Two question.Help

[eastking]

hello ,every one here.

1.
I was told that an entry of rollback segment is relatived to a SCN which is owned by a transaction.
I was also told that SCN is given soon AFTER a commit executed.

My Problem is : Before a transaction commited, does a SCN relative to this
transaction exist? If not ,what is the entry in rollback segment relatived to it.

2.
The question is as following
All the space in datafile except for the header block can be accounted for in which two data dictionary
views?

the correct answer is DBA_EXTENTS and DBA_FREE_SPACE

But I do not know how can I use this two views to get the information which I want.

Thank you in advance

[denevge]

(2.)

select tablespace_name,sum(user_blocks)
from dba_data_files
group by tablespace_name
--> gives you a list how many blocks you can use per tablespace (total )

select tablespace_name,sum(blocks)
from dba_segments
group by tablespace_name
--> gives you a list per tablespace how many blocks are already in use ( used )

select tablespace_name,sum(blocks)
from dba_free_space
group by tablespace_name
-> gives you a list per tablespace how many blocks are available. ( free )

for each tablespace (total) = ( used ) + ( free )

for every datafile in you tablespace you lose 1 block that's used as the datafile header. ( in dba_data_files blocks - user_blocks = 1 )

Hope this helps
Gert

[nabaig]

To awnser your first query:

1. SCN is assigned after a transaction is comitted.
2. To achieve read consistency, Oracle will check the latest SCN and display data only upto the stage of that commit.
Because, another user might have changed data after that SCN which has still not been comitted and the data blocks might have uncomitted data. But the rollback will have the original of that data after the comitted SCN.

Hope this clarifies.

Nizar

[eastking]

thank you all