I am using three insert statements, and if there is an error in the third statement, I want to rollback the first and the second one. If there is no way to do this, please tell me a different approach to handle this in PostgresqQL.
If I use COMMIT or ROLLBACK, I get an error.
CREATE OR REPLACE FUNCTION TEST1 ()
RETURNS VOID
LANGUAGE 'plpgsql'
AS $$
BEGIN
INSERT INTO table1 VALUES (1);
INSERT INTO table1 VALUES (2);
INSERT INTO table1 VALUES ('A');
COMMIT;
EXCEPTION
WHEN OTHERS THEN
ROLLBACK;
END;$$;
The above code is not working; COMMIT and ROLLBACK are not supported by PostgreSQL functions.
You cannot use transaction statements like SAVEPOINT, COMMIT or ROLLBACK in a function. The documentation says:
In procedures invoked by the CALL command as well as in anonymous code blocks (DO command), it is possible to end transactions using the commands COMMIT and ROLLBACK.
Ex negativo, since functions are not procedures that are invoked with CALL, you cannot do that in functions.
The BEGIN that starts a block in PL/pgSQL is different from the SQL statement BEGIN that starts a transaction.
Just remove the COMMIT from your function, and you have the solution: since the whole function is always run inside a single transaction, any error in the third statement will lead to a ROLLBACK that also undoes the first two statements.
Compared to other SQL languages, you should think that Postgres always takes care of the commit/rollback in case of error implicitly when you are inside a transaction.
Here is what the doc is saying:
Transactions are a fundamental concept of all database systems. The essential point of a transaction is that it bundles multiple steps into a single, all-or-nothing operation. The intermediate states between the steps are not visible to other concurrent transactions, and if some failure occurs that prevents the transaction from completing, then none of the steps affect the database at all.
CREATE OR REPLACE FUNCTION TEST1 ()
RETURNS VOID
LANGUAGE 'plpgsql'
AS $$
BEGIN
INSERT INTO table1 VALUES (1);
INSERT INTO table1 VALUES (2);
INSERT INTO table1 VALUES ('A');
COMMIT;
EXCEPTION
WHEN OTHERS THEN
ROLLBACK;
END;$$;
For transaction control we use PROCEDURE (From postgresql11) instead of FUCTION.
FUNCTION does not support transaction inside the function. This is the main difference between FUNCTION and PROCEDURE in PostgreSQL.
Your code should be:
CREATE OR REPLACE PROCEDURE TEST1 ()
RETURNS VOID
LANGUAGE 'plpgsql'
AS $$
BEGIN
INSERT INTO table1 VALUES (1);
INSERT INTO table1 VALUES (2);
INSERT INTO table1 VALUES ('A');
COMMIT;
EXCEPTION
WHEN OTHERS THEN
ROLLBACK;
END;$$;
Related
I'm new to Postgres, but with experience from Oracle. Trying to create a stored procedure which is going to:
Insert a row
Handle exceptions and in case of an exception insert a row into a log table by calling dedicated procedure
Emit an audit log record into a log table in case the whole procedure ran successfully
By pseudo code:
CREATE OR REPLACE PROCEDURE test.p_insert(IN p_test_param character varying)
LANGUAGE 'plpgsql'
SECURITY DEFINER
AS $BODY$
DECLARE
-- some declarations
BEGIN
BEGIN
INSERT INTO test.a(a) VALUES (p_test_param);
EXCEPTION
WHEN OTHERS THEN
-- GET STACKED DIAGNOSTICS
CALL test.p_insert_log(...); -- Inserts a row into a log table, another COMMIT may be required?
