#include <db.h>

int
DB_ENV->set_tx_max(DB_ENV *dbenv, u_int32_t max);

int
DB_ENV->get_tx_max(DB_ENV *dbenv, u_int32_t *tx_maxp);

Configure the Berkeley DB database environment to support at least max active transactions. This value bounds the size of the memory allocated for transactions. Child transactions are counted as active until they either commit or abort.

Transactions that update multiversion databases are not freed until the last page version that the transaction created is flushed from cache. This means that applications using multi-version concurrency control may need a transaction for each page in cache, in the extreme case.

When all of the memory available in the database environment for transactions is in use, calls to DB_ENV->txn_begin will fail (until some active transactions complete). If this interface is never called, the database environment is configured to support at least 100 active transactions.

The database environment's number of active transactions may also be configured using the environment's DB_CONFIG file. The syntax of the entry in that file is a single line with the string "set_tx_max", one or more whitespace characters, and the number of transactions. Because the DB_CONFIG file is read when the database environment is opened, it will silently overrule configuration done before that time.

The DB_ENV->set_tx_max method configures a database environment, not only operations performed using the specified DB_ENV handle.

The DB_ENV->set_tx_max method may not be called after the DB_ENV->open method is called. If the database environment already exists when DB_ENV->open is called, the information specified to DB_ENV->set_tx_max will be ignored.

The DB_ENV->set_tx_max method returns a non-zero error value on failure and 0 on success.

• The max parameter configures the minimum number of simultaneously active transactions supported by Berkeley DB database environment.

The DB_ENV->set_tx_max method may fail and return one of the following non-zero errors:

• If the method was called after DB_ENV->open was called; or if an invalid flag value or parameter was specified.

The DB_ENV->get_tx_max method returns the number of active transactions.

The DB_ENV->get_tx_max method may be called at any time during the life of the application.

The DB_ENV->get_tx_max method returns a non-zero error value on failure and 0 on success.

• The DB_ENV->get_tx_max method returns the number of active transactions in tx_maxp.