Inconsistent errors on repeated replace() followed by remove() on the same key

Performing a REPLACE_WITH_CAS operation on a key which has recently been deleted and then requested can occasionally return KEY_EEXISTS (key exists but with different CAS) instead of the expected KEY_ENOENT.

Steps to reproduce

Repeatedly:

1. Create document
2. Delete document
3. Attempt to fetch document
4. Attempt to replace document, specifying a CAS

#!/usr/bin/env python                                                                                                                                                                                                                                                                                                                                   

from couchbase.bucket import Bucket

from couchbase.exceptions import NotFoundError

client = Bucket('couchbase://127.0.0.1:12000/default')

while True:

    client.set("key", "x")

    client.delete("key")

    try:

        client.get("key")

        assert False

    except (NotFoundError):

        pass

    try:

        client.replace("key", "value", cas=10)

    except (NotFoundError):

        pass

As an aside, the code here is basically making incorrect assumptions about the possible return values when using replace with CAS and not handling KEY_EEXISTS :-

• If you're in a single-client environment then the CAS is pointless (there's no possible concurrency), and so the REPLACE would always return KEY_ENOENT
• If you're in a multi-client environment (and hence using CAS to replace a given specific version of a document) then you need to handle both KEY_EEXISTS and KEY_ENOENT as:
  1. KEY_EEXISTS could be returned if another client modified the document (and hence the CAS has changed).
  2. KEY_ENOENT could be returned if another client has deleted the document.

As such I'm setting this as `minor` priority and targeting Spock.