当一台服务器不可用时如何克服dblink问题

Posted 2021-04-16

我创建这样的视图

 CREATE view  zaliha as
    SELECT * FROM public.dblink
('meteor','SELECT z.skladiste,ar.sifra,z.velicina,z.kolicina,z.rezervacija,z.kolicina - z.rezervacija
 as raspolozivo
 from zaliha z, artikli ar
 where ar.id=z.artikal
 and (kolicina <> 0 or kolicina <> 0)') 
AS DATA(skladiste CHARACTER VARYING, sifra CHARACTER VARYING, velicina CHARACTER VARYING, kolicina NUMERIC,
        rezervacija NUMERIC, raspolozivo NUMERIC)

        union

SELECT * FROM public.dblink
('dorcol','SELECT z.skladiste,ar.sifra,z.velicina,z.kolicina,z.rezervacija,z.kolicina - z.rezervacija
 as raspolozivo
 from zaliha z, artikli ar
 where ar.id=z.artikal
 and (kolicina <> 0 or kolicina <> 0)') 
AS DATA(skladiste CHARACTER VARYING, sifra CHARACTER VARYING, velicina CHARACTER VARYING, kolicina NUMERIC,
        rezervacija NUMERIC, raspolozivo NUMERIC)

        union

SELECT * FROM public.dblink
('uzice','SELECT z.skladiste,ar.sifra,z.velicina,z.kolicina,z.rezervacija,z.kolicina - z.rezervacija
 as raspolozivo
 from zaliha z, artikli ar
 where ar.id=z.artikal
 and (kolicina <> 0 or kolicina <> 0)') 
AS DATA(skladiste CHARACTER VARYING, sifra CHARACTER VARYING, velicina CHARACTER VARYING, kolicina NUMERIC,
        rezervacija NUMERIC, raspolozivo NUMERIC)

实际上这是3个相同选择的联合，但来自不同的服务器。我需要的是获得所有可用服务器的结果，如果1台服务器出现错误，则排除该结果。例如，服务器流星和dorcol可用，而服务器uzice则不可用，我只想查看流星和dorcol的此视图结果，并排除uzice的错误。

当一台服务器不可用时出现错误：

ERROR:  could not establish connection

    DETAIL:  could not connect to server: Connection timed out
        Is the server running on host "x.x.x.x" and accepting
        TCP/IP connections on port 5432?

有可能吗？

答案

您无法使用视图执行此操作，但是可以使用设置的返回函数来执行此操作。

为了简单起见，我已将其更改为使用pgbench_branches表。

CREATE OR REPLACE FUNCTION public.fail_tolerant()                                                                                                        
 RETURNS SETOF pgbench_branches
 LANGUAGE plpgsql
AS $function$ 
declare 
connections text[]='{host=127.0.0.1,host=192.168.0.bad}';
conn text;  
begin 
  foreach conn in array connections loop 
    begin
      return query SELECT * FROM public.dblink (conn,'SELECT * from pgbench_branches') AS DATA(bid integer, bbalance integer, filler character(88));
    EXCEPTION when others then          
       RAISE NOTICE 'exception caught';
    END;
  end loop;
end $function$;

这不具有UNION的重复数据删除功能，因此您需要单独添加：

select distinct * from fail_tolerant();

您可能想要比我在这里做的更好的日志记录。如果有任何连接尝试被拒绝，而不是立即被接受或拒绝，则可能需要很长时间才能完成。因此，您可能需要在每个连接字符串中设置一个connect_timeout。