Java Riak client can't handle a Riak node failure?

Dmitri Zagidulin dzagidulin at basho.com
Wed Oct 7 16:02:00 EDT 2015


Glad you sorted it out!

(I do want to encourage you to bump your R setting to at least 2, though.
Run some tests -- I think you'll find that the difference in speed will not
be noticeable, but you do get a lot more data resilience with 2.)

On Wed, Oct 7, 2015 at 6:24 PM, Vanessa Williams <
vanessa.williams at thoughtwire.ca> wrote:

> Hi Dmitri, well...we solved our problem to our satisfaction but it turned
> out to be something unexpected.
>
> The keys were two properties mentioned in a blog post on "configuring
> Riak’s oft-subtle behavioral characteristics":
> http://basho.com/posts/technical/riaks-config-behaviors-part-4/
>
> notfound_ok= false
> basic_quorum=true
>
> The 2nd one just makes things a little faster, but the first one is the
> one whose default value of true was killing us.
>
> With r=1 and notfound_ok=true (default) the first node to respond, if it
> didn't find the requested key, the authoritative answer was "this key is
> not found". Not what we were expecting at all.
>
> With the changed settings, it will wait for a quorum of responses and only
> if *no one* finds the key will "not found" be returned. Perfect. (Without
> this setting it would wait for all responses, not ideal.)
>
> Now there is only one snag, which is that if the Riak node the client
> connects to goes down, there will be no communication and we have a
> problem. This is easily solvable with a load-balancer, though for
> complicated reasons we actually don't need to do that right now. It's just
> acceptable for us temporarily. Later, we'll get the load-balancer working
> and even that won't be a problem.
>
> I *think* we're ok now. Thanks for your help!
>
> Regards,
> Vanessa
>
>
>
> On Wed, Oct 7, 2015 at 9:33 AM, Dmitri Zagidulin <dzagidulin at basho.com>
> wrote:
>
>> Yeah, definitely find out what the sysadmin's experience was, with the
>> load balancer. It could have just been a wrong configuration or something.
>>
>> And yes, that's the documentation page I recommend -
>> http://docs.basho.com/riak/latest/ops/advanced/configs/load-balancing-proxy/
>> Just set up HAProxy, and point your Java clients to its IP.
>>
>> The drawbacks to load-balancing on the java client side (yes, the cluster
>> object) instead of a standalone load balancer like HAProxy, are the
>> following:
>>
>> 1) Adding node means code changes (or at very least, config file changes)
>> rolled out to all your clients. Which turns out to be a pretty serious
>> hassle. Instead, HAProxy allows you to add or remove nodes without changing
>> any java code or config files.
>>
>> 2) Performance. We've ran many tests to compare performance, and
>> client-side load balancing results in significantly lower throughput than
>> you'd have using haproxy (or nginx). (Specifically, you actually want to
>> use the 'leastconn' load balancing algorithm with HAProxy, instead of round
>> robin).
>>
>> 3) The health check on the client side (so that the java load balancer
>> can tell when a remote node is down) is much less intelligent than a
>> dedicated load balancer would provide. With something like HAProxy, you
>> should be able to take down nodes with no ill effects for the client code.
>>
>> Now, if you load balance on the client side and you take a node down,
>> it's not supposed to stop working completely. (I'm not sure why it's
>> failing for you, we can investigate, but it'll be easier to just use a load
>> balancer). It should throw an error or two, but then start working again
>> (on the retry).
>>
>> Dmitri
>>
>> On Wed, Oct 7, 2015 at 2:45 PM, Vanessa Williams <
>> vanessa.williams at thoughtwire.ca> wrote:
>>
>>> Hi Dmitri, thanks for the quick reply.
>>>
>>> It was actually our sysadmin who tried the load balancer approach and
>>> had no success, late last evening. However I haven't discussed the gory
>>> details with him yet. The failure he saw was at the application level (i.e.
>>> failure to read a key), but I don't know a) how he set up the LB or b) what
>>> the Java exception was, if any. I'll find that out in an hour or two and
>>> report back.
>>>
>>> I did find this article just now:
>>>
>>>
>>> http://docs.basho.com/riak/latest/ops/advanced/configs/load-balancing-proxy/
>>>
>>> So I suppose we'll give those suggestions a try this morning.
>>>
>>> What is the drawback to having the client connect to all 4 nodes (the
>>> cluster client, I assume you mean?) My understanding from reading articles
>>> I've found is that one of the nodes going away causes that client to fail
>>> as well. Is that what you mean, or are there other drawbacks as well?
>>>
>>> If there's anything else you can recommend, or links other than the one
>>> above you can point me to, it would be much appreciated. We expect both
>>> node failure and deliberate node removal for upgrade, repair, replacement,
>>> etc.
>>>
>>> Regards,
>>> Vanessa
>>>
>>> On Wed, Oct 7, 2015 at 8:29 AM, Dmitri Zagidulin <dzagidulin at basho.com>
>>> wrote:
>>>
>>>> Hi Vanessa,
>>>>
>>>> Riak is definitely meant to run behind a load balancer. (Or, at the
>>>> worst case, to be load-balanced on the client side. That is, all clients
>>>> connect to all 4 nodes).
>>>>
>>>> When you say "we did try putting all 4 Riak nodes behind a
>>>> load-balancer and pointing the clients at it, but it didn't help." -- what
>>>> do you mean exactly, by "it didn't help"? What happened when you tried
>>>> using the load balancer?
>>>>
>>>>
>>>>
>>>> On Wed, Oct 7, 2015 at 1:57 PM, Vanessa Williams <
>>>> vanessa.williams at thoughtwire.ca> wrote:
>>>>
>>>>> Hi all, we are still (for a while longer) using Riak 1.4 and the
>>>>> matching Java client. The client(s) connect to one node in the cluster
>>>>> (since that's all it can do in this client version). The cluster itself has
>>>>> 4 nodes (sorry, we can't use 5 in this scenario). There are 2 separate
>>>>> clients.
>>>>>
>>>>> We've tried both n_val = 3 and n_val=4. We achieve
>>>>> consistency-by-writes by setting w=all. Therefore, we only require one
>>>>> successful read (r=1).
>>>>>
>>>>> When all nodes are up, everything is fine. If one node fails, the
>>>>> clients can no longer read any keys at all. There's an exception like this:
>>>>>
>>>>> com.basho.riak.client.RiakRetryFailedException:
>>>>> java.net.ConnectException: Connection refused
>>>>>
>>>>> Now, it isn't possible that Riak can't operate when one node fails, so
>>>>> we're clearly missing something here.
>>>>>
>>>>> Note: we did try putting all 4 Riak nodes behind a load-balancer and
>>>>> pointing the clients at it, but it didn't help.
>>>>>
>>>>> Riak is a high-availability key-value store, so... why are we failing
>>>>> to achieve high-availability? Any suggestions greatly appreciated, and if
>>>>> more info is required I'll do my best to provide it.
>>>>>
>>>>> Thanks in advance,
>>>>> Vanessa
>>>>>
>>>>> --
>>>>> Vanessa Williams
>>>>> ThoughtWire Corporation
>>>>> http://www.thoughtwire.com
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> riak-users mailing list
>>>>> riak-users at lists.basho.com
>>>>> http://lists.basho.com/mailman/listinfo/riak-users_lists.basho.com
>>>>>
>>>>>
>>>>
>>>
>>
>
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