No physical reads, plenty of consistant gets

Question

Hi All,
Oracle v11.2 on Linux.
Please have a look at the query I ran and the output. The SQL_ID is of a SELECT command.
What does this situation represents, where there are zero physical reads and plenty of consistant gets ?
For consistant gets, we do read undo information (correct ??), if that undo is read from disk, will that be a "physical read"? i.e. if we read disks for consistant gets, will that be counted under physical reads or not ?
How can I describe the exact data retrival of the command here? Is it the case of "everything it needs is found in the buffer cache" ?
select a.sid, a.value , B.NAME ,  s.sql_id
from v$sesstat a, v$statname b, v$session s
where A.STATISTIC# = B.STATISTIC#
and b.name in ( 'redo size','physical read bytes','physical reads cache','consistent gets' )
and a.sid = s.sid
and a.sid=1018
order by a.sid;
       SID      VALUE NAME                                                             SQL_ID
      1018    7281396 consistent gets                                                  434u36htuz0s9
      1018          0 physical reads cache                                             434u36htuz0s9
      1018          0 physical read bytes                                              434u36htuz0s9
      1018       4448 redo size                                                        434u36htuz0s9
4 rows selected.Thanks in advance.

Answer 1

>
There are no physical reads, so weather its doing consistant-gets or not, can I say, all data required for the SELECT was in buffer cache ?
>
The data for those system views is cached in memory so Oracle does not read the disk (except at startup) to gather the information.
Some static information, like dictionary objects, is stored stored on disk in the system tablespace but this data is read when the database is mounted and stored in memory structures.
Other dynamic information, like session info, is only stored in memory structures (similar to C arrays) and Oracle can query these as if they were tables.
So no, the data was not in the buffer cache. It was already in system memory.