I am using PostgreSQL 9.6.
I have a PROCEDURE in sql server. That makes use of a try catch block. It looks a little bit like the code below:
BEGIN TRANSACTION
BEGIN TRY
--do stuff here
COMMIT TRANSACTION
END TRY
BEGIN CATCH
ROLLBACK TRANSACTION
--do error stuff here
END CATCH
Upon doing some research, It seems like postgres does not make use of try catch. Is there some way to handle this in postgres the same way sql server does?
Callbacks can handle potential errors:
https://www.postgresql.org/docs/9.4/static/ecpg-errors.html
Related
I am using Postgres 13.5 and I am unsure how to combine commit and error handling in a stored procedure or DO block. I know that if I include the EXCEPTION clause in my block, then I cannot include a commit.
I am new to Postgres. It has also been over 15 years since I have written SQL that was working with transactions. When I was working with transactions I was using Oracle and recall using AUTONOMOUS_TRANSACTION to resolve some of these issues. I am just not sure how to do something like that in Postgres.
Here is a very simplified DO block. As I said above, I know that the Commits will cause the procedure to throw and exception. But, if I remove the EXCEPTION clause, then how will I trap an error if it happens? After reading many things, I still have not found a solution. So, I am not understanding something that will lead me to the solution.
Do
$$
DECLARE
v_Start timestamptz;
v_id integer;
v_message_type varchar(500);
Begin
select current_timestamp into start;
select q.id, q.message_type into (v_id, v_message_type) from message_queue;
call Load_data(v_id, v_message_type);
commit; -- if Load_Data completes successfully, I want to commmit the data
insert into log (id, message_type, Status, start, end)
values (v_id, v_message_type, 'Success', v_start, Currrent_Timestamp);
commit; -- commit the log issert for success
EXCEPTION
WHEN others THEN
insert into log (id, message_type, status, start, end, error_message)
values (v_id, v_message_type, 'Failue', v_start, Currrent_Timestamp, SQLERRM || '', ' ||
SQLSTATE );
commit; -- commit the log insert for failure.
end;
$$
Thanks!
Since this is a pattern that I will have to do tens of times, I want to understand the right way to do this.
Since you cannot use transaction management statements in a subtransaction, you will have to move part of the processing to the client side.
But your sample code doesn't need any transaction management at all! Simply remove all the COMMIT statements, and the procedure will work just as you want it to. Remember that PostgreSQL uses the autocommit mode, so your procedure call from the client will automatically run in its own transaction and commit when it is done.
But perhaps your sample code is simplified, and you would like more complicated processing (looping etc.) in your actual use cases. So let's discuss your options:
One option is to remove the EXCEPTION handler and move only that part to the client side: if the procedure causes an error, roll back and insert a log message. Another, perhaps cleaner, method is to move the whole transaction management to the client side. In that case, you would replace the complete procedure with client code and call load_data directly from client code.
I have an exception in Oracle PL/SQL that needs to be ported to PostgreSQL pl/pgsql. Below is the oracle variant
EXCEPTION
WHEN OTHERS THEN
NULL;
What is the PL/PGSQL variant?
It's the same syntax. Compare the 2 following executions:
DO
$$
BEGIN
RAISE division_by_zero;
EXCEPTION
WHEN OTHERS THEN
NULL;
END;
$$
DO
And:
DO
$$
BEGIN
RAISE division_by_zero;
END;
$$
ERROR: division_by_zero
CONTEXT: PL/pgSQL function inline_code_block line 3 at RAISE
DO NOT port this as it is. It is a BUG ALWAYS. If you do nothing else at least log the error. If where it occurs is interactive, or data loading, or report generating, or a whole host of others then create some kind of message indicating the process failed. If users are depending on this data and it is not there it is your application that is broken, not the users expectations. I understand your are migrating a system but while doing so you should not carry forward obvious bugs. This is one.
First, avoid trapping "any exception"s like that with no specific behavior at all. Except for very simple functions, consider logging it somewhere, or rewrite the code in a more elegant manner.
I found it here: apparently, you don't need to put anything at all.
You should try the following:
EXCEPTION
WHEN OTHERS THEN
-- Do nothing
Hope it helps.
Working on some basic tests, I discovered that I cannot ROLLBACK a transaction inside a PLPGSQL function for I get an error:
ERROR: cannot begin/end transactions in PL/pgSQL
HINT: Use a BEGIN block with an EXCEPTION clause instead.
So I instead do:
RAISE EXCEPTION "Test passed";
Does anyone have a better way?
Functions in PostgreSQL not allow commit or rollback operation inside , just can do it in procedure from versión 11.
https://www.postgresql.org/docs/11/plpgsql-transactions.html
Regards
When you raise a exception, then ROLLBACK to near safepoint is called automatically.
Against to other databases, is not necessary (possible) to handle transactions manually.
I am creating a Postgres function where I want to insert data into multiple tables and if any of them get failed then I want to rollback the transaction. But while writing the code begin transaction; in my function it says below error: ERROR: syntax error at or near "transaction"
PL/PgSQL functions cannot begin or commit transactions.
You appear to want autonomous transactions, but they are not supported.
Perhaps you can do what you need with a PL/PgSQL BEGIN ... EXCEPTION ... block. You can abort the (sub)transaction with a RAISE command to raise an error, instead of ROLLBACK.
What is the most elegant way to identify an error into transaction? At this time my code is like:
begin transaction tx1
update ....
insert ....
if ##error = 0
commit
else
rollback
end
This only catch last operation error, in this case errors on insert but not first operation error, in my case, update errors. How can I improve my code?
Have you looked at TRY/CATCH?
http://msdn.microsoft.com/en-us/library/ms175976.aspx
Of course you'll still only be able to catch the first error that sent you into CATCH if you do something like this:
BEGIN TRANSACTION; -- not sure why you're using a named transaction
BEGIN TRY
UPDATE ...
INSERT ...
COMMIT TRANSACTION;
END TRY
BEGIN CATCH
PRINT ERROR_MESSAGE();
ROLLBACK TRANSACTION;
END CATCH
But you can wrap each operation in its own TRY/CATCH, e.g.
BEGIN TRANSACTION; -- still not sure why you're using a named transaction
BEGIN TRY
UPDATE ...
COMMIT TRANSACTION;
END TRY
BEGIN CATCH
PRINT ERROR_MESSAGE();
ROLLBACK TRANSACTION;
END CATCH
BEGIN TRANSACTION;
BEGIN TRY
INSERT ...
COMMIT TRANSACTION;
END TRY
BEGIN CATCH
PRINT ERROR_MESSAGE();
ROLLBACK TRANSACTION;
END CATCH
But then I'm not sure what rules you'd want to follow here... do you want the insert to succeed if the update failed? If you want all actions to succeed or fail as a group then you want the first approach where everything is attempted in one TRY.
Also you should look at Erland Sommarskog's bible on error handling:
http://www.sommarskog.se/error_handling_2005.html