How DB adapter works when polling strategy is "remove row selected"?

Question

How DB adapter works when polling strategy is "delete the rows that were read"?
I want to know how database adapter works when polling startegy is "remove row".This polling strategy helps for polling the changes to table and remove records after new records are inserted or changes are done to table.Here,i want to understand how DB adapter identifies which record to be deleted.
For example: there is a table with 100 recorrds.How DB adapter works when polling strategy is "delete the rows that were read"?
I want to know how database adapter works when polling startegy is "delete the rows that were read".This polling strategy helps for polling the changes to table and remove records after new records are inserted or changes are done to table.Here,i want to understand how DB adapter identifies which record to be deleted.
For example:
There is a table EMP with 100 recorrds.Now, i deploy a BPEl process with db adapter polling on table EMP for changes.So that ,if any change happen to records in table that records will be picked up.I use a polling startegy "delete the rows that were read" .
Now i insert 9 new records and update one existing records.These 10 records should be picked up and then deleted by Db adapter.In this 109 records how DB adapter identifies these 10 records when it polls.How it differentiatess old records with new records when there is no flag field or no sequence id used to identify the new or modified records.
Please let me know.
Why i want to know this?
Some times customer may not allow BPEL process to do any modifications to source table or source database.In this case the options provided by database adapter wizard are not useful.
If there is any mechanism to identify new or modified records without having a FLAG field or sequence table,then it is possible to have an option like only read the changes from table rather than deleting the records after reading.Which helps in meeting above requirement.
Please let me know if there is any way to do this.
thanks
Arureddy

Answer 1

Once the record has been read it is deleted. Therefore, you can update rows in this table as many times you like before it is read. Once it is read there will be nothing to update as it will be deleted.
If you don't want to use a sequence table, you can use a sequence file. You can only use this functionality if the key you are using increments sequentially. e.g. 1,2,3,4. If your key is random, e.g. 2,1,3,5,7,4 then your options are delete or use a processing flag.
The other option is to create a trigger that inserts a key into a polling table when insert or updates occur. You can then use the delete, which is the most desirable as it uses database locking.
cheers
James