Using:
StackExchange.Redis v1.1.608.0
RedLock.net v1.7.4.0
This code always returns false after 250-600ms:
var eps = new [] { new DnsEndPoint("localhost", 6379) };
var lf = new RedisLockFactory(eps);
var resource = "the-thing-we-are-locking-on";
var expiry = TimeSpan.FromSeconds(30);
using (var redisLock = lf.Create(resource, expiry))
{
Response.Write("Lock acquired: " + redisLock.IsAcquired);
}
I'm struggling to work out why, as I'm able to cache things in Redis just fine with StackExchange.Redis connection string localhost,allowAdmin=true.
In the Redis console I can see a client is being connected, but that's as far as it gets.
I've added a firewall rule for port 6379 but nothing changed.
Any ideas on my the lock can never be acquired?
Found the cause of the issue. I'm using MSOpenTech Redis server v3.2.100:
https://github.com/MSOpenTech/redis/releases
Rolling back to v3.0.500 appears to fix the issue. Not ideal, but in testing environment should be OK for now.
Related
I'm trying to use the following Lua script using C# StackExchange library:
private const string LuaScriptToExecute = #"
local current
current = redis.call(""incr"", KEYS[1])
if current == 1 then
redis.call(""expire"", KEYS[1], KEYS[2])
return 1
else
return current
end
Whenever i'm evaluating the script "as a string", it works properly:
var incrementValue = await Database.ScriptEvaluateAsync(LuaScriptToExecute,
new RedisKey[] { key, ttlInSeconds });
If I understand correctly, each time I invoke the ScriptEvaluateAsync method, the script is transmitted to the redis server which is not very effective.
To overcome this, I tried using the "prepared script" approach, by running:
_setCounterWithExpiryScript = LuaScript.Prepare(LuaScriptToExecute);
...
...
var incrementValue = await Database.ScriptEvaluateAsync(_setCounterWithExpiryScript,
new[] { key, ttlInSeconds });
Whenever I try to use this approach, I receive the following error:
ERR Error running script (call to f_7c891a96328dfc3aca83aa6fb9340674b54c4442): #user_script:3: #user_script: 3: Lua redis() command arguments must be strings or integers
What am I doing wrong?
What is the right approach in using "prepared" LuaScripts that receive dynamic parameters?
If I look in the documentation: no idea.
If I look in the unit test on github it looks really easy.
(by the way, is your ttlInSeconds really RedisKey and not RedisValue? You are accessing it thru KEYS[2] - shouldnt that be ARGV[1]? Anyway...)
It looks like you should rewrite your script to use named parameters and not arguments:
private const string LuaScriptToExecute = #"
local current
current = redis.call(""incr"", #myKey)
if current == 1 then
redis.call(""expire"", #myKey, #ttl)
return 1
else
return current
end";
// We should load scripts to whole redis cluster. Even when we dont have any.
// In that case, there will be only one EndPoint, one iteration etc...
_myScripts = _redisMultiplexer.GetEndPoints()
.Select(endpoint => _redisMultiplexer.GetServer(endpoint))
.Where(server => server != null)
.Select(server => lua.Load(server))
.ToArray();
Then just execute it with anonymous class as parameter:
for(var setCounterWithExpiryScript in _myScripts)
{
var incrementValue = await Database.ScriptEvaluateAsync(
setCounterWithExpiryScript,
new {
myKey: (RedisKey)key, // or new RedisKey(key) or idk
ttl: (RedisKey)ttlInSeconds
}
)// .ConfigureAwait(false); // ? ;-)
// when ttlInSeconds is value and not key, just dont cast it to RedisKey
/*
var incrementValue = await
Database.ScriptEvaluateAsync(
setCounterWithExpiryScript,
new {
myKey: (RedisKey)key,
ttl: ttlInSeconds
}
).ConfigureAwait(false);*/
}
Warning:
Please note that Redis is in full-stop mode when executing scripts. Your script looks super-easy (you sometimes save one trip to redis (when current != 1) so i have a feeling that this script will be counter productive in greater-then-trivial scale. Just do one or two calls from c# and dont bother with this script.
