Oracle Query check How often and when does "Snapshot too old" (ORA-01555) occur

** Myself
##How often and when does "Snapshot too old" (ORA-01555) occur?
set linesize 140
select to_char(begin_time,'YYYY-MM-DD HH24:MI:SS') "Begin",
to_char(end_time,'YYYY-MM-DD HH24:MI:SS') "End ",
undoblks "UndoBlocks",undoblks*8/1024 "UndoBlocks(MB)",
SSOLDERRCNT "ORA-1555",MAXQUERYLEN "Query Time(sec)",MAXQUERYLEN/60/60 "Query Time(hr)"
from v$undostat
where SSOLDERRCNT > 0;

##Depending on the result: Increase the undo retention