On Nov 1, 2009, at 4:29 PM, Brian Candler wrote:
On Fri, Oct 30, 2009 at 06:46:24AM -0400, Damien Katz wrote:
* Application writer curses couchdb, and curses the person who wrote
"Most applications require no special planning to take advantage of
distributed updates and replication".
It sounds like the dev didn't read the documentation.
I believe the documentation is weak in this area, but I am
attempting to
improve it.
I think it's fair to say that the first documentation anyone reads
about
CouchDB screams out: "RESTful HTTP API". Most people associate
"REST" with
GET and PUT. This in turn leads them down the path of writing apps
which use
PUT, and handling conflicts by trapping 409 responses and retrying
at write
time.
It works at first, but this approach will not serve them when they
get to
distributed updates and replication. At very least, they'll need
another
layer of conflict resolution, and that could involve substantial
application
changes.
With some "special planning" they could have decided to use the
somewhat
obscure POST-to-_bulk_docs-with-all_or_nothing-true instead of PUT,
and
implemented conflict resolution just once in a way which *does* also
work
with distributed updates and replication.
I'm guessing you are taking some issue with the wording off this on
the website. "Most applications require no special planning to take
advantage of distributed updates and replication." from here: http://couchdb.apache.org/docs/intro.html
For apps that are document oriented, I think this claim is true. I
suppose we could say "many" instead of "most" for less controversial
wording.
However, for "many" apps there is no need for special planning, it's
enough to present the conflicting docs to the user with simple diffing
tools. This detection and handling is can be added after the app is
built and is sufficient for many common use cases.
Patches are welcome, and most everything you propose could be done in
front end that's not that involved.
Some of it can be done in a front-end.
Reviewing my own code, most often I retrieve documents by using a
multi-key
fetch against a view (either _all_docs or a user view). Writing a
front-end
to that which also gives you the information needed to resolve
conflicts is
hard - I think you'd end up having to GET each document
individually, which
rather defeats the object of include_docs=true. I've raised that as
COUCHDB-549.
Thanks.
Regards,
Brian.
