本示例演示了 NDB API 事件处理。

此程序的源代码可以在 NDB 集群源代码树中的 storage/ndb/ndbapi-examples/ndbapi_event/ndbapi_event.cpp 文件中找到。

#include <NdbApi.hpp>

// Used for cout
#include <stdio.h>
#include <iostream>
#include <unistd.h>
#ifdef VM_TRACE
#include <my_global.h>
#endif
#ifndef assert
#include <assert.h>
#endif


/**
 * Assume that there is a table which is being updated by
 * another process (e.g. flexBench -l 0 -stdtables).
 * We want to monitor what happens with column values.
 *
 * Or using the mysql client:
 *
 * $> mysql -u root
 * mysql> create database ndb_examples;
 * mysql> use ndb_examples;
 * mysql> create table t0
          (c0 int, c1 int, c2 char(4), c3 char(4), c4 text,
          primary key(c0, c2)) engine ndb charset latin1;
 *
 * In another window start ndbapi_event, wait until properly started

   insert into t0 values (1, 2, 'a', 'b', null);
   insert into t0 values (3, 4, 'c', 'd', null);
   update t0 set c3 = 'e' where c0 = 1 and c2 = 'a'; -- use pk
   update t0 set c3 = 'f'; -- use scan
   update t0 set c3 = 'F'; -- use scan update to 'same'
   update t0 set c2 = 'g' where c0 = 1; -- update pk part
   update t0 set c2 = 'G' where c0 = 1; -- update pk part to 'same'
   update t0 set c0 = 5, c2 = 'H' where c0 = 3; -- update full PK
   delete from t0;

   insert ...; update ...; -- see events w/ same pk merged (if -m option)
   delete ...; insert ...; -- there are 5 combinations ID IU DI UD UU
   update ...; update ...;

   -- text requires -m flag
   set @a = repeat('a',256); -- inline size
   set @b = repeat('b',2000); -- part size
   set @c = repeat('c',2000*30); -- 30 parts

   -- update the text field using combinations of @a, @b, @c ...

 * you should see the data popping up in the example window
 *
 */

#define APIERROR(error) \
  { std::cout << "Error in " << __FILE__ << ", line:" << __LINE__ << ", code:" \
              << error.code << ", msg: " << error.message << "." << std::endl; \
    exit(-1); }

int myCreateEvent(Ndb* myNdb,
		  const char *eventName,
		  const char *eventTableName,
		  const char **eventColumnName,
		  const int noEventColumnName,
                  bool merge_events);

int main(int argc, char** argv)
{
  if (argc < 3)
  {
    std::cout << "Arguments are <connect_string cluster> <timeout> [m(merge events)|d(debug)].\n";
    exit(-1);
  }
  const char *connection_string = argv[1];
  int timeout = atoi(argv[2]);
  ndb_init();
  bool merge_events = argc > 3 && strchr(argv[3], 'm') != 0;
#ifdef VM_TRACE
  bool dbug = argc > 3 && strchr(argv[3], 'd') != 0;
  if (dbug) DBUG_PUSH("d:t:");
  if (dbug) putenv("API_SIGNAL_LOG=-");
#endif

  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);
  }

  Ndb* myNdb= new Ndb(cluster_connection,
		      "ndb_examples");  // Object representing the database

  if (myNdb->init() == -1) APIERROR(myNdb->getNdbError());

  const char *eventName= "CHNG_IN_t0";
  const char *eventTableName= "t0";
  const int noEventColumnName= 5;
  const char *eventColumnName[noEventColumnName]=
    {"c0",
     "c1",
     "c2",
     "c3",
     "c4"
    };

  // Create events
  myCreateEvent(myNdb,
		eventName,
		eventTableName,
		eventColumnName,
		noEventColumnName,
                merge_events);

  // Normal values and blobs are unfortunately handled differently..
  typedef union { NdbRecAttr* ra; NdbBlob* bh; } RA_BH;

  int i, j, k, l;
  j = 0;
  while (j < timeout) {

    // Start "transaction" for handling events
    NdbEventOperation* op;
    printf("create EventOperation\n");
    if ((op = myNdb->createEventOperation(eventName)) == NULL)
      APIERROR(myNdb->getNdbError());
    op->mergeEvents(merge_events);

    printf("get values\n");
    RA_BH recAttr[noEventColumnName];
    RA_BH recAttrPre[noEventColumnName];
    // primary keys should always be a part of the result
    for (i = 0; i < noEventColumnName; i++) {
      if (i < 4) {
        recAttr[i].ra    = op->getValue(eventColumnName[i]);
        recAttrPre[i].ra = op->getPreValue(eventColumnName[i]);
      } else if (merge_events) {
        recAttr[i].bh    = op->getBlobHandle(eventColumnName[i]);
        recAttrPre[i].bh = op->getPreBlobHandle(eventColumnName[i]);
      }
    }

