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From Pepijn de Vos <pepijnde...@yahoo.com>
Subject Re: [proposal] Update Handler Conflict Resolution
Date Sun, 11 Sep 2011 08:28:14 GMT
Yes, I would imagine the update function tries to commit the result. Maybe update could itself
return the new document?

I think rnewson or jan____ said there was already some sort of timeout in place.

Pepijn

On Sep 11, 2011, at 4:54 AM, Randall Leeds wrote:

> On Fri, Sep 9, 2011 at 06:37, Pepijn de Vos <pepijndevos@yahoo.com> wrote:
> 
>> Hi,
>> 
>> Today I had a long and complicated discussion involving rnewson, jan____,
>> me and muhqu.
>> 
>> I was falsely assuming Document Update Handlers did atomic updates. Truth
>> is that they don't, but for most of my use cases could.
>> 
>> What currently happens is that the update handler gets executed with the
>> latest rev of the requested doc. When the update is completed, it is
>> committed, but when another update has meanwhile happened, a conflict arises
>> and 409 is returned.
>> 
>> When I use update handlers, I mostly use idempotent functions. This means
>> that it is safe for the update handler to retry on its own account, and in
>> doing so, avoid a ton of latency and headaches.
>> 
>> Only, it turns out that programmatic updates are not the sole use for
>> update handlers, so rnewson argued that it might destroy data.
>> 
>> Proposal 1:
>> Add an idempotent=true parameter to the handler, allowing it to retry on
>> its own.
>> 
>> Proposal 2:
>> Add an update() function so the handler can handle conflicts in itself.
>> 
> 
> Just so I understand... is update() a function called from within the
> handler that tries to commit the result?
> If this fails, should there be a function to retrieve the latest version of
> the document again?
> I sort of like this approach. Proposal 1 makes some sense but I worry about
> a request potentially being retried 'forever' and not sure how to impose
> limits on that without expanding our configuration space or HTTP API surface
> area when proposal 2 is perhaps cleaner.
> 
> -Randall


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