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From Robert Newson <rnew...@apache.org>
Subject Re: Views with include_docs=true including old or incomplete results.
Date Thu, 31 Oct 2013 13:39:05 GMT
https://wiki.apache.org/couchdb/HTTP_view_API

The include_docs option will include the associated document. However,
the user should keep in mind that there is a race condition when using
this option. It is possible that between reading the view data and
fetching the corresponding document that the document has changed. If
you want to alleviate such concerns you should emit an object with a
_rev attribute as in emit(key, {"_rev": doc._rev}). This alleviates
the race condition but leaves the possibility that the returned
document has been deleted (in which case, it includes the "_deleted":
true attribute). Note: include_docs will cause a single document
lookup per returned view result row. This adds significant strain on
the storage system if you are under high load or return a lot of rows
per request. If you are concerned about this, you can emit the full
doc in each row; this will increase view index time and space
requirements, but will make view reads optimally fast.

B.


On 31 October 2013 13:09, Mclean, Adam <adam.mclean@rbc.com> wrote:
> I have a busy database that I'm querying with a view like "_design/[doc]/_view/[view]?include_docs=true"
>
> I'm having trouble with old or incomplete documents being included in the result.
>
> I see that either:
> a) include_docs is including the previous version of the document - a version of the
document that wouldn't actually match the view.
> b) include_docs is not including the document.  It includes the 'key', and 'value', but
the 'doc' is empty in output.
>
> This only occurs if I'm querying the view at roughly the same time (within a few ms)
of the incorrectly included document being written.  The document being written/updated DOES
match the view criteria, however the include_docs seems to have a timing issue where it retrieves
an old copy of the document, or doesn't include anything in the "doc": {} portion of the result.
>
> So in summary I think the view logic is fine, but include_docs seems to retrieve incorrect
documents when the timing lines up.
>
> I'm using CouchDB 1.3.1 with ERL R15B02 and Spidermonkey 1.8.5 on Linux.
>
> Is this a caveat of using include_docs?  Would I be smarter to get the keys, then make
a second query to couch to get the documents?  Was this something 'known' in 1.3.1 and fixed
in 1.4?
>
> Thanks!
>
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