Query performance slow in one instance in RAC

Question

Hi
We have 3 node RAC. When we test onw query it slow by 40% in one instance and always physical reads are hapenning in that instance.
Below are the details. All the parameters are same. Users compains some times the query is slow.
Thanks in Advance.
From Instance 1 - 9 Sec
=============================================================
Statistics
          0  recursive calls
          1  db block gets
      67209  consistent gets
          0  physical reads
          0  redo size
      23465  bytes sent via SQL*Net to client
      10356  bytes received via SQL*Net from client
         28  SQL*Net roundtrips to/from client
          1  sorts (memory)
          0  sorts (disk)
         13  rows processed
From Instance 2 - 13 Sec
=============================================================
Statistics
          0  recursive calls
          1  db block gets
      67215  consistent gets
      67193  physical reads    <<------------------------ Only in one instance
          0  redo size
      23465  bytes sent via SQL*Net to client
      10356  bytes received via SQL*Net from client
         28  SQL*Net roundtrips to/from client
          1  sorts (memory)
          0  sorts (disk)
         13  rows processed
From Instance 3 - 9 Sec
=============================================================
Statistics
          0  recursive calls
          1  db block gets
      67209  consistent gets
          0  physical reads
          0  redo size
      23465  bytes sent via SQL*Net to client
      10356  bytes received via SQL*Net from client
         28  SQL*Net roundtrips to/from client
          1  sorts (memory)
          0  sorts (disk)
         13  rows processed

Answer 1

You can also check global cache statistics. Run this before and after your query :
select name, value from v$mystat s, v$statname n where s.statistic#=n.statistic# and name like '%blocks received';