Berkeley DB: txn_begin
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++

# txn_begin |

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    #include <db.h>

    int
    txn_begin(DB_ENV *env,
    	DB_TXN *parent, DB_TXN **tid, u_int32_t flags);

# Description

The txn_begin method creates a new transaction in the environment and copies a pointer to a DB_TXN that uniquely identifies it into the memory referenced by tid.

If the parent argument is non-NULL, the new transaction will be a nested transaction, with the transaction indicated by parent as its parent. Transactions may be nested to any level.

The flags parameter must be set to 0 or one of the following values:

DB_TXN_NOSYNC
  Do not synchronously flush the log when this transaction commits or prepares. This means the transaction will exhibit the ACI (atomicity, consistency and isolation) properties, but not D (durability), i.e., database integrity will be maintained but it is possible that this transaction may be undone during recovery instead of being redone.

  This behavior may be set for an entire Berkeley DB environment as part of the DBENV->open interface.

DB_TXN_NOWAIT
  If a lock is unavailable for any Berkeley DB operation performed in the context of this transaction, return immediately instead of blocking on the lock. The error return in the case will be DB_LOCK_NOTGRANTED.

DB_TXN_SYNC
  Synchronously flush the log when this transaction commits or prepares. This means the transaction will exhibit all of the ACID (atomicity, consistency and isolation and durability) properties.

  This behavior is the default for Berkeley DB environments unless the DB_TXN_NOSYNC flag was specified to the DBENV->open interface.

Note: transactions may not span threads, i.e., each transaction must begin and end in the same thread, and each transaction may only be used by a single thread.

Note: cursors may not span transactions, i.e., each cursor must be opened and closed within a single transaction.

Note: a parent transaction may not issue any Berkeley DB operations, except for txn_begin, txn_abort and txn_commit, while it has active child transactions (child transactions that have not yet been committed or aborted).

The txn_begin function returns a non-zero error value on failure and 0 on success.

# Errors

The txn_begin function may fail and return a non-zero error for the following conditions:

ENOMEM
  The maximum number of concurrent transactions has been reached.

The txn_begin function 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 txn_begin function may fail and return DB_RUNRECOVERY, in which case all subsequent Berkeley DB calls will fail in the same way.

# See Also

DBENV->set_tx_max, DBENV->set_tx_recover, DBENV->set_tx_timestamp, txn_abort, txn_begin, txn_checkpoint, txn_commit, txn_id, txn_prepare and txn_stat.`

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