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From Kevin Burton <rkevinbur...@charter.net>
Subject Re: Exist test?
Date Mon, 05 Nov 2012 19:57:36 GMT
So the update handler sets some global variable indicating that the document already exists?
How do I tell that the update handler has run to completion?

On Nov 5, 2012, at 1:50 PM, Mark Hahn <mark@hahnca.com> wrote:

> You can use an update handler.  It works with non-existent docs.  It's a
> very clean way to do it that I use.
> 
> On Mon, Nov 5, 2012 at 11:45 AM, Robert Newson <rnewson@apache.org> wrote:
> 
>> Easiest to just create the document, you'll get a 409 response to indicate
>> that it already existed. If your documents don't have user assigned id's,
>> then I don't see how you could check for existence before writing anyway.
>> 
>> 
>> On 5 November 2012 19:40, Kevin Burton <rkevinburton@charter.net> wrote:
>> 
>>> I am mainly using it the context of initially populating a database. So
>>> there isn't any danger of a race because there is only one user.
>>> 
>>> On Nov 5, 2012, at 12:47 PM, Jens Alfke <jens@couchbase.com> wrote:
>>> 
>>>> 
>>>> On Nov 5, 2012, at 10:22 AM, Kevin Burton <rkevinburton@charter.net>
>>> wrote:
>>>> 
>>>>> I am calling CreateDocument<Document>() but I suspect that testing
if
>>> the document exists first may perform better in the long run. I am using
>>> DreamSeat for my driver but I suspect other drivers have a similar
>> "test".
>>> My problem is that I don't know what to test for and I am unfamiliar with
>>> the available methods. Any one successfully use such a pattern
>> (preferably
>>> with DreamSeat) that tests for existence then creates if the document
>>> doesn't exist? Keep in mind I don't initially have an id. Thank you.
>>>> 
>>>> I don’t know anything about that particular API, but in general,
>>> check-then-create doesn’t work well in a concurrent environment. It’s
>> prone
>>> to race conditions where something else creates the resource in between
>>> your check call and your create call. (The canonical example is checking
>>> whether a file exists, then creating the file, which is a classic old
>>> security hole in privileged Unix tools.)
>>>> 
>>>> —Jens
>> 

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