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Berkeley DB Reference Guide:
  Transaction Subsystem

### Configuring transactions

The application may change the number of simultaneous outstanding transactions supported by the Berkeley DB environment by calling the DB_ENV->set_tx_max method. This will also set the size of the underlying transaction subsystem's region. When the number of outstanding transactions is reached, additional calls to DB_ENV->txn_begin will fail until some active transactions complete.

There is an additional parameter used in configuring transactions; the DB_TXN_NOSYNC flag. Setting the DB_TXN_NOSYNC flag to DB_ENV->set_flags when opening a transaction region changes the behavior of transactions to not write or synchronously flush the log during transaction commit.

This change may significantly increase application transactional throughput. However, it means that although transactions will continue to exhibit the ACI (atomicity, consistency, and isolation) properties, they will not have D (durability). Database integrity will be maintained, but it is possible that some number of the most recently committed transactions may be undone during recovery instead of being redone.

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