DbEnv::set_tx_max()
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## DbEnv::set_tx_max()

    #include <db_cxx.h>

    int
    DbEnv::set_tx_max(u_int32_t max);

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 DbEnv::txn_begin() will fail (until some active transactions complete). If `DbEnv::set_tx_max()` 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 `DbEnv::set_tx_max()` method configures a database environment, not only operations performed using the specified DbEnv handle.

The `DbEnv::set_tx_max()` method may not be called after the DbEnv::open() method is called. If the database environment already exists when DbEnv::open() is called, the information specified to `DbEnv::set_tx_max()` will be ignored.

The `DbEnv::set_tx_max()` method either returns a non-zero error value or throws an exception that encapsulates a non-zero error value on failure, and returns 0 on success.

### Parameters

#### max

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

### Errors

The `DbEnv::set_tx_max()` method may fail and throw a DbException exception, encapsulating one of the following non-zero errors, or return one of the following non-zero errors:

#### EINVAL

If the method was called after DbEnv::open() was called; or if an invalid flag value or parameter was specified.

### Class

DbEnv, DbTxn

### See Also

Transaction Subsystem and Related Methods

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