一,外部表介绍
Greenplum 在数据加载上有一个明显的优势,就是支持数据的并发加载,gpfdisk是并发加载的工具,数据库中对应的就是外部表
所谓外部表，就是在数据库中只有表定义、没有数据，数据都存放在数据库之外的数据文件。greenplum可以对一个外部表执行正常的DML操作，当读取数据的时候，数据库从数据文件中加载数据。外部表支持在segment上并发地告诉从gpfdist导入数据，由于是从segment上导入数据，所以效率很高。
结构图:
外部表需要指定gpfdist的IP和端口，还要有详细的目录地址，文件名支持通配符匹配。可以编写多个gpfdist地址，但是总数不能超过总的segment数量，否则会报错。
GPDB提供两种外部表：可读外部表用于数据装载、可写外部表用于数据卸载。外部表可基于文件、亦可基于WEB，这两种都能实现可读、可写。
当一个查询使用一个常规的外部表，该外部表被认为是可重读的，因为在该查询期间数据是静态的。而对于WEB外部表，数据是不可重读的，因为在该查询的执行期间数据可能会发生变化。
可写外部表用以从数据库表中选择记录并输出到文件、命名管道或其他可执行程序。 比如，可以从GPDB中卸载数据并发送到一个可执行程序，该程序连接到其他数据库或者ETL工具并装载数据到其他地方。 可写外部表还可以用于输出到GPDB的并行MapReduce计算。
可写外部表被定义后，数据即可从数据库表中被选择并插入到该可写外部表。 可写外部表只允许INSERT操作 – SELECT、 UPDATE、 DELETE或TRUNCATE是不允许的。可写外部表输出数据到一个可执行程序，该程序要能够接受流输入数据。
在创建外部表的时候，可以指定分隔符、err表、指定允许出错的数据条数，以及源文件的编码等信息。
二,外部表语法
CREATE [READABLE] EXTERNAL TABLE table_name
( column_name data_type [, ...] | LIKE other_table )
LOCATION ('file://seghost[:port]/path/file' [, ...])
| ('gpfdist://filehost[:port]/file_pattern[#transform]'
| ('gpfdists://filehost[:port]/file_pattern[#transform]'
[, ...])
| ('gphdfs://hdfs_host[:port]/path/file')
FORMAT 'TEXT'
[( [HEADER]
[DELIMITER [AS] 'delimiter' | 'OFF']
[NULL [AS] 'null string']
[ESCAPE [AS] 'escape' | 'OFF']
[NEWLINE [ AS ] 'LF' | 'CR' | 'CRLF']
[FILL MISSING FIELDS] )]
| 'CSV'
[( [HEADER]
[QUOTE [AS] 'quote']
[DELIMITER [AS] 'delimiter']
[NULL [AS] 'null string']
[FORCE NOT NULL column [, ...]]
[ESCAPE [AS] 'escape']
[NEWLINE [ AS ] 'LF' | 'CR' | 'CRLF']
[FILL MISSING FIELDS] )]
| 'AVRO'
| 'PARQUET' | 'CUSTOM' (Formatter=<formatter specifications>)
[ ENCODING 'encoding' ]
[ [LOG ERRORS [INTO error_table]] SEGMENT REJECT LIMIT count
[ROWS | PERCENT] ] CREATE [READABLE] EXTERNAL WEB TABLE table_name
( column_name data_type [, ...] | LIKE other_table )
LOCATION ('http://webhost[:port]/path/file' [, ...])
| EXECUTE 'command' [ON ALL
| MASTER
| number_of_segments
| HOST ['segment_hostname']
| SEGMENT segment_id ]
FORMAT 'TEXT'
[( [HEADER]
[DELIMITER [AS] 'delimiter' | 'OFF']
[NULL [AS] 'null string']
[ESCAPE [AS] 'escape' | 'OFF']
[NEWLINE [ AS ] 'LF' | 'CR' | 'CRLF']
[FILL MISSING FIELDS] )]
| 'CSV'
[( [HEADER]
[QUOTE [AS] 'quote']
[DELIMITER [AS] 'delimiter']
[NULL [AS] 'null string']
[FORCE NOT NULL column [, ...]]
[ESCAPE [AS] 'escape']
[NEWLINE [ AS ] 'LF' | 'CR' | 'CRLF']
[FILL MISSING FIELDS] )]
| 'CUSTOM' (Formatter=<formatter specifications>)
[ ENCODING 'encoding' ]
[ [LOG ERRORS [INTO error_table]] SEGMENT REJECT LIMIT count
[ROWS | PERCENT] ] CREATE WRITABLE EXTERNAL TABLE table_name
( column_name data_type [, ...] | LIKE other_table )
LOCATION('gpfdist://outputhost[:port]/filename[#transform]'
| ('gpfdists://outputhost[:port]/file_pattern[#transform]'
[, ...])
