private bool TryReadValue(DataStoreKeyDto object_key, string partition_id)
{
string result;
ReadReply reply;
try
{
reply = client.Read(new ReadRequest {
ObjectKey = object_key
});
if (reply.ObjectExists)
{
result = reply.Object.Val;
Console.WriteLine(">>> Read Result: " + result);
return(CompareClock(partition_id, reply.PartitionClock, object_key));
}
Console.WriteLine(">>> Object does not exist...");
return(false);
}
catch
{
// server is crashed
bool canRetryOperation = HandleCrashedServer(attached_server_id);
if (canRetryOperation)
{
Console.WriteLine(">>> Retrying <Read> after reattaching to new master");
TryReadValue(object_key, partition_id);
}
return(false);
}
}
// Change name to reflect boolean return
private bool CompareClock(string partition_id, int reply_clock, DataStoreKeyDto object_key)
{
// Do Clock related staff
int partition_highest_clock = PartitionMapping.partitionToClockMapping[partition_id];
Console.WriteLine(">>> PartitionClock=" + partition_highest_clock + ", ReplyClock=" + reply_clock);
if (reply_clock > partition_highest_clock)
{
Console.WriteLine(">>> ReplyClock > PartitionClock. Reply clock is acceptable. ");
PartitionMapping.UpdatePartitionClock(partition_id, reply_clock);
return(true);
}
else if (reply_clock < partition_highest_clock)
{
Console.WriteLine(">>> ReplyClock < PartitionClock. Waiting " + retry_time.ToString() + "And trying again...");
wait(retry_time);
return(TryReadValue(object_key, partition_id));
}
else if (reply_clock == partition_highest_clock)
{
Console.WriteLine(">>> PartitionClock == ReplyClock. Reply clock is acceptable. ");
}
return(true);
}
private void write(string partition_id, string object_id, string value)
{
WriteReply reply;
if (debug_console)
{
Console.WriteLine("Get Partition Master from Partition Named: " + partition_id);
}
string partition_master_server_id = PartitionMapping.GetPartitionMaster(partition_id);
if (debug_console)
{
Console.WriteLine("Partition Master Server ID: " + partition_master_server_id);
}
reattachServer(partition_master_server_id);
var object_key = new DataStoreKeyDto
{
PartitionId = partition_id,
ObjectId = object_id
};
var object_value = new DataStoreValueDto
{
Val = value
};
Console.WriteLine(">>> Write request...");
try
{
reply = client.Write(new WriteRequest {
ObjectKey = object_key, Object = object_value
});
Console.WriteLine("Write result: " + reply);
}
catch
{
bool canRetryOperation = HandleCrashedServer(attached_server_id);
if (canRetryOperation)
{
Console.WriteLine(">>> Retrying <Write> after reattaching to new master");
write(partition_id, object_id, value);
}
return;
}
}
private void read(string partition_id, string object_id, string server_id)
{
string result = "N/A";
bool got_result = false;
ReadReply reply;
var object_key = new DataStoreKeyDto
{
PartitionId = partition_id,
ObjectId = object_id
};
if (debug_console)
{
Console.WriteLine("Reading from the server...");
}
Console.WriteLine(">>> Read request...");
// if the client is attached to a server and that server contains the desired partition
List <string> available_partitions_in_server = PartitionMapping.getPartitionsByServerID(attached_server_id);
if (!string.IsNullOrEmpty(attached_server_id) && available_partitions_in_server.Contains(partition_id))
{
if (debug_console)
{
Console.WriteLine("Reading from the Attached Server: " + attached_server_id);
}
// read value from attached server
try
{
reply = client.Read(new ReadRequest {
ObjectKey = object_key
});
if (reply.ObjectExists)
{
result = reply.Object.Val;
got_result = true;
}
// server is crashed
} catch
{
handle_crashed_server(attached_server_id);
got_result = false;
}
}
// if theres no result yet and there is a valid server_id parameter
if ((!got_result) && (!server_id.Equals("-1")))
{
// check if the server hint even has the partition
available_partitions_in_server = PartitionMapping.getPartitionsByServerID(server_id);
if (available_partitions_in_server.Contains(partition_id))
{
if (debug_console)
{
Console.WriteLine("Attach to new Server: " + server_id);
}
reattachServer(server_id);
// read value from alternative server
try
{
reply = client.Read(new ReadRequest {
ObjectKey = object_key
});
if (reply.ObjectExists)
{
result = reply.Object.Val;
got_result = true;
}
// server is crashed
} catch
{
handle_crashed_server(attached_server_id);
got_result = false;
}
}
}
// if theres no result yet, the client should find a server serving partition_id on its own
// it will try to connect to every single node in that partition
if (!got_result)
{
string[] partition_nodes = PartitionMapping.getPartitionAllNodes(partition_id);
foreach (string node_id in partition_nodes)
{
if (debug_console)
{
Console.WriteLine("Attach to new Server: " + node_id);
}
reattachServer(node_id);
// read value from one of the partition servers
try
{
reply = client.Read(new ReadRequest {
ObjectKey = object_key
});
if (reply.ObjectExists)
{
result = reply.Object.Val;
got_result = true;
}
// server is crashed
} catch
{
handle_crashed_server(attached_server_id);
got_result = false;
}
}
}
if (got_result == false)
{
result = "N/A";
}
Console.WriteLine("Read Result: " + result);
}
public void lockReplicas(Dictionary <string, ServerCommunicationService.ServerCommunicationServiceClient> replicas, DataStoreKeyDto key)
{
foreach (string replica_id in replicas.Keys)
{
try
{
replicas[replica_id].LockObject(new lockRequest
{
PartitionId = key.PartitionId,
ObjectId = key.ObjectId
});
}
catch (Exception)
{
Console.WriteLine("Replica cannot be reached: " + replica_id);
replicas.Remove(replica_id);
}
}
}