<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div>Another piece of information that would be good to know is: what are the persistency requirements?</div><div><br></div><div>Is there a need for state to survive system crashes/restarts? Is there a need for redundancy at all?</div><div><br></div><div>If there is no need for persistency, Erlang has a wonderful model for holding FSM state - a process per FSM. Keeping tens of thousand processes in one erlang node is no problem whatsoever.</div><div><br></div><div>Keeping track of tens of thousand live processes used to be a problem, but that was why gproc was created, and it works very well as a process "index".</div><div><br></div><div>Various requirements on fault tolerance may make this model impractical. Speed or data volume requirements* may also drive towards a different solution, quite often in conflicting ways, so as Joe says, it's important to be specific - also about which tradeoffs are acceptable.</div><div><br></div><div>BR,</div><div>Ulf W</div><div><br></div><br><div><div>On 2 May 2011, at 09:52, Joe Armstrong wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">You haven't sent enough information to make a reasonable judgment.<br><br>what is "lots" in the phrase "lots of state transactions per transaction" - 10? 1000? 10^10<br>what is "high" in "extremely high"<br>
<br>You need to quantity words like "lots" and "high" with numbers or ranges of numbers <br><br>How many transactions/second?<br>How many simultaneous sessions?<br>How large is the state<br>Do you want the fault-tolerance?<br>
What are the latency requirements<br>Up-time requirements<br><br>and so on.<br><br>Sounds to me like you want a fault-tolerant low-latency key-value store.<br><br>CouchDb will store all the data forever, which is probably not what you want. Scalaris or Riak <br>
sounds like a better fit.<br><br>/Joe<br><br><br><div class="gmail_quote">On Mon, May 2, 2011 at 8:56 AM, David Mitchell <span dir="ltr"><<a href="mailto:monch1962@gmail.com">monch1962@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">Hi all,<div><br></div><div>I've got to build an enormous finite state machine (FSM) to hold state for tens of thousands of in-flight transactions. The various state transitions aren't well known yet; all I know is there's going to be lots of state transactions per transaction, transaction volume will be extremely high, and I'll probably have a bare minimum of time to throw together a working solution ;-></div>
<div><br></div><div>In the past I've used mnesia to hold transaction state for similar projects, but I've read a few articles about problems with it scaling and have a bit of a concern on that count for this particular project. I've been using CouchDB for a few unrelated projects recently, and have been impressed with it on every score - on the surface it seems to be a good fit for my specific problem. However I haven't stumbled on anybody using CouchDB as a high throughput, transitional data store - everything I've read about it has involved CouchDB working more or less as a NoSQL version of a "traditional" write-once, read-often data store.</div>
<div><br></div><div>My application is far more "write-once, update-many-times-very-quickly, delete" from a data perspective.</div><div><br></div><div>Has anyone used CouchDB as a FSM data store in a similar project in the past? Pros and cons? Any tips or suggestions?</div>
<div><br></div><div>Thanks in advance</div><div><br></div><font color="#888888"><div>David Mitchell</div>
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<span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><div>Ulf Wiger, CTO, Erlang Solutions, Ltd.</div><div><a href="http://erlang-solutions.com">http://erlang-solutions.com</a></div><div><br></div></span><br class="Apple-interchange-newline">
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