scn_to_timestamp(v_scn) returns the timestamp, with a resolution of three seconds, at which the System Commit Numberv_scn as generated.
The following query selects all timestamps of the past period and counts how often they occurred. It shows that the granularity of scn_to_timestamp is indeed three seconds:
with x(scn, ts) as (
select
dbms_flashback.get_system_change_number scn,
scn_to_timestamp(dbms_flashback.get_system_change_number) ts
from
dual
union all
select
x.scn -1,
scn_to_timestamp(x.scn-1)
from
x
where
scn_to_timestamp(x.scn-1) > sysdate - 1/24/60
)
select
count(*),
ts
from
x
group by
ts
order by
ts desc;