Why there is a berkeleydb auto inserted record using secondary db?

Question

Hi all,
I using secondary db to do multi-key query, but I find berkeyleydb insert a dummy record automatically and this dummy record can be queried out using cursor, which is quite annoying.
Below is my code example:
Init(const char *pszPath)
     try
          char szFileName[256] = "";
          if (strlen(m_szPath) > 0)
               sprintf(szFileName, "%s%s", m_szPath, "qmdb_Positions.db");
          else
               strcpy(szFileName, "qmdb_Positions.db");
          char *pszFileName = NULL;
          if (strcmp("file", "none") == 0)
               pszFileName = szFileName;
          m_pDBPositions = new Db(NULL, 0);
          m_pDBPositions->open(NULL, pszFileName, szFileName, DB_BTREE, DB_CREATE, 0);
          m_pSeqPositions = new DbSequence(m_pDBPositions, 0);
          Dbt key((void *)m_SeqNamePositions, (u_int32_t)strlen(m_SeqNamePositions));
          m_pSeqPositions->open(NULL, &key, DB_CREATE);
          m_pIdxInstrument = new Db(NULL, 0);
          m_pIdxInstrument->set_flags(DB_DUPSORT);
          if (strlen(m_szPath) > 0)
               sprintf(szFileName, "%s%s", m_szPath, "qmdbs_Positions_Instrument.db");
          else
               strcpy(szFileName, "qmdbs_Positions_Instrument.db");
          m_pIdxInstrument->open(NULL, pszFileName, szFileName, DB_BTREE, DB_CREATE, 0);
          m_pDBPositions->associate(NULL, m_pIdxInstrument, &qmPositionsTable::ExtractInstrument, 0);
          m_pIdxDirection = new Db(NULL, 0);
          m_pIdxDirection->set_flags(DB_DUPSORT);
          if (strlen(m_szPath) > 0)
               sprintf(szFileName, "%s%s", m_szPath, "qmdbs_Positions_Direction.db");
          else
               strcpy(szFileName, "qmdbs_Positions_Direction.db");
          m_pIdxDirection->open(NULL, pszFileName, szFileName, DB_BTREE, DB_CREATE, 0);
          m_pDBPositions->associate(NULL, m_pIdxDirection, &qmPositionsTable::ExtractDirection, 0);
          Dbc pCursor = NULL;
          m_pDBPositions->cursor(NULL, &pCursor, 0);
          Dbt k, data;
          if (DB_NOTFOUND != pCursor->get(&k, &data, DB_NEXT))
               qmPositionsRecord record;
               memcpy(&record, data.get_data(), sizeof(qmPositionsRecord));
               printf("%s", record.Instrument);
     catch (DbException &e)
          string error = e.what();
     catch (std::exception &e)
     return 0;
int qmPositionsTable::
ExtractInstrument(Db dbp, const Dbt pkey, const Dbt pdata, Dbt skey)
     qmPositionsRecord *pRecord;
     pRecord = (qmPositionsRecord *)pdata->get_data();
     skey->set_data((void *)GetAddressOfInstrument(pRecord->Instrument));
     skey->set_size(GetLengthOfInstrument(pRecord->Instrument));
     return 0;
int qmPositionsTable::
ExtractDirection(Db dbp, const Dbt pkey, const Dbt pdata, Dbt skey)
     qmPositionsRecord *pRecord;
     pRecord = (qmPositionsRecord *)pdata->get_data();
     skey->set_data((void *)GetAddressOfDirection(pRecord->Direction));
     skey->set_size(GetLengthOfDirection(pRecord->Direction));
     return 0;
Edited by: Bruce on 2012-5-8 下午11:14

Answer 1

In your scenario record will be deleted as your DB Poller will commit the transaction once the message has been delivered to Proxy Service A.
If you want the message not to be deleted then you must have only the DB Poller proxy include the logic of proxy A and must make a call to proxy B.