RAISE;
END;
COMMIT; -- CAN'T DO
BEGIN
IF (SELECT test.f_debug()) THEN
CALL test.p_insert_log(...); -- Audit the execution
END IF;
END;
COMMIT; -- CAN'T DO EITHER
END;
$$BODY$$;
However when I try to test the procedure out from an anonymous block in PgAdmin such as:
BEGIN;
DO
LANGUAGE plpgsql
$$
BEGIN
CALL test.p_insert(
p_test_param => 'test'
);
END;
$$
I'm getting an error ERROR: invalid transaction termination. How can I get rid of it? My objective is to let the procedure carry out the transaction control, I don't want the caller to COMMIT or ROLLBACK anything. If I remove both COMMIT commands from the code of the procedure, it executes well, however the invoker must explicitly COMMIT or REVOKE the transaction afterwards, which is not desired. In Oracle the pseudo code with COMMIT statements would work, in Postgres it doesn't seem to work as I would like to. Could you please help me out? Thanks
Your code will work as intended. Perhaps you made some mistake in calling the code:
you cannot call the procedure from a function
you cannot call the procedure in an explicitly started transaction:
BEGIN;
CALL p_insert('something); -- will fail
COMMIT;
I have many stored procedure in my postgresql db,
and for some reason i need to run many procedure in transaction so if there is a error it will rollback.
is there any way to do this?
edit 1
i run this through java and for some reason i cant make transaction from java and i cant run query string, just store procedure only.
I actually thinking making procedure like this
CREATE OR REPLACE FUNCTION ldt_pricing_rule_v1_api.start()
RETURNS VOID
LANGUAGE PLPGSQL
SECURITY DEFINER
AS $$
BEGIN
EXECUTE 'begin transaction'
RETURN;
END
$$;
select ldt_pricing_rule_v1_api.start();
but it's will display this
ERROR: cannot begin/end transactions in PL/pgSQL
HINT: Use a BEGIN block with an EXCEPTION clause instead.
BEGIN ... COMMIT should to work.
BEGIN
SELECT func1();
SELECT func2();
COMMIT;
PostgreSQL 11 (it is not released yet) has procedures where you can control transactions explicitly. Procedures are started by CALL statement like any other databases. Now, PostgreSQL functions doesn't allow control transactions (explicitly).
Any PostgreSQL function is executed under transaction - explicitly started by user (like my example), or implicitly started by system (by autocommit mode).
So outer BEGIN starts explicit transaction:
BEGIN
SELECT func1();
SELECT func2();
COMMIT;
and if there is any unhandled fail, then only ROLLBACK command is available.
or implicit transaction:
CREATE OR REPLACE FUNCTION outerfx()
RETURNS void AS $$
BEGIN
PERFORM func1();
PERFORM func2();
END;
$$ LANGUAGE plpgsql;
SELECT outerfx(); -- starts outer transaction implicitly.
Now, functions func1, func2 are executed under transaction too.
I have the following stored procedure
CREATE OR REPLACE FUNCTION testFunction(iRowID1 integer, iRowID2 integer) RETURNS void AS $$
BEGIN
UPDATE Table1 SET Value1=Value1+1 WHERE rowID=iRowID1;
UPDATE Table1 SET Value1=Value1-1 WHERE rowID=iRowID2;
END;
$$ LANGUAGE plpgsql;
If I run the following two commands concurrently
SELECT testFunction(1,2);
SELECT testFunction(2,1);
I get a deadlock detected error for one of the commands. Is there some way to avoid this deadlock?
I can't test this right now as I don't have access to a PostgreSQL database at the moment, but in theory it should work, as deadlocks can always be avoided if you lock things in the same order and never escalate a lock level (upgrade a read lock to a write lock, for example).
Do the updates in a specific order:
CREATE OR REPLACE FUNCTION testFunction(iRowID1 integer, iRowID2 integer) RETURNS void AS $$
BEGIN
IF iRowID1 < iRowID2 THEN
UPDATE Table1 SET Value1=Value1+1 WHERE rowID=iRowID1;
UPDATE Table1 SET Value1=Value1-1 WHERE rowID=iRowID2;
ELSE
UPDATE Table1 SET Value1=Value1-1 WHERE rowID=iRowID2;
UPDATE Table1 SET Value1=Value1+1 WHERE rowID=iRowID1;
END IF
END;
$$ LANGUAGE plpgsql;
That will always update the rows in numerically-ascending order, thus in your example row 1 will always be updated before row 2, and the second invocation can't start its update until the first invocation is done.
