Interpretation of the table

ColumnExplanation
Undo BlocksRepresents the total number of undo blocks consumed. You can use this column to obtain the consumption rate of undo blocks, and thereby estimate the size of the undo tablespace needed to handle the workload on your system.
# TXNIdentifies the total number of transactions executed within the period.
Max Qry Len (s)Identifies the length of the longest query (in number of seconds) executed in the instance during the period. You can use this statistic to estimate the proper setting of the UNDO_RETENTION parameter.
Max Tx ConcurcyIdentifies the highest number of transactions executed concurrently within the period.
Snapshot Too OldIdentifies the number of OER errors occurring within a period. You can use this statistic to decide whether or not the UNDO_RETENTION parameter is set properly given the size of the undo tablespace. Lowering the UNDO_RETENTION value can reduce the occurrence of this error.
Out of SpaceIdentifies the number of OER errors reported in the current instance. If there is a nonzero value in this column, the current undo tablespace needs more space (in the UNDO_RETENTION parameter).
uSThe number of attempts to obtain undo space by stealing unexpired extents from other transactions.
uRThe number of unexpired blocks removed from certain undo segments so they can be used by other transactions.
uUThe number of unexpired undo blocks reused by transactions.
eSThe number of attempts to steal expired undo blocks from other undo segments.
eRThe number of expired undo blocks stolen from other undo segments
eUThe number of expired undo blocks reused within the same undo segments