View the Exhibit and examine the attributes of an undo tablespace. In an OLTP system, the user
SCOTT has started a query on a large table in the peak transactional hour that performs bulk
inserts. The query runs for more than 15 minutes and then SCOTT receives the following error:
ORA-01555: snapshot too old
What could be the reason for this error?
A.
The query is unable to get a read-consistent image.
B.
There is not enough space in Flash Recovery Area.
C.
There is not enough free space in the flashback archive.
D.
The query is unable to place data blocks in undo tablespace.
Explanation:
The ORA-01555 is caused by Oracle read consistency mechanism. If you have a long running
SQL that starts at 10:30 AM, Oracle ensures that all rows are as they appeared at 10:30 AM, even
if the query runs until noon! Oracles does this by reading the “before image” of changed rows from
the online undo segments. If you have lots of updates, long running SQL and too small UNDO, the
ORA-01555 error will appear.