Hey Alexander, thanks for the response. Yup - I'm a Riak newbie for sure :). I have replication set to 3 on the cluster. So, if dw=2, is it durable or not? even if it's durable across vnodes. If it is durable across vnodes, then it should be queryable?
One of the big considerations I have to look into is if the client writes to the server, and that client gets told that the key has been written, is it actually on disk or not? Eventual consistency is fine, but many of the other datastores have a WAL (much like leveldb), so at least if I pull the plug or the app dies we know that on restart the key is actually available. Do any of the RIAK settings give me this? (I thought that I was getting this with dw=2/r=2/w=2 and replication). Lazy writing of the data is not really an option for what we need. thanks again, Pat Subject: Re: missing keys? From: sicul...@gmail.com Date: Fri, 14 Sep 2012 12:51:28 -0400 CC: rzeze...@basho.com; riak-users@lists.basho.com To: plynch1...@hotmail.com Hi Pat, "thanks for that. Is the default on dw not also quorum though?? so, in my case it should be 2 (since I have 2 nodes)??" Consider the difference in the usage of the word "node." There is actually a large difference between two definitions of the commonly used word, "node." 1. node: virtual node, as indicated by the ring_creation_size default value, which is 64, and can be changed in app.config. 2. node: physical node, which is the number of physical machines in a cluster. Historically and at the moment, virtual nodes are evenly divided amongst physical nodes. The term "node" has been conflated and continues to be a pain point for newcomers to Riak (not that you are a newcomer, but in general). In all cases, the values r, w, dw and considerations for quorum are entirely dependent on the replication value, known as n or n_val, which in turn represents replicas on a per virtual node basis. Hope that clears some stuff up, -Alexander Sicular @siculars On Sep 14, 2012, at 12:17 PM, Pat Lynch wrote:Hi, thanks for that. Is the default on dw not also quorum though?? so, in my case it should be 2 (since I have 2 nodes)?? thanks, Pat. Date: Fri, 14 Sep 2012 12:11:25 -0400 Subject: Re: missing keys? From: rzeze...@basho.com To: plynch1...@hotmail.com CC: s...@basho.com; riak-users@lists.basho.com Pat, On Fri, Sep 14, 2012 at 11:08 AM, Pat Lynch <plynch1...@hotmail.com> wrote: So, if I write a key to a cluster and then try to query that key, it may not find it unless I retry? Even if r=2 & w=2 ? I thought that at least 2 systems had to have that key (either in memory or disk) for the write to have succeeded with those settings? If I had w=3, would you expect any missed keys ?? (note that I didn't try that because I expected performance issues). It's important to note that `w` is considered complete once the value is queued in-memory waiting to be written do disk [1]. A read does not check the queue but only on-disk data. The `dw` flag is what you want to know that the value has made it to disk and can be seen by a read. -Z [1]: https://github.com/basho/riak_kv/blob/master/src/riak_kv_vnode.erl#L284_______________________________________________ riak-users mailing list riak-users@lists.basho.com http://lists.basho.com/mailman/listinfo/riak-users_lists.basho.com
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