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Date: Mon, 22 Aug 2011 14:20:29 +0000 (UTC)
From: "Adam Kocoloski (JIRA)" <jira@apache.org>
To: dev@couchdb.apache.org
Message-ID: 
 <1136929143.1164.1314022829540.JavaMail.tomcat@hel.zones.apache.org>
Subject: [jira] [Created] (COUCHDB-1256) Incremental requests to _changes
 can skip revisions
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Incremental requests to _changes can skip revisions
---------------------------------------------------

                 Key: COUCHDB-1256
                 URL: https://issues.apache.org/jira/browse/COUCHDB-1256
             Project: CouchDB
          Issue Type: Bug
          Components: Replication
         Environment: confirmed on Apache CouchDB 1.1.0, bug appears to be present in 1.0.3 and trunk
            Reporter: Adam Kocoloski
            Assignee: Adam Kocoloski
            Priority: Blocker
             Fix For: 1.0.4, 1.1.1, 1.2


Requests to _changes with style=all_docs&since=N (requests made by the replicator) are liable to suppress revisions of a document.  The following sequence of curl commands demonstrates the bug:

curl -X PUT localhost:5985/revseq 
{"ok":true}

curl -X PUT -Hcontent-type:application/json localhost:5985/revseq/foo -d '{"a":123}'
{"ok":true,"id":"foo","rev":"1-0dc33db52a43872b6f3371cef7de0277"}

curl -X PUT -Hcontent-type:application/json localhost:5985/revseq/bar -d '{"a":456}'
{"ok":true,"id":"bar","rev":"1-cc609831f0ca66e8cd3d4c1e0d98108a"}

% stick a conflict revision in foo
curl -X PUT -Hcontent-type:application/json localhost:5985/revseq/foo?new_edits=false -d '{"_rev":"1-cc609831f0ca66e8cd3d4c1e0d98108a", "a":123}'
{"ok":true,"id":"foo","rev":"1-cc609831f0ca66e8cd3d4c1e0d98108a"}

% request without since= gives the expected result
curl -Hcontent-type:application/json localhost:5985/revseq/_changes?style=all_docs
{"results":[
{"seq":2,"id":"bar","changes":[{"rev":"1-cc609831f0ca66e8cd3d4c1e0d98108a"}]},
{"seq":3,"id":"foo","changes":[{"rev":"1-cc609831f0ca66e8cd3d4c1e0d98108a"},{"rev":"1-0dc33db52a43872b6f3371cef7de0277"}]}
],
"last_seq":3}

% request starting from since=2 suppresses revision 1-0dc33db52a43872b6f3371cef7de0277 of foo
macbook:~ (master) $ curl localhost:5985/revseq/_changes?style=all_docs\&since=2
{"results":[
{"seq":3,"id":"foo","changes":[{"rev":"1-cc609831f0ca66e8cd3d4c1e0d98108a"}]}
],
"last_seq":3}

I believe the fix is something like this (though we could refactor further because Style is unused):

diff --git a/src/couchdb/couch_db.erl b/src/couchdb/couch_db.erl
index e8705be..65aeca3 100644
--- a/src/couchdb/couch_db.erl
+++ b/src/couchdb/couch_db.erl
@@ -1029,19 +1029,7 @@ changes_since(Db, Style, StartSeq, Fun, Acc) ->
     changes_since(Db, Style, StartSeq, Fun, [], Acc).
     
 changes_since(Db, Style, StartSeq, Fun, Options, Acc) ->
-    Wrapper = fun(DocInfo, _Offset, Acc2) ->
-            #doc_info{revs=Revs} = DocInfo,
-            DocInfo2 =
-            case Style of
-            main_only ->
-                DocInfo;
-            all_docs ->
-                % remove revs before the seq
-                DocInfo#doc_info{revs=[RevInfo ||
-                    #rev_info{seq=RevSeq}=RevInfo <- Revs, StartSeq < RevSeq]}
-            end,
-            Fun(DocInfo2, Acc2)
-        end,
+    Wrapper = fun(DocInfo, _Offset, Acc2) -> Fun(DocInfo, Acc2) end,
     {ok, _LastReduction, AccOut} = couch_btree:fold(by_seq_btree(Db),
         Wrapper, Acc, [{start_key, StartSeq + 1}] ++ Options),
     {ok, AccOut}.


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