checkpoint?
MUst be the same thing
Re: Checkpoint types [message #291462 is a reply to message #291459] Fri, 04 January 2008 05:19 Go to previous messageGo to next message
Michel Cadot
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Quote:

database checkpoint and datafile checkpoint are one and the same thing

Wrong. Datafile checkpoint can be different than database one, for instance if datafile is put in read only mode.

Quote:

What is thread checkpoint?
MUst be the same thing

See the first link I posted.

Regards
Michel
Re: Checkpoint types [message #291471 is a reply to message #291447] Fri, 04 January 2008 05:32 Go to previous messageGo to next message
varu123
Messages: 754
Registered: October 2007
Senior Member
This is from the glossary:
Quote:

database checkpoint

The thread checkpoint that has the lowest SCN. All changes in all enabled threads prior to the database checkpoint are guaranteed to have been written to disk.


Quote:

checkpoint

A data structure that defines an SCN in the redo thread of a database. Checkpoints are recorded in the control file and each datafile header, and are a crucial element of recovery.



when a checkpoint occurs,all the data buffer cache flushes out to data files and all the datafiles and controlfiles are marked with the same SCN which is just a number.
Checkpoint is an event that marks the datafile header with same SCN.
It ensures that all the data has been written to disk.

This is what a database checkpoint do.
Whats the difference?


Re: Checkpoint types [message #291472 is a reply to message #291471] Fri, 04 January 2008 05:36 Go to previous messageGo to next message
Michel Cadot
Messages: 64132
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Database checkpoint refers to ALL threads that is all instances in RAC.
Checkpoint (alone) refers to thread checkpoint.

Regards
Michel
Re: Checkpoint types [message #292163 is a reply to message #291447] Tue, 08 January 2008 01:54 Go to previous messageGo to next message
gajini
Messages: 259
Registered: January 2006
Senior Member
Hi,


In oracle 10g documentation,they've given that,
"DBWn periodically writes buffers to advance the checkpoint, which is the position in the redo thread (log) from which instance recovery begins. This log position is determined by the oldest dirty buffer in the buffer cache."

In this I didn't understand the this line,"This log position is determined by the oldest dirty buffer in the buffer cache.",can anyone explain how oldest dirty buffer determines log position?

Thanks...
Re: Checkpoint types [message #292168 is a reply to message #291447] Tue, 08 January 2008 02:13 Go to previous message
varu123
Messages: 754
Registered: October 2007
Senior Member
Oldest probably means that the oldest dirty buffer written to datafile with the current checkpoint.
For ex,,
d1---oldest dirty buffer[checkponted]
d2
d3
d4--latest dirty buffer

Am i right?
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