Re: [SQL] Database consistency after a power shortage
Samuel Gendler wrote: On Wed, Dec 15, 2010 at 11:38 PM, Scott Marlowe scott.marl...@gmail.com mailto:scott.marl...@gmail.com wrote: On Wed, Dec 15, 2010 at 8:12 AM, Alberto blob2...@gmail.com mailto:blob2...@gmail.com wrote: Is there any way to make the 3 operations be one transaction for the database, so that it keeps them all consistent in case a power shortage occurs in the middle? Yes, put them in a transaction. begin; insert into head_invoice ... insert into detail_invocie ... insert into payments_x_header_invoice ... commit; Then they either all go or none go. But if the database transaction concept is new to you, I highly recommend you do a little reading about database transactions in general and postgres' implementation specifics as well. It can be very easy for you to make mistakes that can cause the database to get slow or use up a lot of disk if you use transactions without understanding at least a little of what is happening in the database while the transaction is open but uncommitted. Incidentally, any error on a query within the transaction will cause the transaction to automatically 'rollback' when the transaction completes, undoing all of the changes, or you can manually cancel a transaction by issuing a 'rollback;' statement instead of 'commit;' at the end. You can also (or more appropriately, in addition) equip your system with an uninterruptable power supply with enough capacity to coast over the power shortage interval, or to perform a controlled shutdown. I do not know how long it takes to do such a shutdown with postgreSQL, but it could involve stopping all new transactions from entering the system, and allowing those in process to complete. A UPS to allow 10 minutes of run-time is not normally considered too expensive. Mine will run for about an hour with new batteries, but after a few years it dwindles to about 1/2 hour. Then I get new ones. -- .~. Jean-David Beyer Registered Linux User 85642. /V\ PGP-Key: 9A2FC99A Registered Machine 241939. /( )\ Shrewsbury, New Jerseyhttp://counter.li.org ^^-^^ 09:30:01 up 14 days, 23:16, 4 users, load average: 5.61, 4.98, 4.89 -- Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-sql
Re: [SQL] Database consistency after a power shortage
On Wed, Dec 15, 2010 at 8:12 AM, Alberto blob2...@gmail.com wrote: My question is regarding a potential situation: I have a program that inserts values on 3 tables linked to each other. My program is used in a POS. In this specific case, the program has to update the tables header_invoice, detail_invoice and payments_x_header_invoice. In a normal operation, the program should insert first a registry on header_invoice, then insert N registries on detail_invoice referencing the header_invoice number. After that it should insert N registries regarding the payments related to the header_invoice, referencing again the invoice. So the order goes like this: 1) Insert 1 new registry on header_invoice 2) Insert N registries on detail_invoice referencing header_invoice 3) Insert N registries on payments_x_header_invoice referencing the header_invoice If lets say the header_invoice registry was inserted, operation was committed and then a power shortage occurs and the system shuts down. In that case the database will never know that more registries had to be inserted, because that happened on the application level. Is there any way to make the 3 operations be one transaction for the database, so that it keeps them all consistent in case a power shortage occurs in the middle? Yes, put them in a transaction. begin; insert into head_invoice ... insert into detail_invocie ... insert into payments_x_header_invoice ... commit; Then they either all go or none go. -- Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-sql
Re: [SQL] Database consistency after a power shortage
On Wed, Dec 15, 2010 at 11:38 PM, Scott Marlowe scott.marl...@gmail.comwrote: On Wed, Dec 15, 2010 at 8:12 AM, Alberto blob2...@gmail.com wrote: Is there any way to make the 3 operations be one transaction for the database, so that it keeps them all consistent in case a power shortage occurs in the middle? Yes, put them in a transaction. begin; insert into head_invoice ... insert into detail_invocie ... insert into payments_x_header_invoice ... commit; Then they either all go or none go. But if the database transaction concept is new to you, I highly recommend you do a little reading about database transactions in general and postgres' implementation specifics as well. It can be very easy for you to make mistakes that can cause the database to get slow or use up a lot of disk if you use transactions without understanding at least a little of what is happening in the database while the transaction is open but uncommitted. Incidentally, any error on a query within the transaction will cause the transaction to automatically 'rollback' when the transaction completes, undoing all of the changes, or you can manually cancel a transaction by issuing a 'rollback;' statement instead of 'commit;' at the end.