I am seeking clarification of how to ensure an atomic transaction in a plpgsql function, and where the isolation level is set for this particular change to the database.
In the plpgsql function shown below, I want to make sure that BOTH the deletion AND the insertion succeed. I am getting an error when I try to wrap them in a single transaction:
ERROR: cannot begin/end transactions in PL/pgSQL
What happens during execution of the function below if another user has added a default behavior for circumstances ('RAIN', 'NIGHT', '45MPH') after this function has deleted the custom row but before it has had a chance to insert the custom row? Is there an implicit transaction wrapping the insert and delete so that both are rolled back if another user has changed either of the rows referenced by this function? Can I set the isolation level for this function?
create function foo(v_weather varchar(10), v_timeofday varchar(10), v_speed varchar(10),
v_behavior varchar(10))
returns setof CUSTOMBEHAVIOR
as $body$
begin
-- run-time error if either of these lines is un-commented
-- start transaction ISOLATION LEVEL READ COMMITTED;
-- or, alternatively, set transaction ISOLATION LEVEL READ COMMITTED;
delete from CUSTOMBEHAVIOR
where weather = 'RAIN' and timeofday = 'NIGHT' and speed= '45MPH' ;
-- if there is no default behavior insert a custom behavior
if not exists
(select id from DEFAULTBEHAVIOR where a = 'RAIN' and b = 'NIGHT' and c= '45MPH') then
insert into CUSTOMBEHAVIOR
(weather, timeofday, speed, behavior)
values
(v_weather, v_timeofday, v_speed, v_behavior);
end if;
return QUERY
select * from CUSTOMBEHAVIOR where ... ;
-- commit;
end
$body$ LANGUAGE plpgsql;
A plpgsql function automatically runs inside a transaction. It all succeeds or it all fails. The manual:
Functions and trigger procedures are always executed within a
transaction established by an outer query — they cannot start or
commit that transaction, since there would be no context for them to
execute in. However, a block containing an EXCEPTION clause
effectively forms a subtransaction that can be rolled back without
affecting the outer transaction. For more about that see Section 42.6.6.
So, if you need to, you can catch an exception that theoretically might occur (but is very unlikely).
Details on trapping errors in the manual.
Your function reviewed and simplified:
CREATE FUNCTION foo(v_weather text
, v_timeofday text
, v_speed text
, v_behavior text)
RETURNS SETOF custombehavior
LANGUAGE plpgsql AS
$func$
BEGIN
DELETE FROM custombehavior
WHERE weather = 'RAIN'
AND timeofday = 'NIGHT'
AND speed = '45MPH';
INSERT INTO custombehavior (weather, timeofday, speed, behavior)
SELECT v_weather, v_timeofday, v_speed, v_behavior
WHERE NOT EXISTS (
SELECT FROM defaultbehavior
WHERE a = 'RAIN'
AND b = 'NIGHT'
AND c = '45MPH'
);
RETURN QUERY
SELECT * FROM custombehavior WHERE ... ;
END
$func$;
If you actually need to begin/end transactions like indicated in the title look to SQL procedures in Postgres 11 or later (CREATE PROCEDURE). See:
In PostgreSQL, what is the difference between a “Stored Procedure” and other types of functions?
Update: after PostgreSQL version 11. you can control transaction inside Store Procedure.
=====
Before Version 10:
START TRANSACTION;
select foo() ;
COMMIT;
"Unfortunately Postgres has no stored procedures, so you always need to manage the transaction in the calling code" – a_horse_with_no_name
Transaction in an exception block - how?
Is a PostgreSQL function such as the following automatically transactional?
CREATE OR REPLACE FUNCTION refresh_materialized_view(name)
RETURNS integer AS
$BODY$
DECLARE
_table_name ALIAS FOR $1;
_entry materialized_views%ROWTYPE;
_result INT;
BEGIN
EXECUTE 'TRUNCATE TABLE ' || _table_name;
UPDATE materialized_views
SET last_refresh = CURRENT_TIMESTAMP
WHERE table_name = _table_name;
RETURN 1;
END
$BODY$
LANGUAGE plpgsql VOLATILE SECURITY DEFINER;
In other words, if an error occurs during the execution of the function, will any changes be rolled back? If this isn't the default behavior, how can I make the function transactional?
