greenplum_externaltable_error_http_code_404

开发反馈在使用外部表的时候遇到ERROR:  http response code 404错误，经过测试和模拟得以解决。
首先模拟下问题：
[gpadmin@gtlions50 ~]$ psql gtlions
psql (8.2.15)
Type "help" for help.

gtlions=# drop external table ext_rt_recv_msg_gprs;
ERROR:  table "ext_rt_recv_msg_gprs" does not exist
gtlions=# drop table ext_err_rt_recv_msg_gprs;
ERROR:  table "ext_err_rt_recv_msg_gprs" does not exist
gtlions=# create external table ext_rt_recv_msg_gprs
gtlions-# ( recv_time timestamp,
gtlions(#   trigger_type int,
gtlions(#   rating_group bigint,
gtlions(#   session_id varchar(80),
gtlions(#   mscc_count int )
gtlions-# location
gtlions-# ( 'gpfdist://192.168.56.10:8081/1/*',
gtlions(#   'gpfdist://192.168.56.10:8081/2/*' )
gtlions-# format 'text' ( delimiter '|' null '')
gtlions-# encoding 'gbk'
gtlions-# log errors into ext_err_rt_recv_msg_gprs
gtlions-# segment reject limit 100 percent;
NOTICE:  Error table "ext_err_rt_recv_msg_gprs" does not exist. Auto generating an error table with the same name
CREATE EXTERNAL TABLE
gtlions=# select * from ext_rt_recv_msg_gprs;
ERROR:  http response code 404 from gpfdist (gpfdist://192.168.56.10:8081/2/*): HTTP/1.0 404 file not found (url.c:326)  (seg1 slice1 gtlions52:40001 pid=2584) (cdbdisp.c:1476)
经过测试，使用linux网络工具是可以正确获取到文件的，因此怀疑是SQL语句有问题，尝试如下：
gtlions=# drop external table ext_rt_recv_msg_gprs;
DROP EXTERNAL TABLE
gtlions=# drop table ext_err_rt_recv_msg_gprs;
DROP TABLE
gtlions=# drop external table if exists ext_rt_recv_msg_gprs;
NOTICE:  table "ext_rt_recv_msg_gprs" does not exist, skipping
DROP EXTERNAL TABLE
gtlions=# drop table  if exists ext_err_rt_recv_msg_gprs;
NOTICE:  table "ext_err_rt_recv_msg_gprs" does not exist, skipping
DROP TABLE
gtlions=# create external table ext_rt_recv_msg_gprs
gtlions-# ( recv_time timestamp,
gtlions(#   trigger_type int,
gtlions(#   rating_group bigint,
gtlions(#   session_id varchar(80),
gtlions(#   mscc_count int )
gtlions-# location
gtlions-# ( 'gpfdist://192.168.56.10:8081/*/*')
gtlions-# format 'text' ( delimiter '|' null '')
gtlions-# encoding 'gbk'
gtlions-# log errors into ext_err_rt_recv_msg_gprs
gtlions-# segment reject limit 100 percent;
NOTICE:  Error table "ext_err_rt_recv_msg_gprs" does not exist. Auto generating an error table with the same name
CREATE EXTERNAL TABLE
gtlions=# select * from ext_rt_recv_msg_gprs;
         recv_time          | trigger_type | rating_group |        session_id         | mscc_count
----------------------------+--------------+--------------+---------------------------+------------
 2014-03-24 23:59:56.123456 |          251 |        25111 | 25tst_ext_data_table row1 |     503001
 2014-03-25 16:11:36.123    |          252 |        25222 | 25tst_ext_data_table row2 |     503002
 2014-03-25 16:11:36        |          253 |        25333 | 25tst_ext_data_table row3 |     503003
 2014-03-25 16:11:36.123456 |          254 |        25444 | 25tst_ext_data_table row4 |     503004
 2014-03-25 16:11:36.223456 |          255 |        25555 | 25tst_ext_data_table row5 |     503005
 2014-03-25 16:11:36.323456 |          256 |        25666 | 25tst_ext_data_table row6 |     503006
 2014-03-25 00:00:00        |          257 |        25777 | 25tst_ext_data_table row7 |           
(7 rows)

gtlions=# drop external table if exists ext_rt_recv_msg_gprs;
DROP EXTERNAL TABLE
gtlions=# drop table  if exists ext_err_rt_recv_msg_gprs;
DROP TABLE
gtlions=# create external table ext_rt_recv_msg_gprs
gtlions-# ( recv_time timestamp,
gtlions(#   trigger_type int,
gtlions(#   rating_group bigint,
gtlions(#   session_id varchar(80),
gtlions(#   mscc_count int )
gtlions-# location
gtlions-# ( 'gpfdist://192.168.56.10:8081/*')
gtlions-# format 'text' ( delimiter '|' null '')
gtlions-# encoding 'gbk'
gtlions-# log errors into ext_err_rt_recv_msg_gprs
gtlions-# segment reject limit 100 percent;
NOTICE:  Error table "ext_err_rt_recv_msg_gprs" does not exist. Auto generating an error table with the same name
CREATE EXTERNAL TABLE
gtlions=# select * from ext_rt_recv_msg_gprs;
         recv_time          | trigger_type | rating_group |        session_id         | mscc_count
----------------------------+--------------+--------------+---------------------------+------------
 2014-03-24 23:59:56.123456 |          251 |        25111 | 25tst_ext_data_table row1 |     503001
 2014-03-25 16:11:36.123    |          252 |        25222 | 25tst_ext_data_table row2 |     503002
 2014-03-25 16:11:36        |          253 |        25333 | 25tst_ext_data_table row3 |     503003
 2014-03-25 16:11:36.123456 |          254 |        25444 | 25tst_ext_data_table row4 |     503004
 2014-03-25 16:11:36.223456 |          255 |        25555 | 25tst_ext_data_table row5 |     503005
 2014-03-25 16:11:36.323456 |          256 |        25666 | 25tst_ext_data_table row6 |     503006
 2014-03-25 00:00:00        |          257 |        25777 | 25tst_ext_data_table row7 |           
(7 rows)
ok了，问题解决了，原来是同一个url不能出现多次的原因。
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