Paul, Love your work mate! Outstanding commit msg, I'm working through it (slowly).
A+ D On 2 September 2011 16:31, <[email protected]> wrote: > Author: davisp > Date: Fri Sep 2 04:31:10 2011 > New Revision: 1164350 > > URL: http://svn.apache.org/viewvc?rev=1164350&view=rev > Log: > Fix introduction of duplicates into _changes feed > > When a document is updated the new update_seq is assigned as part of the > rev_tree merging in couch_db_updater:merge_rev_trees/7 based on the > condition of whether the new rev_tree is equal to the old tree. This > equality is done as a simple Erlang term comparison. If the trees are > not equal a new update_seq is assigned to the #full_doc_info{} record > that is stored in fulldocinfo_by_id_btree. > > During replication it is possible that a document update merges into the > rev_tree internally without creating a leaf. If the terminal node of the > replicated path happens to land on a node with a value of ?REV_MISSING > the new document information will be preferred and replace the > ?REV_MISSING value. > > This preference ends up causing the rev_tree comparison to evaluate to > false which ends up giving this document a new update_seq. Up until this > point everything is fine. We write a bit of extra data (that will be > cleared during compaction) because of a previous bug where we decided to > be cautious and avoid losing data due to a broken rev_tree merging > aglorithm. It is also important to note that this is the place were we > calculate the update_seq to remove from the docinfo_by_seq_tree. > > After this point we get back to couch_db_udpater:update_docs_int/5 where > we eventually call couch_db_updater:new_index_entries/3 which creates > the new entries for the fulldocinfo_by_id_tree and docinfo_by_seq_btree. > At this point we end up creating a #doc_info{} record based on the > leaves in the rev_tree. As you recall, the update that caused the new > update_seq was not a leaf, at this point we create a #doc_info{} record > with an incorrect high_seq member pointing to the update_seq we are > about to remove from the docinfo_by_seq_tree (remember we calculated the > seq to remove before we consulted the leaves). > > The end result is that we remove the same update_seq we insert. This > sets us up for the real bug. The next time we go to update this document > the same procedure is applied. But what happens is at the point we > calculate the seq to remove from docinfo_by_seq_tree, we calculate the > wrong value. Thus when the update continues we remove an update_seq that > doesn't exist in the tree and insert our new seq. But, the seq from the > previous update is still in the tree. Thus, our docinfo_by_seq_tree now > contains two entries pointing at the same document. > > At this point, we run into the observed behavior of this bug that ends > up causing duplicate entries in views which then ends up throwing errors > when the view is compaction. These errors are also particularly nasty > because they bubble up the the couch_view gen_server which crashes and > spiders out crashing every couch_view_group process. That part probably > isn't important though. > > There's a simple test include with the patch to illustrate the behavior > and maintain an assertion that it stays fixed. > > Fixes COUCHDB-1265 > > > Modified: > couchdb/trunk/share/www/script/test/recreate_doc.js > couchdb/trunk/src/couchdb/couch_doc.erl > couchdb/trunk/src/couchdb/couch_key_tree.erl > > Modified: couchdb/trunk/share/www/script/test/recreate_doc.js > URL: > http://svn.apache.org/viewvc/couchdb/trunk/share/www/script/test/recreate_doc.js?rev=1164350&r1=1164349&r2=1164350&view=diff > ============================================================================== > --- couchdb/trunk/share/www/script/test/recreate_doc.js (original) > +++ couchdb/trunk/share/www/script/test/recreate_doc.js Fri Sep 2 04:31:10 > 2011 > @@ -77,4 +77,45 @@ couchTests.recreate_doc = function(debug > } catch (e) { > T(e.error == "conflict"); > } > + > + db.deleteDb(); > + db.createDb(); > + > + // COUCHDB-1265 > + // Resuscitate an unavailable old revision and make sure that it > + // doesn't introduce duplicates into the _changes feed. > + > + var doc = {_id: "bar", count: 0}; > + T(db.save(doc).ok); > + var ghost = {_id: "bar", _rev: doc._rev, count: doc.count}; > + for(var i = 0; i < 2; i++) { > + doc.count += 1; > + T(db.save(doc).ok); > + } > + > + // Compact so that the old revision to be resuscitated will be > + // in the rev_tree as ?REV_MISSING > + db.compact(); > + while(db.info().compact_running) {} > + > + // Saving the ghost here puts it back in the rev_tree in such > + // a way as to create a new update_seq but without changing a > + // leaf revision. This would cause the #full_doc_info{} and > + // #doc_info{} records to diverge in their idea of what the > + // doc's update_seq is and end up introducing a duplicate in > + // the _changes feed the next time this doc is updated. > + T(db.save(ghost, {new_edits: false}).ok); > + > + // The duplicate would have been introduce here becuase the #doc_info{} > + // would not have been removed correctly. > + T(db.save(doc).ok); > + > + // And finally assert that there are no duplicates in _changes. > + var req = CouchDB.request("GET", "/test_suite_db/_changes"); > + var resp = JSON.parse(req.responseText); > + var docids = {}; > + for(var i = 0; i < resp.results.length; i++) { > + T(docids[resp.results[i].id] === undefined, "Duplicates in _changes > feed."); > + docids[resp.results[i].id] = true; > + } > }; > > Modified: couchdb/trunk/src/couchdb/couch_doc.erl > URL: > http://svn.apache.org/viewvc/couchdb/trunk/src/couchdb/couch_doc.erl?rev=1164350&r1=1164349&r2=1164350&view=diff > ============================================================================== > --- couchdb/trunk/src/couchdb/couch_doc.erl (original) > +++ couchdb/trunk/src/couchdb/couch_doc.erl Fri Sep 2 04:31:10 2011 > @@ -319,10 +319,19 @@ to_doc_info(FullDocInfo) -> > {DocInfo, _Path} = to_doc_info_path(FullDocInfo), > DocInfo. > > -max_seq([], Max) -> > - Max; > -max_seq([#rev_info{seq=Seq}|Rest], Max) -> > - max_seq(Rest, if Max > Seq -> Max; true -> Seq end). > +max_seq(Tree) -> > + FoldFun = fun({_Pos, _Key}, Value, _Type, MaxOldSeq) -> > + case Value of > + {_Deleted, _DiskPos, OldTreeSeq} -> > + % Older versions didn't track data sizes. > + erlang:max(MaxOldSeq, OldTreeSeq); > + {_Deleted, _DiskPos, OldTreeSeq, _Size} -> > + erlang:max(MaxOldSeq, OldTreeSeq); > + _ -> > + MaxOldSeq > + end > + end, > + couch_key_tree:fold(FoldFun, 0, Tree). > > to_doc_info_path(#full_doc_info{id=Id,rev_tree=Tree}) -> > RevInfosAndPath = [ > @@ -342,7 +351,7 @@ to_doc_info_path(#full_doc_info{id=Id,re > end, RevInfosAndPath), > [{_RevInfo, WinPath}|_] = SortedRevInfosAndPath, > RevInfos = [RevInfo || {RevInfo, _Path} <- SortedRevInfosAndPath], > - {#doc_info{id=Id, high_seq=max_seq(RevInfos, 0), revs=RevInfos}, > WinPath}. > + {#doc_info{id=Id, high_seq=max_seq(Tree), revs=RevInfos}, WinPath}. > > > > > Modified: couchdb/trunk/src/couchdb/couch_key_tree.erl > URL: > http://svn.apache.org/viewvc/couchdb/trunk/src/couchdb/couch_key_tree.erl?rev=1164350&r1=1164349&r2=1164350&view=diff > ============================================================================== > --- couchdb/trunk/src/couchdb/couch_key_tree.erl (original) > +++ couchdb/trunk/src/couchdb/couch_key_tree.erl Fri Sep 2 04:31:10 2011 > @@ -49,7 +49,7 @@ > > -export([merge/3, find_missing/2, get_key_leafs/2, get_full_key_paths/2, > get/2]). > -export([get_all_leafs/1, count_leafs/1, remove_leafs/2, > get_all_leafs_full/1, stem/2]). > --export([map/2, mapfold/3, map_leafs/2]). > +-export([map/2, mapfold/3, map_leafs/2, fold/3]). > > -include("couch_db.hrl"). > > @@ -320,6 +320,21 @@ count_leafs_simple([{_Key, _Value, SubTr > count_leafs_simple(SubTree) + count_leafs_simple(RestTree). > > > +fold(_Fun, Acc, []) -> > + Acc; > +fold(Fun, Acc0, [{Pos, Tree}|Rest]) -> > + Acc1 = fold_simple(Fun, Acc0, Pos, [Tree]), > + fold(Fun, Acc1, Rest). > + > +fold_simple(_Fun, Acc, _Pos, []) -> > + Acc; > +fold_simple(Fun, Acc0, Pos, [{Key, Value, SubTree} | RestTree]) -> > + Type = if SubTree == [] -> leaf; true -> branch end, > + Acc1 = Fun({Pos, Key}, Value, Type, Acc0), > + Acc2 = fold_simple(Fun, Acc1, Pos+1, SubTree), > + fold_simple(Fun, Acc2, Pos, RestTree). > + > + > map(_Fun, []) -> > []; > map(Fun, [{Pos, Tree}|Rest]) -> > > >
