This content has been marked as final. Show 18 replies
926840 wrote:Flash Back Table,Flash Back Version Query , Flash Back Transaction Query are alls Flash Back Technology which uses Undo tablespaces and honored by Undo_Retention period ,from these technolgies you can restore deleted rows from tables.
Done..when i use the dba_recyclebin object it show the recycle object in recycle bin.
My another question is how old we go back for e.g if i delete some rows and drop the table in database.
While Flash Back Drop managed by Recycle Bin as i said earlier , it is the logical structure of dropped objects and physically contain within that objects own tablespace , it will be ever within that tabelspace to honor Recyclebin until and unless the said tablespace is run out of space , if space pressure towards this tablespace arise then first that objects within RecycleBin will be wiped out using FIFO method to deallocate extents to make room within that tablespace before it goes to autoextend.
FlashBack Log for dragging back yours whole database to past desried time , it is worked with db_flashback_rentention_target which tells how far back in time you can kick off yours database , with this you have to also maintain cyclic flashback logs till that past time and as well archivelogs.
then why we need undo_retention in flashback technology.Because entire Flashback technology is based on Undo data only, except Flashback database, which requires Flashback log and whose related parameter db_flashback_retention_target; thats why if someone asks something like
is confusing (specially, when you are going to compare them), because both are different ones. First one is related to undo data, while second is for flashback logs.
DB_FLASHBACK_RETENTION_TARGET is only relevant for flashback logs that are only written if you put your DB in flashback mode with alter database flashback on
For a flashback table, flashback logs are not needed, only for flashback database.
Edited by: Girish Sharma on Oct 11, 2012 7:15 PM
926840 wrote:As the name reveals that flashback "in literature and dramatic media, an interjected scene that takes the narrative back in time from the current point " , to flashback in database what should you have to go back.It makes sound for me some recorder to back the past.This recorder could be Undo (which honored by Undo_Retention , to make yourself own disposal to accomodate how far you wana back) , it is how designed by Oracle , i could not comments over it.To flashback whole database does not make sense to honored by Undo , yes it does by flashback logs and archivelogs which honored by db_flashback_retention_target.
Thanks alot sir,but clarify one more thing then why we need undo_retention in flashback technology.
Does it make sense?