| ('gphdfs://hdfs_host[:port]/path')
FORMAT 'TEXT'
[( [DELIMITER [AS] 'delimiter']
[NULL [AS] 'null string']
[ESCAPE [AS] 'escape' | 'OFF'] )]
| 'CSV'
[([QUOTE [AS] 'quote']
[DELIMITER [AS] 'delimiter']
[NULL [AS] 'null string']
[FORCE QUOTE column [, ...]] ]
[ESCAPE [AS] 'escape'] )]
| 'AVRO'
| 'PARQUET' | 'CUSTOM' (Formatter=<formatter specifications>)
[ ENCODING 'write_encoding' ]
[ DISTRIBUTED BY (column, [ ... ] ) | DISTRIBUTED RANDOMLY ] CREATE WRITABLE EXTERNAL WEB TABLE table_name
( column_name data_type [, ...] | LIKE other_table )
EXECUTE 'command' [ON ALL]
FORMAT 'TEXT'
[( [DELIMITER [AS] 'delimiter']
[NULL [AS] 'null string']
[ESCAPE [AS] 'escape' | 'OFF'] )]
| 'CSV'
[([QUOTE [AS] 'quote']
[DELIMITER [AS] 'delimiter']
[NULL [AS] 'null string']
[FORCE QUOTE column [, ...]] ]
[ESCAPE [AS] 'escape'] )]
| 'CUSTOM' (Formatter=<formatter specifications>)
[ ENCODING 'write_encoding' ]
[ DISTRIBUTED BY (column, [ ... ] ) | DISTRIBUTED RANDOMLY ]
三,创建外部表
01,语法
gpfdist [-d directory] [-p http_port] [-l log_file] [-t timeout]
[-S] [-w time] [-v | -V] [-s] [-m max_length] [--ssl certificate_path]
gpfdist -? | --help
gpfdist --version
02,启动进程
--创建gpdist进程
[gpadmin@greenplum02 ~]$ mkdir script
[gpadmin@greenplum02 ~]$ nohup gpfdist -d /home/gpadmin/script/ -p 8081 -l /home/gpadmin/script/gpfdist.log &
[] 6904
[gpadmin@greenplum02 ~]$ nohup: ignoring input and appending output to ‘nohup.out’
[gpadmin@greenplum02 ~]$ ss -lntup|grep 8081
tcp LISTEN 0 128 :::8081 :::* users:(("gpfdist",pid=6904,fd=6))
---配置读取文件
[gpadmin@greenplum02 script]$ cat test.txt
Prague,Jan,101,4875.33
Rome,Mar,87,1557.39
Bangalore,May,317,8936.99
Beijing,Jul,411,11600.67
San Francisco,Sept,156,6846.34
Paris,Nov,159,7134.56
San Francisco,Jan,113,5397.89
Prague,Dec,333,9894.77
Bangalore,Jul,271,8320.55
Beijing,Dec,100,4248.41 q
[gpadmin@greenplum02 script]$ pwd
/home/gpadmin/script
--后面的是错误信息
03,创建外部表
create external table public.test
(
country varchar(128),
name varchar(128),
id int,
sale varchar(128)
)
location ('gpfdist://192.168.0.222:8081/test.txt')
format 'text'
(delimiter ',' null as '' escape 'off')
encoding 'utf8'
log error segment reject limit 3 rows; --- location 文件所在位置，可以直接是本地路径、gpfdist地址、gpfdists地址、gphdfs地址。
--- format 文本类型
--- delimiter 分隔符
--- encoding 编码
--- log error into 错误数据表，记录错误数据，会自动创建。一般都是tablename_err格式，例如t1_err。
--- segment reject limit 错误数据的条数/百分比(rows/percent)，超过设置值会报错。最小值是2。用来确保数据的完整性。
结果:
postgres=# create external table public.test99(country varchar(128),name varchar(128),id int,sale varchar(128))location ('gpfdist://192.168.0.222:8081/test.txt')format 'text'(delimiter ',' null as '' escape 'off')encoding 'utf8'log errors segment reject limit 3 rows;
CREATE EXTERNAL TABLE
postgres=# SELECT * from public.test99
postgres-# ;
NOTICE: Found 2 data formatting errors (2 or more input rows). Rejected related input data.
country | name | id | sale
---------------+------+-----+----------
Prague | Jan | 101 | 4875.33
Rome | Mar | 87 | 1557.39
Bangalore | May | 317 | 8936.99
Beijing | Jul | 411 | 11600.67
San Francisco | Sept | 156 | 6846.34
Paris | Nov | 159 | 7134.56
San Francisco | Jan | 113 | 5397.89
Prague | Dec | 333 | 9894.77
Bangalore | Jul | 271 | 8320.55
Beijing | Dec | 100 | 4248.41
(10 rows) postgres=# SELECT * from test99;
NOTICE: Found 2 data formatting errors (2 or more input rows). Rejected related input data.
country | name | id | sale
---------------+------+-----+----------
Prague | Jan | 101 | 4875.33
Rome | Mar | 87 | 1557.39
Bangalore | May | 317 | 8936.99
Beijing | Jul | 411 | 11600.67
San Francisco | Sept | 156 | 6846.34
Paris | Nov | 159 | 7134.56
San Francisco | Jan | 113 | 5397.89
Prague | Dec | 333 | 9894.77
Bangalore | Jul | 271 | 8320.55
Beijing | Dec | 100 | 4248.41
(10 rows)
04,数据装载
insert into table select * from table_ext; 内部表<----外部表