直连greenplum segment节点的方法, utility模式 :
使用这种方式，不与其他节点通讯，只操作当前节点。也没有数据分布的概念。
如果使用utility模式连接的是master节点，写入数据时，数据不会分布到segment，使用正常模式连接后，写入master的数据也查不出来。
$ PGOPTIONS='-c gp_session_role=utility' psql -p 40005
psql (8.2.15)
Type "help" for help.
postgres=# \dt
List of relations
Schema | Name | Type | Owner | Storage
--------+------+-------+----------+---------
public | t | table | digoal | heap
public | test | table | digoal | heap
(2 rows)
postgres=# select * from pg_locks;
locktype | database | relation | page | tuple | transactionid | classid | objid | objsubid | transaction | pid | mode | granted | mppsessionid | mppiswriter | gp_segment_id
---------------+----------+----------+------+-------+---------------+---------+-------+----------+-------------+--------+-----------------+---------+--------------+-------------+---------------
transactionid | | | | | 136604 | | | | 136604 | 130724 | ExclusiveLock | t | 6 | t | -1
relation | 10899 | 10333 | | | | | | | 136604 | 130724 | AccessShareLock | t | 6 | t | -1
(2 rows)
注意使用PGOPTIONS='-c gp_session_role=utility'后，只操作本地节点
$psql -p # master
psql (8.2.15)
Type "help" for help.
postgres=# select count(*) from test;
count
-------
0
(1 row)
postgres=# \q
$psql -p 40001 # segment
psql (8.2.15)
Type "help" for help.
postgres=# select count(*) from test;
count
---------
4166801
(1 row)
