Re: How to Force Transactions to Process Serially on A Table

O Lane Van Ingen έγραψε στις Dec 19, 2005 :

> I am using PL/SQL functions on Windows 2003, version 8.0.1.
> 
> I have not used explicit PostgreSQL LOCKing before, but I need some advice
> on how properly to use some explicit locking. I think that duplicate key
> violations I am now getting are the result.
> 
> I want to force transactions being used to update a table to be processed on
> a first-come, first-served basis. I want my Pl/sql function to execute to
> completion on each transaction before another starts.
> 
> Need some advice on how to do this. From what I can read in the docs, it
> looks like I need to solve the problem by using the following, but doing so
> gives me an SPI_execution error:
>   BEGIN;
>   LOCK <table> IN SHARE ROW  EXCLUSIVE MODE;
>     lock adns_report_hour_history in share row exclusive mode;
>   INSERT INTO <table> VALUES ...  - or - UPDATE <table> SET ....
>   COMMIT;
> Will this make the next transaction wait until the previous transaction has
> completed? Do I need to set any config parameters?
> 
> If you can include an actual code snippet in the response, it would help ...

what you want is to set the xaction isolation level.

BEGIN;
SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;
......
COMMIT;

Be prepared for serialization failures though.

> 
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-- 
-Achilleus