couchdb-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Adam Kocoloski <adam.kocolo...@gmail.com>
Subject Re: svn commit: r1164350 - in /couchdb/trunk: share/www/script/test/recreate_doc.js src/couchdb/couch_doc.erl src/couchdb/couch_key_tree.erl
Date Fri, 02 Sep 2011 14:12:09 GMT
The part that I didn't quite get was the following 

> 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.

Do we end up selecting the sequence from the non-leaf revision? Best,

Adam 


On Friday, September 2, 2011 at 6:29 AM, Dave Cottlehuber wrote:

> Paul,
> 
> Love your work mate! Outstanding commit msg, I'm working through it (slowly).
> 
> A+
> D
> 
> On 2 September 2011 16:31, <davisp@apache.org (mailto:davisp@apache.org)> 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 (http://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]) ->



Mime
View raw message