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This program demonstrates handling errors and retrying failed transactions using the NDB API.

The source code for this example can be found instorage/ndb/ndbapi-examples/ndbapi_retries/ndbapi_retries.cpp in the NDB Cluster source tree.

There are many ways to program using the NDB API. In this example, we perform two inserts in the same transaction usingNdbTransaction::execute(NoCommit).

In NDB API applications, there are two types of failures to be taken into account:

////  ndbapi_retries.cpp: Error handling and transaction retries////  There are many ways to program using the NDB API.  In this example//  we execute two inserts in the same transaction using//  NdbConnection::execute(NoCommit).////  Transaction failing is handled by re-executing the transaction//  in case of non-permanent transaction errors.//  Application errors (i.e. errors at points marked with APIERROR)//  should be handled by the application programmer.#include <mysql.h>#include <mysqld_error.h>#include <NdbApi.hpp>// Used for cout#include <iostream>// Used for sleep (use your own version of sleep)#include <unistd.h>#define TIME_TO_SLEEP_BETWEEN_TRANSACTION_RETRIES 1#define PRINT_ERROR(code,msg) \  std::cout << "Error in " << __FILE__ << ", line: " << __LINE__ \            << ", code: " << code \            << ", msg: " << msg << "." << std::endl#define MYSQLERROR(mysql) { \  PRINT_ERROR(mysql_errno(&mysql),mysql_error(&mysql)); \  exit(-1); }////  APIERROR prints an NdbError object//#define APIERROR(error) \  { std::cout << "API ERROR: " << error.code << " " << error.message \              << std::endl \              << "           " << "Status: " << error.status \              << ", Classification: " << error.classification << std::endl\              << "           " << "File: " << __FILE__ \              << " (Line: " << __LINE__ << ")" << std::endl \              ; \  }////  TRANSERROR prints all error info regarding an NdbTransaction//#define TRANSERROR(ndbTransaction) \  { NdbError error = ndbTransaction->getNdbError(); \    std::cout << "TRANS ERROR: " << error.code << " " << error.message \              << std::endl \              << "           " << "Status: " << error.status \              << ", Classification: " << error.classification << std::endl \              << "           " << "File: " << __FILE__ \              << " (Line: " << __LINE__ << ")" << std::endl \              ; \    printTransactionError(ndbTransaction); \  }void printTransactionError(NdbTransaction *ndbTransaction) {  const NdbOperation *ndbOp = NULL;  int i=0;  /****************************************************************   * Print NdbError object of every operations in the transaction *   ****************************************************************/  while ((ndbOp = ndbTransaction->getNextCompletedOperation(ndbOp)) != NULL) {    NdbError error = ndbOp->getNdbError();    std::cout << "           OPERATION " << i+1 << ": "      << error.code << " " << error.message << std::endl      << "           Status: " << error.status      << ", Classification: " << error.classification << std::endl;    i++;  }}////  Example insert//  @param myNdb          Ndb object representing NDB Cluster//  @param myTransaction  NdbTransaction used for transaction//  @param myTable        Table to insert into//  @param error          NdbError object returned in case of errors//  @return -1 in case of failures, 0 otherwise//int insert(int transactionId, NdbTransaction* myTransaction,   const NdbDictionary::Table *myTable) {  NdbOperation *myOperation;          // For other operations  myOperation = myTransaction->getNdbOperation(myTable);  if (myOperation == NULL) return -1;  if (myOperation->insertTuple() ||      myOperation->equal("ATTR1", transactionId) ||      myOperation->setValue("ATTR2", transactionId)) {    APIERROR(myOperation->getNdbError());    exit(-1);  }  return myTransaction->execute(NdbTransaction::NoCommit);}////  Execute function which re-executes (tries 10 times) the transaction//  if there are temporary errors (e.g. the NDB Cluster is overloaded).