Dbc::get() has no need to commit ?

Question

m_pEvironment->txn_begin (NULL,&m_pTransaction,0);
     nRes=m_pDb->cursor (m_pTransaction,&m_pCursor,0);
     try
          Dbt dbKey;     
          Dbt dbData;               
          int nRes;
          dbKey.set_flags (DB_DBT_MALLOC);
          dbData.set_flags (DB_DBT_MALLOC);
          nRes=m_pCursor->get (&dbKey,&dbData,DB_NEXT);
          m_pTransaction->commit (0); // <---------exception catched ,jump to catch() block.
          // Dbc::get() is one of a access operation ,in theory it need a commitment.
     catch (DbException &dbe)
sorry to disturb you as I really have no information to refer to.

Answer 1

First, you need to close the cursor before commiting or aborting the transaction. Here is a sample used in the Berkeley DB Transaction Guide:
#include <stdio.h>
#include <stdlib.h>
#include "db.h"
int
main(void)
DBT key, data;
DBC *cursorp;
DB_TXN *txn = NULL;
int ret, c_ret;
char *replacementString = "new string";
/* environment and db handle creation omitted */
/* Get the txn handle */
txn = NULL;
ret = envp->txn_begin(envp, NULL, &txn, 0);
if (ret != 0) {
envp->err(envp, ret, "Transaction begin failed.");
goto err;
/* Get the cursor, supply the txn handle at that time */
ret = dbp->cursor(dbp, txn, &cursorp, 0);
if (ret != 0) {
envp->err(envp, ret, "Cursor open failed.");
txn->abort(txn);
goto err;
* Now use the cursor. Note that we do not supply any txn handles to these
* methods.
/* Prepare the DBTs */
memset(&key, 0, sizeof(DBT));
memset(&data, 0, sizeof(DBT));
while (cursor->c_get(&key, &data, DB_NEXT) == 0) {
data->data = (void *)replacementString;
data->size = (strlen(replacementString) + 1) * sizeof(char);
c_ret = cursor->c_put(cursor, &key, &data, DB_CURRENT);
if (c_ret != 0) {
/* abort the transaction and goto error */
envp->err(envp, ret, "Cursor put failed.");
cursorp->c_close(cursorp);
cursorp = NULL;
txn->abort(txn);
goto err;
* Commit the transaction. Note that the transaction handle
* can no longer be used.
ret = cursorp->c_close(cursorp);
if (ret != 0) {
envp->err(envp, ret, "Cursor close failed.");
txn->abort(txn);
goto err;
ret = txn->commit(txn, 0);
if (ret != 0) {
envp->err(envp, ret, "Transaction commit failed.");
goto err;
err:
/* Close the cursor (if the handle is not NULL)
* and perform whatever other cleanup is required */
/* Close the database */
/* Close the environment */
if (c_ret != 0)
ret = c_ret;
return (ret == 0 ? EXIT_SUCCESS : EXIT_FAILURE);
Ron