First of all, Jan's comment above is correct.
The script line that updated the key's TTL should be redis.call(""expire"", KEYS[1], ARGV[1]).
Regarding the issue itself, after searching for similar issues in RedisStackExchange's Github, I found that Lua scripts do not work really well in cluster mode.
Fortunately, it seems that "loading the scripts" isn't really necessary.
The ScriptEvaluateAsync method works properly in cluster mode and is sufficient (caching-wise).
More details can be found in the following Github issue.
So at the end, using ScriptEvaluateAsync without "preparing the script" did the job.
As a side note about Jan's comment above that this script isn't needed and can be replaced with two C# calls, it is actually quite important since this operation should be atomic as it is a "Rate limiter" pattern.
I'm trying Akka.Net Cluster Tools, in order to use the Singleton behavior and it seems to work perfectly, but just when the current singleton node "host" leaves the cluster in a gracefully way. If I suddenly shutdown the host node, the handover does not occur.
Background
I'm building a system that will be composed by four nodes (initially). One of those nodes will be the "workers coordinator" and it will be responsible to monitor some data from database and, when necessary, submit jobs to the other workers. I was thinking to subscribe to cluster events and use the role leader changing event to make an actor (on the leader node) to become a coordinator, but I think that the Cluster Singleton would be a better choice in this case.
Working sample (but just if I gracefully leave the cluster)
private void Start() {
Console.Title = "Worker";
var section = (AkkaConfigurationSection)ConfigurationManager.GetSection("akka");
var config = section.AkkaConfig;
// Create a new actor system (a container for your actors)
var system = ActorSystem.Create("SingletonActorSystem", config);
var cluster = Cluster.Get(system);
cluster.RegisterOnMemberRemoved(() => MemberRemoved(system));
var settings = new ClusterSingletonManagerSettings("processorCoordinatorInstance",
"worker", TimeSpan.FromSeconds(5), TimeSpan.FromSeconds(1));
var actor = system.ActorOf(ClusterSingletonManager.Props(
singletonProps: Props.Create<ProcessorCoordinatorActor>(),
terminationMessage: PoisonPill.Instance,
settings: settings),
name: "processorCoordinator");
string line = Console.ReadLine();
if (line == "g") { //handover works
cluster.Leave(cluster.SelfAddress);
_leaveClusterEvent.WaitOne();
system.Shutdown();
} else { //doesn't work
system.Shutdown();
}
}
private async void MemberRemoved(ActorSystem actorSystem) {
await actorSystem.Terminate();
_leaveClusterEvent.Set();
}
Configuration
akka {
suppress-json-serializer-warning = on
actor {
provider = "Akka.Cluster.ClusterActorRefProvider, Akka.Cluster"
}
remote {
helios.tcp {
port = 0
hostname = localhost
}
}
cluster {
seed-nodes = ["akka.tcp://SingletonActorSystem#127.0.0.1:4053"]
roles = [worker]
}
}
Thank you #Horusiath, your answer is totaly right! I wasn't able to find this configuration in akka.net documentation, and I didn't realize that I was supposed to take a look on the akka documentation. Thank you very much!
Have you tried to set akka.cluster.auto-down-unreachable-after to some timeout (eg. 10 sec)? – Horusiath Aug 12 at 11:27
Posting it as a response for caution for those who find this post.
Using auto-downing is NOT recommended in a clustered environment, due to different part of the system might decide after some time that the other part is down, splitting the cluster into two clusters, each with their own cluster singleton.
