Am I misunderstand read and write quorum? Or am I losing writes?

Christian Dahlqvist christian at basho.com
Fri Apr 12 05:13:49 EDT 2013


Hi Rob,

If you print the fields in the document you retrieved from Riak, does it appear to be an older version? Could there perhaps be some problem with serialisation/de-serialisation of the data?

Regards,

Christian 



On 12 Apr 2013, at 07:30, Erik Søe Sørensen <ess at trifork.com> wrote:

> Is there any chance that the key in question exists in the bucket prior to the test? If so, then you should update the value (read+write) instead of trying to create it as a whole new object. This has to do with the nature of vector clocks.
> 
> /Erik [not familiar with the Python client API]
> 
> 
> 
> -------- Oprindelig meddelelse --------
> Fra: Rob Speer <rob at luminoso.com>
> Dato:
> Til: riak-users Users <riak-users at lists.basho.com>
> Emne: Am I misunderstand read and write quorum? Or am I losing writes?
> 
> 
> My understanding is that if you write a document to a cluster of 4 riak servers with w='quorum', then read from that same cluster with r='quorum', that the read should reflect the result of the right.
> 
> My understanding is also that, in the Python client (version 5525f4f3, from master), w = r = 'quorum' by default.
> 
> And yet, the following check in my code fails occasionally:
> 
> riak_obj = bucket.new(docid, doc)
> riak_obj.store()
> echo_doc = bucket.get(docid).data
> for field in doc:
>    assert doc[field] == echo_doc[field], (doc, echo_doc)
> 
> 
> I thought perhaps my W and R settings were wrong and I was just getting "eventual consistency", so I tried a very slow version where I waited five seconds before reading the updated document. This seems to fail just as often. So it doesn't just seem like I'm reading a write that hasn't happened yet; it seems that the occasional write may _never happen at all_.
> 
> Have I misunderstood something? If not, why would this happen, and how can I track it down?
> -- Rob
> 
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> riak-users at lists.basho.com
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