GPDB管理员笔记(三)装载和卸载数据

外部表定义
可读外部表(不可以做dml操作)
可写外部表(只insert,不可以select,update,delete)

装载
创建外部表
=# CREATE EXTERNAL WEB TABLE ext_expenses (name text,
date date, amount float4, category text, description text)
LOCATION ( ‘http://intranet.company.com/expenses/sales/file.csv‘,
‘http://intranet.company.com/expenses/exec/file.csv‘,
‘http://intranet.company.com/expenses/finance/file.csv‘,
‘http://intranet.company.com/expenses/ops/file.csv‘,
‘http://intranet.company.com/expenses/marketing/file.csv‘,
‘http://intranet.company.com/expenses/eng/file.csv‘ )
FORMAT ‘CSV‘ ( HEADER );

装载外部表数据
=# INSERT INTO expenses_travel
SELECT * from ext_expenses where category=‘travel‘;
或者想要快速装载全部数据到一个新的数据库表中:
=# CREATE TABLE expenses AS SELECT * from ext_expenses;

测试:
[root@mdw ~]# wget http://mirrors.aliyun.com/repo/Centos-6.repo
--2014-03-04 13:51:30--  http://mirrors.aliyun.com/repo/Centos-6.repo
正在解析主机 mirrors.aliyun.com... 115.28.122.210, 112.124.140.210
正在连接 mirrors.aliyun.com|115.28.122.210|:80... 已连接。
已发出 HTTP 请求,正在等待回应... 200 OK
长度:2086 (2.0K) [application/octet-stream]
正在保存至: “Centos-6.repo”

100%[==============================================================================================================================>] 2,086       --.-K/s   in 0s     

2014-03-04 13:51:30 (194 MB/s) - 已保存 “Centos-6.repo” [2086/2086])


libo=# CREATE EXTERNAL WEB TABLE ext_expenses (name text)
libo-# location (‘http://mirrors.aliyun.com/repo/Centos-6.repo‘)
libo-#  FORMAT ‘TEXT‘ ( DELIMITER ‘|‘ NULL ‘ ‘) ;
CREATE EXTERNAL TABLE
libo=# CREATE TABLE expenses AS SELECT * from ext_expenses;
NOTICE:  Table doesn‘t have ‘DISTRIBUTED BY‘ clause -- Using column(s) named ‘colum‘ as the Greenplum Database data distribution key for this table.
HINT:  The ‘DISTRIBUTED BY‘ clause determines the distribution of data. Make sure column(s) chosen are the optimal data distribution key to minimize skew.
ERROR:  could not translate host name "mirrors.aliyun.com", port "80" to address: Temporary failure in name resolution (cdbutil.c:754)  (seg0 slice1 sdw1:40000 pid=26261) (cdbdisp.c:1489)
libo=#
libo=#
libo=# SELECT * from ext_expenses;
ERROR:  could not translate host name "mirrors.aliyun.com", port "80" to address: Temporary failure in name resolution (cdbutil.c:754)  (seg0 slice1 sdw1:40000 pid=26254) (cdbdisp.c:1489)

libo=# drop EXTERNAL WEB TABLE ext_expenses ;
DROP EXTERNAL TABLE
libo=# CREATE EXTERNAL WEB TABLE ext_expenses  (colum text)
libo-# location (‘http://115.28.122.210/repo/Centos-6.repo‘)
libo-# FORMAT ‘TEXT‘ ( DELIMITER ‘|‘ NULL ‘ ‘) ;
CREATE EXTERNAL TABLE
libo=# select * from ext_expenses;
ERROR:  connection with gpfdist failed for http://115.28.122.210/repo/Centos-6.repo. effective url: http://115.28.122.210/repo/Centos-6.repo.  (seg0 slice1 sdw1:40000 pid=26296)
libo=#




[gpadmin@mdw data_tst]$ gpfdist -d /home/gpadmin/data_tst -p 8081  -l /home/gpadmin/log1 &
[1] 10321
[gpadmin@mdw data_tst]$ Serving HTTP on port 8081, directory /home/gpadmin/data_tst

[root@mdw ~]# wget http://192.168.100.101:8081/aaa
--2014-03-04 14:14:01--  http://192.168.100.101:8081/aaa
正在连接 192.168.100.101:8081... 已连接。
已发出 HTTP 请求,正在等待回应... 200 ok
长度:未指定 [text/plain]
正在保存至: “aaa”

    [ <=>                                                                                                                           ] 17          --.-K/s   in 0s     

2014-03-04 14:14:01 (1.61 MB/s) - “aaa” 已保存 [17]

libo=# CREATE EXTERNAL WEB TABLE ext_expenses  (colum text)
libo-# location (‘http://192.168.100.101:8081/aaa‘)
libo-# FORMAT ‘TEXT‘ ( DELIMITER ‘|‘ NULL ‘ ‘) ;
CREATE EXTERNAL TABLE
libo=# select * from ext_expenses;
colum
-------
aaaa
aaa

aa
a


(7 rows)


 create table t as select * from t_ext DISTRIBUTED BY(id);

libo=# create table t as select * from t_ext DISTRIBUTED RANDOMLY;
SELECT 10


libo=# create external table t_ext (id int,name text)
libo-# location (‘gpfdist://192.168.100.11:8081/aaa.csv‘)
libo-# format ‘csv‘;
CREATE EXTERNAL TABLE
libo=# select * from t_ext;
ERROR:  missing data for column "name"  (seg3 slice1 sdw2:40001 pid=10243)
DETAIL:  External table t_ext, line 4000 of gpfdist://192.168.100.11:8081/aaa.csv: ""

原因:csv 中有空行

结论:外部表只支持gpfdist 的http协议 gpfdist服务是GP的简单的web服务


装载错误处理:
在定义可读外部表时使用CREATE EXTERNAL TABLE命令
结合使用SEGMENT REJECT LIMIT子句。
  拒绝限制count参数可用于指定记录数(缺省),或者使用PERCENT指定记录
百分比。
  保存错误记录以备将来的检查,使用LOG ERRORS INTO子句指定错误记
录日志表。


使用gpload装载

卸载数据

禁止web表定义中使用execute
libo=# show gp_external_enable_exec
libo-# ;
gp_external_enable_exec
-------------------------
on
(1 row)

数据格式

在使用各种GP命令装载或卸载数据时,需要指定数据如何格式化

行分隔
GPDB预期是以LF字符(Line Feed/换行符/0x0A)、CR(Carriage Return/回车/0x0D)
或者CR加LF(CR+LF/回车换行/0x0A 0x0D)作为一行的分割。LF是标准UNIX或
类UNIX操作系统的标准换行标识符。其他操作系统(如Windows、Mac OS 9)可
能是CR或者CR+LF。所有这些换行标识符在GPDB中都被支持作为行分隔符

列分隔
对于TEXT文件来说缺省的列分隔符是TAB字符(0x09),而 对 于CSV文件来说缺
省的列分隔符是逗号(0x2C)。不过在使用COPY、CREATE EXTERNAL TABLE
时或者使用gpload定义数据格式时都可以使用DELIMITER子句执行其他的单
字符分隔符。



 

GPDB管理员笔记(三)装载和卸载数据,古老的榕树,5-wow.com

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