Inconsistency between pg_stat_activity and log_duration

I found an interesting inconsistency between pg_stat_activity and
log_duration.

-[ RECORD 1 ]----+---------------------------------------------------------------------------------------------------------------------------
datid | 16392
datname | test
pid | 21815
usesysid | 10
usename | t-ishii
application_name | psql
client_addr |
client_hostname |
client_port | -1
backend_start | 2014-02-04 12:46:55.178688+09
xact_start | 2014-02-04 12:47:27.210976+09
query_start | 2014-02-04 12:47:27.210976+09
state_change | 2014-02-04 12:47:27.210981+09
waiting | f
state | active
query | select * from pg_stat_activity;

[snip]

-[ RECORD 3 ]----+---------------------------------------------------------------------------------------------------------------------------
datid | 16392
datname | test
pid | 21850
usesysid | 10
usename | t-ishii
application_name | pgbench
client_addr |
client_hostname |
client_port | -1
backend_start | 2014-02-04 12:47:11.233245+09
xact_start | 2014-02-04 12:47:11.235236+09
query_start | 2014-02-04 12:47:11.241084+09
state_change | 2014-02-04 12:47:11.241085+09
waiting | f
state | active
query | SELECT count(*) FROM pg_catalog.pg_class AS c WHERE c.oid = pgpool_regclass('pgbench_accounts') AND c.relpersistence = 'u'

As you can see, at 2014-02-04 12:47:27.210981+09 the query "SELECT
count(*) FROM pg_catalog.pg_class..." is "active" and it seems still
running.

On the other side, Here is an excerpt from PostgreSQL log:

21850 2014-02-04 12:47:11.241 JST LOG: execute pgpool21805/pgpool21805: SELECT count(*) FROM pg_catalog.pg_class AS c WHERE c.oid = pgpool_regclass('pgbench_accounts') AND c.relpersistence = 'u'
21850 2014-02-04 12:47:11.241 JST LOG: duration: 0.078 ms

The duration was shown as "0.078 ms" thus it seems the query has been
already finished.

The reason why pg_stat_activity thinks that the query in question is,
"sync" message has not been sent to the backend yet (at least from
what I read from postgres.c).

I think this inconsistency is not very intutive to users...

Best regards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese: http://www.sraoss.co.jp