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Berkeley DB Reference Guide:
  Transaction Subsystem

# Configuring transactions

There is only a single parameter used in configuring transactions, the DB_TXN_NOSYNC flag. Setting the DB_TXN_NOSYNC flag to DBENV->open when opening a transaction region changes the behavior of transactions not to synchronously flush the log during transaction commit.

This change will significantly increase application transactional throughput. However, it means that while 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.

The application may also limit the number of simultaneous outstanding transactions supported by the environment by calling the DBENV->set_tx_max function. When this number is met, additional calls to txn_begin will fail until some active transactions complete.

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