What is relationship (delete,insert,update) and undo?
during an insert - we have to generate undo equivalent to "delete+rowid"
during an update - we have to generate undo equivalent to "update this rowid to have these before image values" (undo = rowid + column before images)
during a delete - we have to generate undo equivalent to "insert at this rowid these values"
so, considering an unindexed table - IN GENERAL, a delete and update will generate the most and an insert the least. IN GENERAL this is true (but not always).
if you add indexes - everything can change. the insert might generate gobs of undo for the index maintenance - the update might not update any indexed columns and hence only generate undo for the table - and the delete might have to maintain all of the indexes generating tons of undo again.
so, it depends on the nature of the data, what you are inserting/updating/deleting..
same for redo. It depends on what is modified...
Undo(table of indexes) 产生量排序：delete>insert>update
来自 “ ITPUB博客 ” ，链接：http://blog.itpub.net/26442936/viewspace-774756/，如需转载，请注明出处，否则将追究法律责任。