Что значимо для formatID в структуре XID в библиотеке OCI?

Question

Я очень новичок в библиотеке OCI. Я пытался исследовать библиотеку OCI. Я нашел пример кода на официальном сайте для создания транзакции с использованием C.

1) Я просто хочу узнать значение поля formatID в структуре XID в примере кода.

2) Каким может быть значение formatID ?

3) Можно ли использовать одно и то же значение в formatID в двух последовательных транзакциях?

4) Если я открываю два соединения и два соединения создаю две транзакции, могу ли я использовать один и тот же formatID для этих двух транзакций?

int main()
{
  OCIEnv *envhp;
  OCIServer *srvhp;
  OCIError *errhp;
  OCISvcCtx *svchp;
  OCISession *usrhp;
  OCIStmt *stmthp1, *stmthp2;
  OCITrans *txnhp1, *txnhp2;
  dvoid     *tmp;
  XID gxid;
  text sqlstmt[128];

  OCIInitialize((ub4) OCI_OBJECT, (dvoid *)0,  (dvoid * (*)()) 0,
             (dvoid * (*)()) 0,  (void (*)()) 0 );

  OCIHandleAlloc( (dvoid *) NULL, (dvoid **) &envhp, (ub4) OCI_HTYPE_ENV,
             0, (dvoid **) &tmp);

  OCIEnvInit( &envhp, (ub4) OCI_DEFAULT, 21, (dvoid **) &tmp  );

  OCIHandleAlloc( (dvoid *) envhp, (dvoid **) &errhp, (ub4) OCI_HTYPE_ERROR,
                52, (dvoid **) &tmp);
  OCIHandleAlloc( (dvoid *) envhp, (dvoid **) &srvhp, (ub4) OCI_HTYPE_SERVER,
                52, (dvoid **) &tmp);

  OCIServerAttach( srvhp, errhp, (text *) 0, (sb4) 0, (ub4) OCI_DEFAULT);

  OCIHandleAlloc( (dvoid *) envhp, (dvoid **) &svchp, (ub4) OCI_HTYPE_SVCCTX,
                52, (dvoid **) &tmp);

  OCIHandleAlloc((dvoid *)envhp, (dvoid **)&stmthp1, OCI_HTYPE_STMT, 0, 0);
  OCIHandleAlloc((dvoid *)envhp, (dvoid **)&stmthp2, OCI_HTYPE_STMT, 0, 0);

  OCIAttrSet((dvoid *)svchp, OCI_HTYPE_SVCCTX, (dvoid *)srvhp, 0,
                  OCI_ATTR_SERVER, errhp);

  /* set the external name and internal name in server handle */
  OCIAttrSet((dvoid *)srvhp, OCI_HTYPE_SERVER, (dvoid *) "demo", 0,
                  OCI_ATTR_EXTERNAL_NAME, errhp);
  OCIAttrSet((dvoid *)srvhp, OCI_HTYPE_SERVER, (dvoid *) "txn demo", 0,
                          OCI_ATTR_INTERNAL_NAME, errhp);

  /* allocate a user context handle */
  OCIHandleAlloc((dvoid *)envhp, (dvoid **)&usrhp, (ub4) OCI_HTYPE_SESSION,
                (size_t) 0, (dvoid **) 0);

  OCIAttrSet((dvoid *)usrhp, (ub4)OCI_HTYPE_SESSION, (dvoid *)"scott", 
             (ub4)strlen("scott"), OCI_ATTR_USERNAME, errhp);
  OCIAttrSet((dvoid *)usrhp, (ub4)OCI_HTYPE_SESSION, (dvoid *)"tiger", 
             (ub4)strlen("tiger"),OCI_ATTR_PASSWORD, errhp);

  OCISessionBegin (svchp, errhp, usrhp, OCI_CRED_RDBMS, 0);

  OCIAttrSet((dvoid *)svchp, (ub4)OCI_HTYPE_SVCCTX,
                (dvoid *)usrhp, (ub4)0, OCI_ATTR_SESSION, errhp);

