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https://issues.apache.org/jira/browse/COUCHDB-1256?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13088952#comment-13088952
]
Adam Kocoloski commented on COUCHDB-1256:
-----------------------------------------
Hi Filipe, it is definitely not the case that "if the replicator checkpointed
sequence 2, it means it received and processed revision
1-0dc33db52a43872b6f3371cef7de0277 of foo". Please take a closer look at the
full _changes response in the initial report:
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}
Revision 1-0dc33d of "foo" shows up in sequence 3, which is after sequence 2.
The replicator should checkpoint sequence 2 iff it has replicated all the
entries in the _changes feed up to and including sequence 2. Once again, that
does not include 1-0dc33d. If I resume the replication from a checkpoint at
sequence 2 I will not receive 1-0dc33d.
> 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
> Affects Versions: 0.10, 0.10.1, 0.10.2, 0.11.1, 0.11.2, 1.0, 1.0.1, 1.0.2,
> 1.1, 1.0.3
> 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
>
> Attachments: jira-1256-test.diff
>
>
> 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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