Berkeley DB: DbEnv::set_tx_max
Description: Berkeley DB: An embedded database programmatic toolkit.
Keywords: embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++

### DbEnv::set_tx_max |

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    #include <db_cxx.h>

    int
    DbEnv::set_tx_max(u_int32_t max);

    int
    DbEnv::get_tx_max(u_int32_t *tx_maxp);

### Description: DbEnv::set_tx_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 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 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 DbException, 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.

### Description: DbEnv::get_tx_max

The DbEnv::get_tx_max method returns the number of active transactions.

The DbEnv::get_tx_max method may be called at any time during the life of the application.

The DbEnv::get_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

tx_maxp
  The DbEnv::get_tx_max method returns the number of active transactions in tx_maxp.

### Class

DbEnv, DbTxn

### See Also

Transaction Subsystem and Related Methods`

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