Redo undo for temporary Oracle tables

1. A large number of redo records are generated for the insert operation of the Permanent Table, but almost no redo is generated for the temporary table. This makes sense. insert on a temporary table will only generate a small amount of Undo data, and only create logs for the temporary table.

 

2. The redo generated by the update of the Permanent Table is about twice the redo generated by the update of the temporary table. This is also reasonable. About half of update must be saved (that is, the previous image ). For temporary tables, you do not need to save the "Post image" (redo ).

 

3. Delete requires almost the same redo space. This makes sense, because the Undo of Delete is large, and the redo of modified blocks is small. Therefore, the delete operation on the temporary table is almost the same as the delete operation on the permanent table.

 

For the last conclusion, we need to point out some exceptions. For example, if we use a 2000-byte data update column that is completely null, very few undo data will be generated. This update is like insert. On the other hand, if I update a column with 2000 bytes of data to all null, for redo generation, this is like Delete. On average, we can think that the temporary table update is 50% of the latter compared with the Undo/Redo generated by the Permanent Table update.