Uncommited data in datafiles ?

[Sonia]

hi,
When an instance is up and running is there any situation
where in uncommited data can be present in datafiles (Except when oracle is doing istance recover)

Regards
sonia

[SANJAY_G]

Yes, uncommited data can be on datafiles.

[Sonia]

hi sanjay,

can u explain me...in what situation..

[hrishy]

Hi sonia

In many many situations..whenever dbwr is signalled to write dirty block to the database it just does that..and that dirty blocks will contain uncomitted data..now there are many conditions under which the dbwr flushes dirty buffers to disk and under these conditions dbwr will not check wheather the blocks contain comitted data or not it just flushes..

regards
Hrishy

[quester]

Originally posted by hrishy
Hi sonia

In many many situations..whenever dbwr is signalled to write dirty block to the database it just does that..and that dirty blocks will contain uncomitted data..now there are many conditions under which the dbwr flushes dirty buffers to disk and under these conditions dbwr will not check wheather the blocks contain comitted data or not it just flushes..

regards
Hrishy

Hrishy is right. For instance, DBWR wakes up every three seconds and writes all the dirty buffers to the data files (in Oracle 8i).

During instance recovery, SMON Rollsback all the uncommitted transactions.

[adewri]

well you can try it your self...

1. Create a small tablespace with 1M datafile(or what ever is the smallest possible for you);
2. Alter the datafile of this tablespace to autoextend on;
3. create a table in this tablespace and start inserting rows(say 80000 or more). Do not Commit;
4. Watch your datafile grow with uncommited data.

HTH

[abdulkhadeer]

yes uncommited data can be store in data files of the database . it is like this . when the dirty data buffer . is full .and there no free buffer space in the database buffer cache .and the checkpoint . indicate the dbwn to write the dirty to write in the datafile.