Large time difference between explain analyze and normal run - Mailing list pgsql-performance

Does anyone have any idea why there be over a 4s difference between running
the statement directly and using explain analyze?  Multiple runs give the
same result and I've tested on several servers.

db=# \timing
Timing is on.
db=# select count(*) from answer;
 count
--------
 530576
(1 row)

Time: 358.805 ms
db=# explain analyze select count(*) from answer;
                                                      QUERY PLAN
----------------------------------------------------------------------------------------------------------------------
 Aggregate  (cost=9848.12..9848.12 rows=1 width=0) (actual
time=4841.231..4841.235 rows=1 loops=1)
   ->  Seq Scan on answer  (cost=0.00..8561.29 rows=514729 width=0) (actual
time=0.011..2347.762 rows=530576 loops=1)
 Total runtime: 4841.412 ms
(3 rows)

Time: 4855.712 ms

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Postgresql 7.4.5 running on Linux 2.6.8.1