What is a transaction?


Transaction is an atomic unit of work on database. It's a sequence of actions (various SQL statements) that ends with either COMMIT, ROLLBACK or breaking of client's connection.

If you commit the transaction, all your changes become valid in the database and other users can see it under a few rules:

- those who have READ COMMITED transations, see it immediately
- those who have SNAPSHOT transactions, must start a new transaction
- those who had DIRTY READ transaction were able to see the changes as you made them (even before commiting)

If you rollback, all your changes are undone, except GENERATORS and EXTERNAL TABLES which are outside of transaction control.

If the connection breaks, transaction remains active until a new one comes and decides that the old one is invalid and rolls it back. Sometimes it can happen that some transaction's state is undetermined, and it's called a limbo transaction. This may happen with transactions that span multiple databases. You need to use the gfix tool either option -t for two phase recovery or -c and -r options to commit or rollback such transactions manually.

It is important that you keep your transactions as short as possible since bad transaction management is a cause for many performance problems: big database grow, slow queries, user lockups, etc.


Do you find this FAQ incorrect or incomplete? Please e-mail us what needs to be changed. To ensure quality, each change is checked by our editors (and often tested on live Firebird databases), before it enters the main FAQ database. If you desire so, the changes will be credited to your name. To learn more, visit our add content page.



All contents are copyright © 2007-2024 FirebirdFAQ.org unless otherwise stated in the text.


Links   Firebird   News   FlameRobin   Powered by FB: Home Inventory   Euchre  
Add content   About  

Categories
 Newbies
 SQL
 Installation and setup
 Backup and restore
 Performance
 Security
 Connectivity and API
 HOWTOs
 Errors and error codes
 Miscellaneous