PostgreSQL 12 update: there is limited support for top-level PROCEDUREs that can do transaction control. You still cannot manage transactions in regular SQL-callable functions, so the below remains true except when using the new top-level procedures.
Functions are part of the transaction they're called from. Their effects are rolled back if the transaction rolls back. Their work commits if the transaction commits. Any BEGIN ... EXCEPT blocks within the function operate like (and under the hood use) savepoints like the SAVEPOINT and ROLLBACK TO SAVEPOINT SQL statements.
The function either succeeds in its entirety or fails in its entirety, barring BEGIN ... EXCEPT error handling. If an error is raised within the function and not handled, the transaction calling the function is aborted. Aborted transactions cannot commit, and if they try to commit the COMMIT is treated as ROLLBACK, same as for any other transaction in error. Observe:
regress=# BEGIN;
BEGIN
regress=# SELECT 1/0;
ERROR: division by zero
regress=# COMMIT;
ROLLBACK
See how the transaction, which is in the error state due to the zero division, rolls back on COMMIT?
If you call a function without an explicit surounding transaction the rules are exactly the same as for any other Pg statement:
BEGIN;
SELECT refresh_materialized_view(name);
COMMIT;
(where COMMIT will fail if the SELECT raised an error).
PostgreSQL does not (yet) support autonomous transactions in functions, where the procedure/function could commit/rollback independently of the calling transaction. This can be simulated using a new session via dblink.
BUT, things that aren't transactional or are imperfectly transactional exist in PostgreSQL. If it has non-transactional behaviour in a normal BEGIN; do stuff; COMMIT; block, it has non-transactional behaviour in a function too. For example, nextval and setval, TRUNCATE, etc.
As my knowledge of PostgreSQL is less deeper than Craig Ringer´s I will try to give a shorter answer: Yes.
If you execute a function that has an error in it, none of the steps will impact in the database.
Also, if you execute a query in PgAdmin the same happen.
For example, if you execute in a query:
update your_table yt set column1 = 10 where yt.id=20;
select anything_that_do_not_exists;
The update in the row, id = 20 of your_table will not be saved in the database.
UPDATE Sep - 2018
To clarify the concept I have made a little example with non-transactional function nextval.
First, let´s create a sequence:
create sequence test_sequence start 100;
Then, let´s execute:
update your_table yt set column1 = 10 where yt.id=20;
select nextval('test_sequence');
select anything_that_do_not_exists;
Now, if we open another query and execute
select nextval('test_sequence');
We will get 101 because the first value (100) was used in the latter query (that is because the sequences are not transactional) although the update was not committed.
https://www.postgresql.org/docs/current/static/plpgsql-structure.html
It is important not to confuse the use of BEGIN/END for grouping statements in PL/pgSQL with the similarly-named SQL commands for transaction control. PL/pgSQL's BEGIN/END are only for grouping; they do not start or end a transaction. Functions and trigger procedures are always executed within a transaction established by an outer query — they cannot start or commit that transaction, since there would be no context for them to execute in. However, a block containing an EXCEPTION clause effectively forms a subtransaction that can be rolled back without affecting the outer transaction. For more about that see Section 39.6.6.
In the function level, it is not transnational. In other words, each statement in the function belongs to a single transaction, which is the default db auto commit value. Auto commit is true by default. But anyway, you have to call the function using
select schemaName.functionName()
The above statement 'select schemaName.functionName()' is a single transaction, let's name the transaction T1, and so the all the statements in the function belong to the transaction T1. In this way, the function is in a single transaction.
Postgres 14 update: All statements written in between the BEGIN and END block of a Procedure/Function is executed in a single transaction. Thus, any errors arising while execution of this block will cause automatic roll back of the transaction.
Additionally, the ATOMIC Transaction including triggers as well.