Re: dblink ,dblink_exec not participating in a Transaction??

[carty mc <cartymc3@xxxxxxxxx>]

Jon,

Thanks for the reply.

As i explained earlier, I am using java (via hibernate) to control the overall transaction.

I cannot have begin/rollback statements for dblink_exec. 

Only when the entire method call from java succeeds I want the transaction to be commited.

 

I dont want a funtion controlling the transaction partially. I thought there would be easier way for letting dblink participate in the incoming transaction (i.e. from java-jdbc method call) and commit only when the main transaction commits.

I wanted to treat the whole updates inside the function as one, and let java method call decide whether to commit or rollback.

 

thanks,

 

 

"Roberts, Jon" <Jon.Roberts@xxxxxxxxxxx> wrote:

I sent this just a few days ago to the list on a similar question.  You will need to move your code from the trigger to a regular function like the one below.  The function should handle the update to the table and also to the linked database. 

 

create table log (update_datetime timestamp);

 

create or replace function fn_test (p_fail boolean) returns void as $$ declare

    v_sql varchar;

    v_int int;

 

begin

    perform dblink_connect('pg', 'dbname=postgres user=scott password=tiger host=localhost');   

 

    v_sql := 'begin;';

    perform dblink_exec('pg', v_sql, false);

 

    v_sql := 'insert into log values (now())';

    perform dblink_exec('pg', v_sql, false);

 

    if p_fail then

      v_int := 1/0;

    end if;

   

    v_sql := 'commit;';

    perform dblink_exec('pg', v_sql, false);

 

    perform dblink_disconnect('pg');

exception

  when others then

      v_sql := 'rollback;';

      perform dblink_exec('pg', v_sql, false);

      perform dblink_disconnect('pg');

      raise exception '%', sqlerrm;

end;

$$

language 'plpgsql';

 

 

Now that is a basic function that will insert data into the postgres database via a dblink.  If you pass in fail, it will hit "division by zero" and rollback both the linked transaction and the primary transaction of the function. 

 

select fn_test(false);

select * from log;

--you see a new row

 

select fn_test(true)

--ERROR:  division by zero

select * from log;

--you see that a new row wasn't inserted.

 

 

 

Jon

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From: pgsql-general-owner@xxxxxxxxxxxxxx [mailto:pgsql-general-owner@xxxxxxxxxxxxxx] On Behalf Of carty mc
Sent: Tuesday, April 01, 2008 6:56 PM
To: pgsql-general@xxxxxxxxxxxxxx
Subject: Re: dblink ,dblink_exec not participating in a Transaction??

 

Just to clarify few things in the above posting.

My Main DB Client is java (using hibernate) which has Main Transaction Manager.

This one controls the overall transaction

Work flow is as follows:

1)java program updates a table in Database A

2) As a result Trigger procedure defined for this table gets executed which inturn uses dblink_exec program to update a table in Different database B.

3) Control goes back to java program.

java program will rollback the whole transaction if any errors/exceptions are found.

or else java program will issue a commit.

Java program will determine whether to commit or rollback. It is the main transaction manager.

 

In this case the updates that were made using dblink_exec are not getting rolled back in Database B.

 

 

 

carty mc <cartymc3@xxxxxxxxx> wrote:

How I can make dblink to participate in transaction so that remote changes made by dblink can only be committed if only local transaction succeds.

 

Here is my current scenario:

 

I am using two databases A & B.  In Database A, I have trigger procedure written for  a Table . In this trigger procedure, I use dblink_exec  to update a table in the other database B.

The problem I am having right now is my trigger procedure currently participates in a transaction.  If Transaction rollsback: whatever trigger procedure modified in database A is getting rolled back whereas Chages made to a table in Database B using dblink_exec are not.

Note: Transaction can be rolled back due to excpetions any where from main db client which updates a table in database A .

 

So my question is there a way to  tell dblink_exec to participate in a Transaction. This way commits wont go to table in database B until transaction completed succesfully.

 

 

I appreciate any help,

 

thanks,

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