| Checkpoint types [message #291447] |
Fri, 04 January 2008 04:33  |
gajini
Messages: 262
Registered: January 2006
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Senior Member |
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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...
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| Re: Checkpoint types [message #291459 is a reply to message #291447] |
Fri, 04 January 2008 05:00  |
varu123
Messages: 754
Registered: October 2007
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Senior Member |
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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
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| Re: Checkpoint types [message #291471 is a reply to message #291447] |
Fri, 04 January 2008 05:32 |
varu123
Messages: 754
Registered: October 2007
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Senior Member |
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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.
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| 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.
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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?
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| Re: Checkpoint types [message #292163 is a reply to message #291447] |
Tue, 08 January 2008 01:54 |
gajini
Messages: 262
Registered: January 2006
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Senior Member |
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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...
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| Re: Checkpoint types [message #292168 is a reply to message #291447] |
Tue, 08 January 2008 02:13 |
varu123
Messages: 754
Registered: October 2007
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Senior Member |
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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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