Berkeley DB: DbEnv::set_tx_max
Description: Berkeley DB: An embedded database programmatic toolkit.
Keywords: embedded,database,programmatic,toolkit,b+tree,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 tx_max);

# Description

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 DbEnv::txn_begin will fail (until some active transactions complete). If no value is specified, a default value of 20 is used.

The DbEnv::set_tx_max method configures a database environment, not only operations performed using the specified DbEnv handle.

The DbEnv::set_tx_max interface may not be called after the DbEnv::open interface 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.

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.

# Errors

The DbEnv::set_tx_max method may fail and throw an exception or return a non-zero error for the following conditions:

EINVAL
  An invalid flag value or parameter was specified.

  Called after DbEnv::open was called.

The DbEnv::set_tx_max method may fail and throw an exception or return a non-zero error for errors specified for other Berkeley DB and C library or system methods. If a catastrophic error has occurred, the DbEnv::set_tx_max method may fail and either return DB_RUNRECOVERY or throw a DbRunRecoveryException, in which case all subsequent Berkeley DB calls will fail in the same way.

# Class

DbEnv, DbTxn

# See Also

Transaction Subsystem and Related Methods`

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