a lot of shared buffers hit when planning for a simple query with primary access path

Hi,
   a simple SQL "select ... from tablex where id1=34215670 and
id2=59403938282;
id1 and i2 are bigint and primary key.
      Index Cond: ((tablex.id2 = ' 5940393828299'::bigint) AND (tablex.id1
= ' 34215670  '::bigint))
   Buffers: shared hit=2
 Query Identifier: -1350604566224020319
 Planning:
   Buffers: shared hit=110246         <<< here planning need access a lot
of buffers
 Planning Time: 81.850 ms
 Execution Time: 0.034 ms

   could you help why planning need a lot of shared buffers access ?  this
table has 4 indexes.  and I tested similar SQL with another table has 4
compound indexes and that table only show very small shared buffers hit
when planning.
   this table has a lot of  "update" and "delete" .

Thanks,

James