Data errors are errors received from the cluster as a result of a requested operation on a given item. For example, if an lcb_get() is performed on a key that does not exist, the callback will receive an LCB_KEY_ENOENT error. Other examples of conditions that can result in data errors include:

• Adding a key that already exists (An LCB_KEY_EEXISTS) will be thrown
• Replacing a key that does not already exist (LCB_KEY_ENOENT)
• Appending, prepending, or incrementing an item that does not already exist (LCB_KEY_ENOENT, LCB_NOT_STORED)
• Modifying an item while specifying a CAS, where the CAS on the server has already been modified (LCB_KEY_EEXISTS).

Environmental errors related to load or network issues might be received in exceptional conditions. Although you should not receive these types of errors in normal, well-provisioned deployments, your application must be prepared to handle them and take proper action. Environmental errors are divided into the following subgroups:

• Transient. This error type indicates an environment and/or resource limitation either on the server or on the network link between the client and the server. Examples of transient errors include timeout errors or temporary failures such as LCB_ETIMEDOUT (took too long to get a reply) and LCB_ETMPFAIL (server was too busy). Transient errors are typically best handled on the application side by backing off and retrying the operation, with the intent of reducing stress on the exhausted resource. Some examples of transient error causes:
  • Insufficient cache memory on the server
  • Overutilization of the network link between the client and server or between several servers
  • Router or switch failure
  • Failover of a node
  • Overutilization of application-side CPU.
• Fatal. This error type indicates that the client has potentially entered into an irrecoverable failed state, either because of invalid user input (or client configuration), or because an administrator has modified settings on the cluster (for example, a bucket has been removed). Examples of fatal errors include LCB_AUTH_ERROR (authentication failed) and LCB_BUCKET_ENOENT (bucket does not exist).

  Fatal errors typically require inspection of the client configuration and a restart of the client application or a reversal of the change performed at the cluster. Some examples of fatal error causes:

  • Bucket does not exist.
  • Bucket password is wrong.
  • None of the nodes in the cluster are reachable.

The lcb_errflags_t enumeration defines a set of flags that are associated with each error code. These flags define the type of error. Some examples of error types:

• LCB_ERRTYPE_INPUT, which is set when a malformed parameter is passed to the library
• LCB_ERRTYPE_DATAOP, which is set when the server is unable to satisfy data constraints such as a missing key or a CAS mismatch.

The LCB_EIF_${TYPE} macros, where ${TYPE} represents one of the lcb_errflags_t flags, can be used to check whether an error is of a specific type. The following example shows how to check the return codes:

static void get_callback(lcb_t instance,
  const void *cookie, lcb_error_t err, const lcb_get_resp_t *resp)
{
  if (err == LCB_SUCCESS) {
    printf("Successfuly retrieved key!\n");
  } else if (LCB_EIFDATA(err)) {
    switch (err) {
    case LCB_KEY_ENOENT:
      printf("Key not found!\n");
      break;
    default:
      printf("Received other unhandled data error\n");
      break;
    }
  } else if (LCB_EIFTMP(err)) {
    printf("Transient error received. May retry\n");
  }
}