    // set up the callbacks
    printf("execute\n");
    // This starts changes to "start flowing"
    if (op->execute())
      APIERROR(op->getNdbError());

    NdbEventOperation* the_op = op;

    i= 0;
    while (i < timeout) {
      // printf("now waiting for event...\n");
      int r = myNdb->pollEvents(1000); // wait for event or 1000 ms
      if (r > 0) {
	// printf("got data! %d\n", r);
	while ((op= myNdb->nextEvent())) {
          assert(the_op == op);
	  i++;
	  switch (op->getEventType()) {
	  case NdbDictionary::Event::TE_INSERT:
	    printf("%u INSERT", i);
	    break;
	  case NdbDictionary::Event::TE_DELETE:
	    printf("%u DELETE", i);
	    break;
	  case NdbDictionary::Event::TE_UPDATE:
	    printf("%u UPDATE", i);
	    break;
	  default:
	    abort(); // should not happen
	  }
          printf(" gci=%d\n", (int)op->getGCI());
          for (k = 0; k <= 1; k++) {
            printf(k == 0 ? "post: " : "pre : ");
            for (l = 0; l < noEventColumnName; l++) {
              if (l < 4) {
                NdbRecAttr* ra = k == 0 ? recAttr[l].ra : recAttrPre[l].ra;
                if (ra->isNULL() >= 0) { // we have a value
                  if (ra->isNULL() == 0) { // we have a non-null value
                    if (l < 2)
                      printf("%-5u", ra->u_32_value());
                    else
                      printf("%-5.4s", ra->aRef());
                  } else
                    printf("%-5s", "NULL");
                } else
                  printf("%-5s", "-"); // no value
              } else if (merge_events) {
                int isNull;
                NdbBlob* bh = k == 0 ? recAttr[l].bh : recAttrPre[l].bh;
                bh->getDefined(isNull);
                if (isNull >= 0) { // we have a value
                  if (! isNull) { // we have a non-null value
                    Uint64 length = 0;
                    bh->getLength(length);
                    // read into buffer
                    unsigned char* buf = new unsigned char [length];
                    memset(buf, 'X', length);
                    Uint32 n = length;
                    bh->readData(buf, n); // n is in/out
                    assert(n == length);
                    // pretty-print
                    bool first = true;
                    Uint32 i = 0;
                    while (i < n) {
                      unsigned char c = buf[i++];
                      Uint32 m = 1;
                      while (i < n && buf[i] == c)
                        i++, m++;
                      if (! first)
                        printf("+");
                      printf("%u%c", m, c);
                      first = false;
                    }
                    printf("[%u]", n);
                    delete [] buf;
                  } else
                    printf("%-5s", "NULL");
                } else
                  printf("%-5s", "-"); // no value
              }
            }
            printf("\n");
          }
	}
      } // else printf("timed out (%i)\n", timeout);
    }
    // don't want to listen to events anymore
    if (myNdb->dropEventOperation(the_op)) APIERROR(myNdb->getNdbError());
    the_op = 0;

    j++;
  }

  {
    NdbDictionary::Dictionary *myDict = myNdb->getDictionary();
    if (!myDict) APIERROR(myNdb->getNdbError());
    // remove event from database
    if (myDict->dropEvent(eventName)) APIERROR(myDict->getNdbError());
  }

  delete myNdb;
  delete cluster_connection;
  ndb_end(0);
  return 0;
}

int myCreateEvent(Ndb* myNdb,
		  const char *eventName,
		  const char *eventTableName,
		  const char **eventColumnNames,
		  const int noEventColumnNames,
                  bool merge_events)
{
  NdbDictionary::Dictionary *myDict= myNdb->getDictionary();
  if (!myDict) APIERROR(myNdb->getNdbError());

  const NdbDictionary::Table *table= myDict->getTable(eventTableName);
  if (!table) APIERROR(myDict->getNdbError());

  NdbDictionary::Event myEvent(eventName, *table);
  myEvent.addTableEvent(NdbDictionary::Event::TE_ALL);
  //  myEvent.addTableEvent(NdbDictionary::Event::TE_INSERT);
  //  myEvent.addTableEvent(NdbDictionary::Event::TE_UPDATE);
  //  myEvent.addTableEvent(NdbDictionary::Event::TE_DELETE);

  myEvent.addEventColumns(noEventColumnNames, eventColumnNames);
  myEvent.mergeEvents(merge_events);

  // Add event to database
  if (myDict->createEvent(myEvent) == 0)
    myEvent.print();
  else if (myDict->getNdbError().classification ==
	   NdbError::SchemaObjectExists) {
    printf("Event creation failed, event exists\n");
    printf("dropping Event...\n");
    if (myDict->dropEvent(eventName)) APIERROR(myDict->getNdbError());
    // try again
    // Add event to database
    if ( myDict->createEvent(myEvent)) APIERROR(myDict->getNdbError());
  } else
    APIERROR(myDict->getNdbError());

  return 0;
}