PL/SQL transaction boundries and CR blocks

Question

I have this scenario:
DBMS_SQL is used to build a select statement, within the statement only select is done is against the primary table. The results of the select are then used to do a summary and the summary is inserted into a second table. After X number of inserts there is a commit.
If all of this is within a BEGIN/END block in PL/SQL and multiple threads are used to do various sections of the primary table (30) if there is block overlap in the selects will CR blocks be required? Remember, even though the SELECT is part of a larger transaction as defined by the BEGIN/END no actual IUD is done against the primary table.
MIke

Answer 1

I'm not sure If I understood your CR abbreviation correctly. but I think it depends on the isolation mode that is used. Usually a select should not read the changes from other transactions. However it would read all changes from the current transaction. If the transaction isolation level is set to serialize this is different.
Also your pseudo code example is a little problematic since it doesn't include when the cursor is closed and if there is a loop to select other rows.
Remember that commits inside an opened cursor are "forbidden". For such constructs oracle can't guarantee read consistency for the full life of the cursor.
example of bad code (pseudo)
BEGIN
Create a SQL statement to fetch a range of base table rows
OPEN the SQL cursor created 
fetch
loop until EOF
  Summarize the returns
  INSERT summary rows into a second table
  COMMIT;
  fetch
end loop;
END;
close cursor;Furthermore the undo-retention time might influence how long a long running query can still select the original data set.
http://download.oracle.com/docs/cd/B19306_01/appdev.102/b14251/adfns_sqlproc.htm#i1024718