  /* allocate transaction handle 1 and set it in the service handle */
  OCIHandleAlloc((dvoid *)envhp, (dvoid **)&txnhp1,  OCI_HTYPE_TRANS, 0, 0);
  OCIAttrSet((dvoid *)svchp, OCI_HTYPE_SVCCTX, (dvoid *)txnhp1, 0,
                          OCI_ATTR_TRANS, errhp);

  /* start a transaction with global transaction id = [1000, 123, 1] */
  gxid.formatID = 1000; /* format id = 1000 */
  gxid.gtrid_length = 3; /* gtrid = 123 */
  gxid.data[0] = 1; gxid.data[1] = 2; gxid.data[2] = 3;
  gxid.bqual_length = 1; /* bqual = 1 */
  gxid.data[3] = 1;

  OCIAttrSet((dvoid *)txnhp1, OCI_HTYPE_TRANS, (dvoid *)&gxid, sizeof(XID),
                          OCI_ATTR_XID, errhp);

  /* start global transaction 1 with 60 second time to live when detached */
  OCITransStart(svchp, errhp, 60, OCI_TRANS_NEW);

  /* update scott.emp empno=7902, increment salary */
  sprintf((char *)sqlstmt, "UPDATE EMP SET SAL = SAL + 1 WHERE EMPNO = 7902");
  OCIStmtPrepare(stmthp1, errhp, sqlstmt, strlen(sqlstmt), OCI_NTV_SYNTAX, 0);
  OCIStmtExecute(svchp, stmthp1, errhp, 1, 0, 0, 0, 0);

  /* detach the transaction */
  OCITransDetach(svchp, errhp, 0);

  /* allocate transaction handle 2 and set it in the service handle */
  OCIHandleAlloc((dvoid *)envhp, (dvoid **)&txnhp2,  OCI_HTYPE_TRANS, 0, 0);
  OCIAttrSet((dvoid *)svchp, OCI_HTYPE_SVCCTX, (dvoid *)txnhp2, 0,
                          OCI_ATTR_TRANS, errhp);

  /* start a transaction with global transaction id = [1000, 124, 1] */
  gxid.formatID = 1000; /* format id = 1000 */
  gxid.gtrid_length = 3; /* gtrid = 124 */
  gxid.data[0] = 1; gxid.data[1] = 2; gxid.data[2] = 4;
  gxid.bqual_length = 1; /* bqual = 1 */
  gxid.data[3] = 1; 

  OCIAttrSet((dvoid *)txnhp2, OCI_HTYPE_TRANS, (dvoid *)&gxid, sizeof(XID),
                          OCI_ATTR_XID, errhp);

  /* start global transaction 2 with 90 second time to live when detached */
  OCITransStart(svchp, errhp, 90, OCI_TRANS_NEW);

  /* update scott.emp empno=7934, increment salary */
  sprintf((char *)sqlstmt, "UPDATE EMP SET SAL = SAL + 1 WHERE EMPNO = 7934");
  OCIStmtPrepare(stmthp2, errhp, sqlstmt, strlen(sqlstmt), OCI_NTV_SYNTAX, 0);
  OCIStmtExecute(svchp, stmthp2, errhp, 1, 0, 0, 0, 0);

  /* detach the transaction */
  OCITransDetach(svchp, errhp, 0);

  /* Resume transaction 1, increment salary and commit it */
  /* Set transaction handle 1 into the service handle */
  OCIAttrSet((dvoid *)svchp, OCI_HTYPE_SVCCTX, (dvoid *)txnhp1, 0,
                          OCI_ATTR_TRANS, errhp);

  /* attach to transaction 1, wait for 10 seconds if the transaction is busy */
  /* The wait is clearly not required in this example because no other      */
  /* process/thread is using the transaction. It is only for illustration    */
  OCITransStart(svchp, errhp, 10, OCI_TRANS_RESUME);
  OCIStmtExecute(svchp, stmthp1, errhp, 1, 0, 0, 0, 0);
  OCITransCommit(svchp, errhp, (ub4) 0);

  /* attach to transaction 2 and commit it */
  /* set transaction handle2 into the service handle */
  OCIAttrSet((dvoid *)svchp, OCI_HTYPE_SVCCTX, (dvoid *)txnhp2, 0,
                          OCI_ATTR_TRANS, errhp);
  OCITransCommit(svchp, errhp, (ub4) 0);
}