3 ms·

How is it atomic? this goes for all 5 of the replies (one of you did not downvote discussion, I'm guessing that person is the only one not from the US). How doe

by bullen 10y ago

How is it atomic? this goes for all 5 of the replies (one of you did not downvote discussion, I'm guessing that person is the only one not from the US). How does mysql unwrite the deposit? There are always "parts" to everything. Two phase commit does not solve anything unless you have "undo the thing I did before the power was lost". Please refer to source code to prove your argumentation.

smallnamespace 10y ago
> How does mysql unwrite the deposit? Yes, the database either reverses the changes. https://en.wikipedia.org/wiki/Transaction_log https://en.wikipedia.org/wiki/Transaction_log If, after a start, the database is found in an inconsistent state or not been shut down properly, the database management system reviews the database logs for uncommitted transactions and rolls back the changes made by these transactions. Additionally, all transactions that are already committed but whose changes were not yet materialized in the database are re-applied. Both are done to ensure atomicity and durability of transactions.
matthewmacleod 10y ago
Please refer to source code to prove your argumentation. I'm not digging through source code for you; transactional atomicity is a well-known and thoroughly researched problem. Transactions in an ACID system are atomic by definition. They're designed in such a way that either an entire transaction occurs, or no part of a transaction occurs – in other words, it's not possible to partially apply a transaction, by design. There are a bunch of different approaches to implementing this. I'd guess that MySQL does something like write the complete set of modifications in a transaction to disk as a separate buffer, and only once the entire transaction is complete updating some associated metadata to add the transaction to the database. A power failure at any point will result in an uncommitted transaction, which will have no effect on the database. Here's the appropriate Wikipedia article for further reading -https://en.wikipedia.org/wiki/Atomicity_(database_systems) https://en.wikipedia.org/wiki/Atomicity_(database_systems) - lets suffice to say that if you are rejecting the idea that atomicity exists then I don't know what else to tell you. It's a core concept in information systems.
- bullen 10y ago
  I don't think so; if a MySQL transaction has two separate tables, at some point it has to write one and then the other remembering to remove the first if the second fails with power outage for example. I'm not rejecting anything, all I'm asking is; where is the code and how does it work? If you don't know then how come you are so confident it does work? I'm pretty sure the "write some status to a file and rollback if transaction incomplete on startup" code is pretty horrible on all SQL systems. And on top of that it doesn't scale. Defending status quo is always worth questioning.

by bullen 10y ago

smallnamespace 10y ago

> How does mysql unwrite the deposit? Yes, the database either reverses the changes. https://en.wikipedia.org/wiki/Transaction_log https://en.wikipedia.org/wiki/Transaction_log If, after a start, the database is found in an inconsistent state or not been shut down properly, the database management system reviews the database logs for uncommitted transactions and rolls back the changes made by these transactions. Additionally, all transactions that are already committed but whose changes were not yet materialized in the database are re-applied. Both are done to ensure atomicity and durability of transactions.

matthewmacleod 10y ago

Please refer to source code to prove your argumentation. I'm not digging through source code for you; transactional atomicity is a well-known and thoroughly researched problem. Transactions in an ACID system are atomic by definition. They're designed in such a way that either an entire transaction occurs, or no part of a transaction occurs – in other words, it's not possible to partially apply a transaction, by design. There are a bunch of different approaches to implementing this. I'd guess that MySQL does something like write the complete set of modifications in a transaction to disk as a separate buffer, and only once the entire transaction is complete updating some associated metadata to add the transaction to the database. A power failure at any point will result in an uncommitted transaction, which will have no effect on the database. Here's the appropriate Wikipedia article for further reading -https://en.wikipedia.org/wiki/Atomicity_(database_systems) https://en.wikipedia.org/wiki/Atomicity_(database_systems) - lets suffice to say that if you are rejecting the idea that atomicity exists then I don't know what else to tell you. It's a core concept in information systems.

bullen 10y ago
I don't think so; if a MySQL transaction has two separate tables, at some point it has to write one and then the other remembering to remove the first if the second fails with power outage for example. I'm not rejecting anything, all I'm asking is; where is the code and how does it work? If you don't know then how come you are so confident it does work? I'm pretty sure the "write some status to a file and rollback if transaction incomplete on startup" code is pretty horrible on all SQL systems. And on top of that it doesn't scale. Defending status quo is always worth questioning.