Berkeley-DB: Atomic transactions over multiple databases

Question

I want to use different Berkeley-DB databases to store different classes of objects in my application. Transactions in a single DB can be done atomically using DbTxn::commit. However, if I'm using multiple databases, I have to create multiple transactions (one for each database), right? In this case, if committing the first succeeds but the second fails, is there a way to roll back the already committed first transaction? (As far as I understand DbTxn::abort, this is no longer possible to use after the transaction has been committed.)

Is there some way to achieve atomic transactions across multiple databases?

Answer 1

If you are using multiple databases then you DON'T have to create multiple transactions. By using a single transaction, you can operate on multiple DBs.

Please see this link for the documentation of Db::Open().

It has the 'DbTxn *txnid' parameter. You can specify a transaction id returned by the DB_ENV->txn_begin() API. So before opening a DB, a transaction id should be obtained.

Carefully read the note under the parameter 'txnid' in the given documentation link.

Please note that, you should Not specify DB_AUTO_COMMIT the flag in the Db::open() API. Instead of that, you will specify the same transaction id for the parameter 'txnid' for all DBs that you want to operate on. In this way you can achieve atomic transactions across multiple databases.

Answer 2

In general, you need something like distributed tranzaction manager, the full answer fills books. See "The Berkeley DB Book", CHAPTER 9, "Distributed Transactions and Data-Distribution Strategies", ISBN-10: 1-59059-672-2