Author: 义从
总所周知,阿里云的 PostgreSQL 和 HybridDB for PostgreSQL 和 oss 是全面互通的。 HybridDB for PostgreSQL 由于是 MPP 架构天生包括多个计算节点,能够以为并发的方式读写 oss 上的数据。PostgreSQL 在这方面要差一点,默认情况下只能单进程读写 OSS,不过通过 dblink 的加持,我们也能让 OSS 中的数据快速装载到 PostgreSQL。本文就给大家讲讲这其中的黑科技。
首先,创建我们要用到的插件。
create extension dblink;
create extension oss_fdw;
-- 异步数据装载的准备工作
CREATE OR REPLACE FUNCTION rds_oss_fdw_load_data_prepare(t_from text, t_to text)
RETURNS bool AS
$BODY$
DECLARE
t_exist int;
curs1 refcursor;
r record;
filepath text;
fileindex int8;
s1 text;
s2 text;
s3 text;
c int = 0;
s4 text;
s5 text;
ss4 text;
ss5 text;
sql text;
BEGIN
create table if not exists oss_fdw_load_status(id BIGSERIAL primary key, filename text, size int8, rows int8 default 0, status int default 0);
select count(*) into t_exist from oss_fdw_load_status;
if t_exist != 0 then
RAISE NOTICE 'oss_fdw_load_status not empty';
return false;
end if;
-- 通过 oss_fdw_list_file 函数,把外部表 t_from 匹配的 OSS 中的文件列到表中
insert into oss_fdw_load_status (filename, size) select name,size from oss_fdw_list_file(t_from) order by size desc;
select count(*) into t_exist from oss_fdw_load_status;
if t_exist = 0 then
RAISE NOTICE 'oss_fdw_load_status empty,not task found';
return false;
end if;
return true;
END;
$BODY$
LANGUAGE plpgsql;
-- 数据装载的工作函数
CREATE OR REPLACE FUNCTION rds_oss_fdw_load_data_execute(t_from text, t_to text, num_work int, pass text)
RETURNS bool AS
$BODY$
DECLARE
t_exist int;
curs1 refcursor;
r record;
filepath text;
fileindex int8;
s1 text;
s2 text;
s3 text;
c int = 0;
s4 text;
s5 text;
ss4 text;
ss5 text;
sql text;
db text;
user text;
BEGIN
select count(*) into t_exist from oss_fdw_load_status;
if t_exist = 0 then
RAISE NOTICE 'oss_fdw_load_status empty';
return false;
end if;
s4 = 'oss_loader';
s5 = 'idle';
ss4 = '''' || s4 ||'''';
ss5 = '''' || s5 ||'''';
sql = 'select count(*) from pg_stat_activity where application_name = ' || ss4 || ' and state != ' || ss5;
select current_database() into db;
select current_user into user;
-- 通过游标,不断获取单个任务
OPEN curs1 FOR SELECT id, filename FROM oss_fdw_load_status order by id;
loop
fetch curs1 into r;
if not found then
exit;
end if;
fileindex = r.id;
filepath = r.filename;
s1 = '''' || t_from ||'''';
s2 = '''' || t_to ||'''';
s3 = '''' || filepath ||'''';
LOOP
-- 查看当前正在工作的任务数,过达到并发数就在这里等待
select a into c from dblink('dbname='||db ||' user='||user || ' password='||pass ,sql)as t(a int);
IF c < num_work THEN
EXIT;
END IF;
RAISE NOTICE 'current runing % loader', c;
perform pg_sleep(1);
END LOOP;
-- 通过 DBLINK 创建异步任务
perform dis_conn('oss_loader_'||fileindex);
perform dblink_connect('oss_loader_'||fileindex, 'dbname='||db ||' user='||user || ' application_name=oss_loader' || ' password='||pass);
perform dblink_send_query('oss_loader_'||fileindex, format('
begin;
select rds_oss_fdw_load_single_file(%s,%s,%s,%s);
end;'
, fileindex, s1, s2, s3)
);
RAISE NOTICE 'runing loader task % filename %',fileindex, filepath;
end loop;
close curs1;
-- 任务分配完成,等待所有任务完成
LOOP
select a into c from dblink('dbname='||db ||' user='||user || ' password='||pass ,sql)as t(a int);
IF c = 0 THEN
EXIT;
END IF;
RAISE NOTICE 'current runing % loader', c;
perform pg_sleep(1);
END LOOP;
return true;
END;
$BODY$
LANGUAGE plpgsql;
-- 单个文件的数据装在函数
CREATE OR REPLACE FUNCTION rds_oss_fdw_load_single_file(taskid int8, t_from text, t_to text, filepath text)
RETURNS void AS
$BODY$
DECLARE
rowscount int8 = 0;
current text;
sql text;
BEGIN
-- 配置 GUC 参数,指定要导入的 OSS 上的文件
perform set_config('oss_fdw.rds_read_one_file',filepath,true);
select current_setting('oss_fdw.rds_read_one_file') into current;
RAISE NOTICE 'begin load %', current;
-- 通过动态 SQL 导入数据
EXECUTE 'insert into '|| t_to || ' select * from ' || t_from;
GET DIAGNOSTICS rowscount = ROW_COUNT;
-- 导入完成后,把结果保存到状态表中
RAISE NOTICE 'end load id % % to % % rows', taskid, filepath, t_to, rowscount;
update oss_fdw_load_status set rows = rowscount,status = 1 where id = taskid;
return;
EXCEPTION
when others then
RAISE 'run rds_oss_fdw_load_single_file with error';
END;
$BODY$
LANGUAGE plpgsql;
-- 关闭连接不报错
create or replace function dis_conn(name) returns void as $$
declare
begin
perform dblink_disconnect($1);
return;
exception when others then
return;
end;
$$ language plpgsql strict;
select rds_oss_fdw_load_data_prepare('oss_table','lineitem');
执行后,会看到表 oss_fdw_load_status 中,保存了准备导入的所有文件列表,用户可以做适当的删减定制。
select rds_oss_fdw_load_data_execute('oss_table','lineitem',10,'mypassword');
函数 rds_oss_fdw_load_data_execute 会等待数据导入的完成才返回。
期间,我们可以通过下列 SQL 查看正在工作的异步会话状态
select application_name, state, pid,query, now() - xact_start as xact from pg_stat_activity where state != 'idle' and application_name='oss_loader' order by xact desc;
同时,我们也可以随时中断数据导入工作
select pg_terminate_backend(pid),application_name, state ,query from pg_stat_activity where state != 'idle' and pid != pg_backend_pid() and application_name='oss_loader';
我们也很容易看到整个数据装载的进度(单位 MB)
select
(
select sum(size)/1024/1024 as complete from oss_fdw_load_status where status = 1
)a,
(
select sum(size)/1024/1024 as full from oss_fdw_load_status
)b;
使用 TPCC 100GB的数据进行装载测试,耗时 10 分钟,平均 170MB/S
select rds_oss_fdw_load_data_prepare('t_oss2','lineitem');
select rds_oss_fdw_load_data_execute('t_oss2','lineitem',10,'123456Zwj');
select sum(size)/1024/1024 from oss_fdw_load_status;
?column?
--------------------
22561.919849395752
(1 row)
select pg_size_pretty(pg_relation_size(oid)) from pg_class where relname = 'lineitem';
pg_size_pretty
----------------
101 GB
(1 row)
本文使用 plsql + dblink 的方式加速了 OSS 的数据导入。另外,大家也可以关注到以下三点