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From Matt Goodall <matt.good...@gmail.com>
Subject Re: Deleted docs can be accidentally resurrected
Date Fri, 20 Nov 2009 00:03:23 GMT
2009/11/19 Adam Kocoloski <kocolosk@apache.org>:
> On Nov 18, 2009, at 6:51 PM, Matt Goodall wrote:
>
>> 2009/11/18 Sebastian Cohnen <sebastiancohnen@googlemail.com>:
>>> afaik, this behavior is normal. you just created another (and new) resource/document.
>>>
>>> have a look (the database test is new and never contained docs with id 'foo'
or 'foobar'):
>>>
>>> $ curl -X PUT -d '{"_id": "foo", "_rev": "1-967a00dff5e02add41819138abb3284d",
"num": 1}' "http://localhost:5984/test/foo"
>>> {"ok":true,"id":"foo","rev":"2-65371ad05fc99a9b794f68c6003bc8da"}
>>>
>>> $ curl -X PUT -d '{"_id": "foobar", "_rev": "4-anythingyouwant", "num": 1}' "http://localhost:5984/test/foobar"
>>> {"ok":true,"id":"foobar","rev":"5-084106c9189a346875996e76c1833630"}
>>
>> Hmm, seems wrong to me although I can imagine that's useful during
>> replication (which doesn't mean it should work for a PUT). However,
>> why does the following fail then:
>>
>> $ curl -X "PUT" -d '{}' "http://localhost:15984/test/foo"
>> {"ok":true,"id":"foo","rev":"1-967a00dff5e02add41819138abb3284d"}
>> $ curl -X "PUT" -d '{"_id": "foo", "_rev":
>> "1-967a00dff5e02add41819138abb3284d"}'
>> "http://localhost:15984/test/foo"
>> {"ok":true,"id":"foo","rev":"2-7051cbe5c8faecd085a3fa619e6e6337"}
>> $ curl -X "DELETE"
>> "http://localhost:15984/test/foo?rev=2-7051cbe5c8faecd085a3fa619e6e6337"
>> {"ok":true,"id":"foo","rev":"3-7379b9e515b161226c6559d90c4dc49f"}
>> $ curl -X "PUT" -d '{"_id": "foo", "_rev":
>> "1-967a00dff5e02add41819138abb3284d"}'
>> "http://localhost:15984/test/foo"
>> {"error":"conflict","reason":"Document update conflict."}
>>
>> - Matt
>>
>>>
>>>
>>> cheers,
>>>
>>> tisba / Sebastian
>>>
>>> On 18.11.2009, at 23:56, Matt Goodall wrote:
>>>
>>>> Hi,
>>>>
>>>> I swear I've reported this odd behaviour before but I can't find any
>>>> mention of it now ...
>>>>
>>>> I have some code with a race condition that is caused by what I
>>>> believe is a bug in CouchDB - a deleted document can be updated using
>>>> an old, valid rev.
>>>>
>>>> If a document has not been deleted then CouchDB correctly returns a
>>>> conflict error if the latest rev is not sent. However, once deleted,
>>>> any rev in the docs history can be sent as the update and, as long as
>>>> the doc is changed in some way, the document will be resurrected with
>>>> a rev whose sequence is 1 more than that sent in the update.
>>>>
>>>> Create new doc ...
>>>> $ curl -X "PUT" -d '{"_id": "foo"}' http://localhost:15984/test/foo
>>>> {"ok":true,"id":"foo","rev":"1-967a00dff5e02add41819138abb3284d"}
>>>>
>>>> Update a couple of times to move the rev on ...
>>>> $ curl -X "PUT" -d '{"_id": "foo", "_rev":
>>>> "1-967a00dff5e02add41819138abb3284d"}' http://localhost:15984/test/foo
>>>> {"ok":true,"id":"foo","rev":"2-7051cbe5c8faecd085a3fa619e6e6337"}
>>>> $ curl -X "PUT" -d '{"_id": "foo", "_rev":
>>>> "2-7051cbe5c8faecd085a3fa619e6e6337"}' http://localhost:15984/test/foo
>>>> {"ok":true,"id":"foo","rev":"3-825cb35de44c433bfb2df415563a19de"}
>>>>
>>>> Delete the doc ...
>>>> $ curl -X "DELETE"
>>>> "http://localhost:15984/test/foo?rev=3-825cb35de44c433bfb2df415563a19de"{"ok":true,"id":"foo","rev":"4-1df13287548620bf858cf9d1b810972a"}
>>>>
>>>> Update using an old rev, changing something ...
>>>> $ curl -X "PUT" -d '{"_id": "foo", "_rev":
>>>> "1-967a00dff5e02add41819138abb3284d", "num": 1}'
>>>> http://localhost:15984/test/foo
>>>> {"ok":true,"id":"foo","rev":"2-65371ad05fc99a9b794f68c6003bc8da"}
>>>>
>>>> Now, I can sort of understand how something like that might happen
>>>> during replication but there's no replication going on here and
>>>> there's no conflict created in the database.
>>>>
>>>> I can't think of a way around the problem at the moment, other than
>>>> marking the document for deletion and then sweeping it later when
>>>> something else is hopefully not going to be touching the document.
>>>> But, frankly, that's horrible,
>>>>
>>>> - Matt
>
> Hi Matt, bizarre.  Your latest email shows the behavior I expect -- you tried to PUT
a document using an incorrect MVCC revision, and you got a conflict as a result.  A successful
PUT of a new document with an _id that corresponds to a previously deleted document should
omit the MVCC rev.

Yep, I only posted that (it's what I would expect too) to demonstrate
how weird the problem is.

>
> Your first email is the weird one -- you supplied an old MVCC _rev, but changed the body
to something different than the body at the time the doc was deleted, and it worked.  I can
confirm this.  Can you file a JIRA ticket?  Best,

Exactly. If there's a rev then it should match the current rev of the
doc or fail.

I'll file a ticket tomorrow morning.

Thanks.

- Matt

>
> Adam

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