In rsa3 u have many option regarding the update mode (full, init, delta etc).
for LO - extractors , full or init will pull data from the setup tables.
for extracting delta - u have to give Update mode as D and u have to give the BW system so that it will pull delta records for that system.U can also check in RSA7 for the queued data.
if u want to check the last delta loaded in BW u can use update mode R and BW sys name so tat it will show the records in Repeat delta table.same thing u can check in RSA7 also.
In IP whenever you trigger the load from BI , through the RFC connection the background user goes to the extractor and this triggers a BGD job in source and pulls the data this is maintained in PSA Table.
Please refer to following link: