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MySQL NDB Cluster API Developer Guide  /  The MGM API  /  MGM API Concepts

3.1 MGM API Concepts

Each MGM API function needs a management server handle of type NdbMgmHandle. This handle is created by calling the function ndb_mgm_create_handle() and freed by calling ndb_mgm_destroy_handle().

See Section 3.2.3.1, “ndb_mgm_create_handle()”, and Section 3.2.3.4, “ndb_mgm_destroy_handle()”, for more information about these two functions.

Important

You should not share an NdbMgmHandle between threads. While it is possible to do so (if you implement your own locks), this is not recommended; each thread should use its own management server handle.

A function can return any of the following:

  • An integer value, with a value of -1 indicating an error.

  • A nonconstant pointer value. A NULL value indicates an error; otherwise, the return value must be freed by the programmer.

  • A constant pointer value, with a NULL value indicating an error. The returned value should not be freed.

Error conditions can be identified by using the appropriate error-reporting functions ndb_mgm_get_latest_error() and ndb_mgm_error().

Here is an example using the MGM API (without error handling for brevity's sake):

NdbMgmHandle handle= ndb_mgm_create_handle();
ndb_mgm_connect(handle,0,0,0);
struct ndb_mgm_cluster_state *state= ndb_mgm_get_status(handle);
for(int i=0; i < state->no_of_nodes; i++)
{
  struct ndb_mgm_node_state *node_state= &state->node_states[i];
  printf("node with ID=%d ", node_state->node_id);

  if(node_state->version != 0)
    printf("connected\n");
  else
    printf("not connected\n");
}
free((void*)state);
ndb_mgm_destroy_handle(&handle);

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