too high planning time

I have a problem with the explain analyze' output of some queries. There is too high planning time, but the execution time is relatively low. What is the possible reason behind this problem? I also ran the vacuum and analyze commands for the table. 

EXPLAIN ANALYZE select  
    i."DefinitionId",
from
    "T_WF_INSTANCE" i
where
    i."InstanceId" = 10045683193;
                                                                                   QUERY PLAN                                                                                  
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Index Scan using "T_WF_INSTANCE_InstanceId_ApplicationCd_EntityStatusCd_idx" on "T_WF_INSTANCE" i  (cost=0.57..2.79 rows=1 width=34) (actual time=2.522..2.522 rows=1 loops=1)
   Index Cond: ("InstanceId" = '10045683193'::bigint)
 Planning Time: 8460.446 ms
 Execution Time: 2.616 ms
(4 rows)

Thank you,

Kenny