Related akka docs: https://doc.akka.io/docs/akka/current/split-brain-resolver.html
I'm not sure, whether it is a bug or I'm doing something wrong. Here is the code:
using StackExchange.Redis;
ConnectionMultiplexer conn = null;
while (conn == null);
{
try
{
conn = ConnectionMultiplexer.Connect("localhost:6379");
}
catch (Exception)
{
conn = null;
Thread.Sleep(TimeSpan.FromSeconds(5));
}
}
var db = conn.GetDatabase();
var transaction = db.CreateTransaction();
var tasks = new List<Task>();
tasks.Add(transaction.HashSetAsync("key", "field", "value"));
if (transaction.Execute())
{
Task.WaitAll(tasks.ToArray());
}
When I run it with started redis (windows version - 2.6, 2.8.17, 2.8.19), everything works fine. If I start redis after few loops of the cycle, either it doesn't jump into if-statement or it jumps and get blocked on WaitAll(). If I try to check values in redis, they are stored.
This situation happens when we start server and forget to start redis. After postpone start of redis it gets stuck. The same problem appears when using batch instead of transaction.
Am I doing connection to multiplexer wrong or is it bug? (I found few that looked similar but I'm not sure)
It was a bug in older versions of StackExchange.Redis - 1.0.481, 1.0.488 (didn't test any older ones). With new version 1.1.553 it works fine (https://github.com/StackExchange/StackExchange.Redis/issues/200).
I'm using autofac and the interfaces are correctly resolved but this code fails with "No connection could be made because the target machine actively refused it 127.0.0.1:8081"
using (var store = GetService<IDocumentStore>())
{
using (var session = store.OpenSession())
{
session.Store(new Entry { Author = "bob", Comment = "My son says this", EntryId = Guid.NewGuid(), EntryTime = DateTime.Now, Quote = "I hate you dad." });
session.SaveChanges();
}
}
Here is the registration
builder.Register<IDocumentStore>(c =>
{
var store = new DocumentStore { Url = "http://localhost:8081" };
store.Initialize();
return store;
}).SingleInstance();
When I navigate to http://localhost:8081 I do get the silverlight management UI. Although I'm running a Windows VM and vmware and Silverlight5 don't play together. That's another issue entirely. Anyways does anyone see what I'm doing wrong here or what I should be doing differently? Thanks for any code, tips, or tricks.
On a side note, can I enter some dummy records from a command line interface? Any docs or examples of how I can do that?
Thanks All.
Just curious, are you switching RavenDB to listen on 8081? The default is 8080. If you're getting the management studio to come up, I suspect you are.
I'm not too familiar with autofac but, it looks like you're wrapping your singleton DocumentStore in a using statement.
Try:
using (var session = GetService<IDocumentStore>().OpenSession())
{
}
As far as dummy records go, the management studio will ask you if you want to generate some dummy data if your DB is empty. If you can't get silverlight to work in the VM, I'm not sure if there's another automated way to do it.
Perhaps using smuggler:
http://ravendb.net/docs/server/administration/export-import
But you'd have to find something to import.
i am trying to setup Redis on appharbor. I have followed their instructions and again i have an issue with the Booksleeve API. Here is the code i am using to make it work initially:
var connectionUri = new Uri(url);
using (var redis = new RedisConnection(connectionUri.Host, connectionUri.Port, password: connectionUri.UserInfo.Split(new[] { ':' }, 2)[1]))
{
redis.Strings.Set(1, "greeting", "welcome to remember your stuff!");
try
{
var task = redis.Strings.GetString(1, "greeting");
redis.Wait(task);
ViewBag.Message = task.Result;
}
catch (Exception)
{
// It throws an exception trying to wait for the task?
}
}
However, the issue is that it sets the string correctly, but when trying to retrieve the same string from the key value store, it throws a timeout exception waiting for the task to eexecute. However, this code works on my local redis server connection.
Am i using the API in a wrong way? or is this something related to Appharbor?
Thanks
Like a SqlConnection, you need to call Open() (otherwise your messages are queued for delivery).
Unlike SqlConnection, you should not fire up a RedisConnection each time you need it - it is intended to be used as a shared, thread-safe, multiplexer - i.e. a single connection is held somewhere and used by lots and lots of unrelated callers. Unless of course you only need to do one thing!