int DB_ENV->set_tx_max(DB_ENV *dbenv, u_int32_t tx_max);
Set the maximum number of active transactions that are supported by the environment. This value bounds the size of backing shared memory regions. Note that child transactions must be counted as active until their ultimate parent commits or aborts.
When there are more than the specified number of concurrent transactions, calls to DB_ENV->txn_begin will fail (until some active transactions complete). If no value is specified, a default value of 20 is used.
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 interface may not be called after the DB_ENV->open interface 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 database environment's maximum number of active transactions may also be set 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 may fail and return a non-zero error for the following conditions:
Called after DB_ENV->open was called.
The DB_ENV->set_tx_max method may fail and return a non-zero error for errors specified for other Berkeley DB and C library or system functions. If a catastrophic error has occurred, the DB_ENV->set_tx_max method may fail and return DB_RUNRECOVERY, in which case all subsequent Berkeley DB calls will fail in the same way.
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