//  @return -1 failure, 1 success//int executeInsertTransaction(int transactionId, Ndb* myNdb,     const NdbDictionary::Table *myTable) {  int result = 0;                       // No result yet  int noOfRetriesLeft = 10;  NdbTransaction *myTransaction;         // For other transactions  NdbError ndberror;  while (noOfRetriesLeft > 0 && !result) {    /*********************************     * Start and execute transaction *     *********************************/    myTransaction = myNdb->startTransaction();    if (myTransaction == NULL) {      APIERROR(myNdb->getNdbError());      ndberror = myNdb->getNdbError();      result = -1;  // Failure    } else if (insert(transactionId, myTransaction, myTable) ||       insert(10000+transactionId, myTransaction, myTable) ||       myTransaction->execute(NdbTransaction::Commit)) {      TRANSERROR(myTransaction);      ndberror = myTransaction->getNdbError();      result = -1;  // Failure    } else {      result = 1;   // Success    }    /**********************************     * If failure, then analyze error *     **********************************/    if (result == -1) {      switch (ndberror.status) {      case NdbError::Success:break;      case NdbError::TemporaryError:std::cout << "Retrying transaction..." << std::endl;sleep(TIME_TO_SLEEP_BETWEEN_TRANSACTION_RETRIES);--noOfRetriesLeft;result = 0;   // No completed transaction yetbreak;      case NdbError::UnknownResult:      case NdbError::PermanentError:std::cout << "No retry of transaction..." << std::endl;result = -1;  // Permanent failurebreak;      }    }    /*********************     * Close transaction *     *********************/    if (myTransaction != NULL) {      myNdb->closeTransaction(myTransaction);    }  }  if (result != 1) exit(-1);  return result;}/********************************************************* * Create a table named api_retries if it does not exist * *********************************************************/static void create_table(MYSQL &mysql){  while(mysql_query(&mysql,  "CREATE TABLE "  "  api_retries"  "    (ATTR1 INT UNSIGNED NOT NULL PRIMARY KEY,"  "     ATTR2 INT UNSIGNED NOT NULL)"  "  ENGINE=NDB"))  {    if (mysql_errno(&mysql) == ER_TABLE_EXISTS_ERROR)    {      std::cout << "NDB Cluster already has example table: api_scan. "     << "Dropping it..." << std::endl;        mysql_query(&mysql, "DROP TABLE api_retries");    }    else MYSQLERROR(mysql);  }}int main(int argc, char** argv){  if (argc != 3)  {    std::cout << "Arguments are <socket mysqld> <connect_string cluster>.\n";    exit(-1);  }  char * mysqld_sock  = argv[1];  const char *connection_string = argv[2];  ndb_init();  Ndb_cluster_connection *cluster_connection=    new Ndb_cluster_connection(connection_string); // Object representing the cluster  int r= cluster_connection->connect(5 /* retries               */,     3 /* delay between retries */,     1 /* verbose               */);  if (r > 0)  {    std::cout      << "Cluster connect failed, possibly resolved with more retries.\n";    exit(-1);  }  else if (r < 0)  {    std::cout      << "Cluster connect failed.\n";    exit(-1);  }  if (cluster_connection->wait_until_ready(30,30))  {    std::cout << "Cluster was not ready within 30 secs." << std::endl;    exit(-1);  }  // connect to mysql server  MYSQL mysql;  if ( !mysql_init(&mysql) ) {    std::cout << "mysql_init failed\n";    exit(-1);  }  if ( !mysql_real_connect(&mysql, "localhost", "root", "", "",   0, mysqld_sock, 0) )    MYSQLERROR(mysql);  /********************************************   * Connect to database via mysql-c          *   ********************************************/  mysql_query(&mysql, "CREATE DATABASE ndb_examples");  if (mysql_query(&mysql, "USE ndb_examples") != 0) MYSQLERROR(mysql);  create_table(mysql);  mysql_close(&mysql);  Ndb* myNdb= new Ndb( cluster_connection,       "ndb_examples" );  // Object representing the database  if (myNdb->init() == -1) {    APIERROR(myNdb->getNdbError());    exit(-1);  }  const NdbDictionary::Dictionary* myDict= myNdb->getDictionary();  const NdbDictionary::Table *myTable= myDict->getTable("api_retries");  if (myTable == NULL)  {    APIERROR(myDict->getNdbError());    return -1;  }  /************************************   * Execute some insert transactions *   ************************************/  std::cout << "Ready to insert rows.  You will see notices for temporary "    "errors, permenant errors, and retries. \n";  for (int i = 10000; i < 20000; i++) {    executeInsertTransaction(i, myNdb, myTable);  }  std::cout << "Done.\n";  delete myNdb;  delete cluster_connection;  ndb_end(0);  return 0;}