Statspack Io operations and buffer hit rate

-- Physical zookeeper operation
Select distinct to_char (snap_time, 'yyyy-mm-dd hh24: MI: ss') datetime,
(Newreads. Value-oldreads. Value) reads,
(Newwrites. Value-oldwrites. Value) writes
From perfstat. Stats $ sysstat oldreads,
Perfstat. Stats $ sysstat newreads,
Perfstat. Stats $ sysstat oldwrites,
Perfstat. Stats $ sysstat newwrites,
Perfstat. Stats $ snapshot Sn
Where newreads. snap_id = Sn. snap_id
And newwrites. snap_id = Sn. snap_id
And oldreads. snap_id = Sn. snap_id-1
And oldwrites. snap_id = Sn. snap_id-1
And oldreads. Statistic # = 42 -- 42 physical reads
And newreads. Statistic # = 42
And oldwrites. Statistic # = 46 -- 46 physical writes
And newwrites. Statistic # = 46
And (newreads. Value-oldreads. Value)> 0
And (newwrites. Value-oldwrites. Value)> 0
And snap_time> to_date ('2017-07-08 18:00:00 ', 'yyyy-mm-dd hh24: MI: ss ')
;

-- Buffer hit rate
Select substr (to_char (snap_time, 'yyyy-mm-dd hh24: Mi'), 12 ),
Round (100 * (A. Value-E. Value) + (B. Value-F. Value ))-
(C. Value-G. Value ))/
(A. Value-E. Value) + (B. Value-F. Value) "buffer hit ratio"
From perfstat. Stats $ sysstat,
Perfstat. Stats $ sysstat B,
Perfstat. Stats $ sysstat C,
Perfstat. Stats $ sysstat D,
Perfstat. Stats $ sysstat e,
Perfstat. Stats $ sysstat F,
Perfstat. Stats $ sysstat G,
Perfstat. Stats $ snapshot Sn
Where a. snap_id = Sn. snap_id
And B. snap_id = Sn. snap_id
And C. snap_id = Sn. snap_id
And D. snap_id = Sn. snap_id
And E. snap_id = Sn. snap_id-1
And F. snap_id = Sn. snap_id-1
And G. snap_id = Sn. snap_id-1
And a. Statistic # = 40
And E. Statistic # = 40
And B. Statistic # = 41
And F. Statistic # = 41
And C. Statistic # = 42
And G. Statistic # = 42
And D. Statistic # = 46
And snap_time> to_date ('2017-07-08 18:00:00 ', 'yyyy-mm-dd hh24: MI: ss ')
;
/*
40 dB block gets
41 consistent gets
42 physical reads
46 physical writes
*/
-- Buffer hit rate calculation formula
Formula 1:
Select name,
(Consistent_gets + db_block_gets)-physical_reads )/
(Consistent_gets + db_block_gets) * 100 "hit ratio %"
From v $ buffer_pool_statistics
Where physical_reads> 0 ;?
Formula 2:
Hit ratio = 1-(physical reads-physical reads direct (LOB ))/
(Db block gets + consistent gets-physical reads direct (LOB ))
Formula 3:
Hit ratio = 1-[physical reads/(block gets + consistent gets)]

Select name,
Physical_reads,
Db_block_gets,
Consistent_gets,
1-(physical_reads/(db_block_gets + consistent_gets) "hit ratio"
From v $ buffer_pool_statistics
Where name = 'default ';