Undo Tablespace

[oramad]

Hello,

What does this dynamic extent transfer mean?

As of Oracle8i a transaction can span multiple extents in a rollback segment but cannot span multiple segments right?

Did this behaviour change in oracle9i?


Thanks in advance.

[stmontgo]

yes, i believe that in 9i a transaction can employ more than one rbs

[Dilippatel]

In 9i Transaction can not span over multilple Rollback segments.

[julian]

Originally posted by Dilippatel
In 9i Transaction can not span over multilple Rollback segments.

Not true.

When the first DML operation in a transaction is executed, an undo segment is chosen. The AUM transaction-bind algorithm first attempts to bind one transaction per undo segment. If such a segment cannot be found, the system will attempt to online another undo segment in the current undo tablespace. If none is available, a new undo segment is created and brought online. If none of the above steps succeed, the 8i approach is used, i.e., find the least used undo segment.

The AUM mode supports dynamic transfer of undo space between undo segments. If an executing transaction needs more undo space, space is reused either from the current undo segment or through an extension. If none of these steps results in enough free space for the transaction, free undo space is STOLEN from other undo segments.

Thus you will see ORA-30036 only of the undo tablespace is totally out of space.

[oramad]

Hello,

What does this dynamic extent transfer mean?

Thanks in advance.

[julian]

Originally posted by oramad
Hello,

What does this dynamic extent transfer mean?

Thanks in advance.

Read the text above and you will find out!

[jmodic]

Originally posted by julian
Not true.

When the first DML operation in a transaction is executed, an undo segment is chosen. The AUM transaction-bind algorithm first attempts to bind one transaction per undo segment. If such a segment cannot be found, the system will attempt to online another undo segment in the current undo tablespace. If none is available, a new undo segment is created and brought online. If none of the above steps succeed, the 8i approach is used, i.e., find the least used undo segment.

The AUM mode supports dynamic transfer of undo space between undo segments. If an executing transaction needs more undo space, space is reused either from the current undo segment or through an extension. If none of these steps results in enough free space for the transaction, free undo space is STOLEN from other undo segments.

Thus you will see ORA-30036 only of the undo tablespace is totally out of space.

But Dilippatel's statement still holds ("In 9i Transaction can not span over multilple Rollback segments.")! This hasn't change, in any release so far the transaction is bound to one rollback segment and one rollback segment only. What has change in 9i is how undo segment can be dinamicaly extended by using unused space from some other undo segment. However the basic rule "Transaction can not span over multiple undo segments" does still apply.