Improve compaction task status updates

Previous the emsort related operations did not update the compaction
task status. For large databases this leads to some very long waits
while the compaction task stays at 100%. This change adds progress
reports to the steps for sorting and copying document ids back into the
database file.

Author: davisp

src/couch_db_updater.erl

@@ -1147,6 +1147,7 @@ copy_compact(Db, NewDb0, Retry) ->
     TaskProps0 = [
         {type, database_compaction},
         {database, Db#db.name},
+        {phase, seq_tree},
         {progress, 0},
         {changes_done, 0},
         {total_changes, TotalChanges}
@@ -1193,6 +1194,8 @@ start_copy_compact(#db{}=Db) ->
         open_compaction_files(Name, Header, Filepath, Options),
     erlang:monitor(process, MFd),
 
+    {ok, DocCount} = couch_db:get_doc_count(Db),
+
     % This is a bit worrisome. init_db/4 will monitor the data fd
     % but it doesn't know about the meta fd. For now I'll maintain
     % that the data fd is the old normal fd and meta fd is special
@@ -1201,9 +1204,9 @@ start_copy_compact(#db{}=Db) ->
 
     NewDb1 = copy_purge_info(Db, NewDb),
     NewDb2 = copy_compact(Db, NewDb1, Retry),
-    NewDb3 = sort_meta_data(NewDb2),
+    NewDb3 = sort_meta_data(NewDb2, DocCount),
     NewDb4 = commit_compaction_data(NewDb3),
-    NewDb5 = copy_meta_data(NewDb4),
+    NewDb5 = copy_meta_data(NewDb4, DocCount),
     NewDb6 = sync_header(NewDb5, db_to_header(NewDb5, NewDb5#db.header)),
     close_db(NewDb6),
 
@@ -1323,12 +1326,82 @@ bind_id_tree(Db, Fd, State) ->
     Db#db{id_tree=IdBtree}.
 
 
-sort_meta_data(Db0) ->
-    {ok, Ems} = couch_emsort:merge(Db0#db.id_tree),
-    Db0#db{id_tree=Ems}.
+sort_meta_data(Db0, DocCount) ->
+    couch_task_status:update([
+        {phase, sort_ids_init},
+        {total_changes, DocCount},
+        {changes_done, 0},
+        {progress, 0}
+    ]),
+    Ems0 = Db0#db.id_tree,
+    Options = [
+        {event_cb, fun emsort_cb/3},
+        {event_st, {init, 0, 0}}
+    ],
+    Ems1 = couch_emsort:set_options(Ems0, Options),
+    {ok, Ems2} = couch_emsort:merge(Ems1),
+    Db0#db{id_tree=Ems2}.
+
+
+emsort_cb(_Ems, {merge, chain}, {init, Copied, Nodes}) ->
+    {init, Copied, Nodes + 1};
+emsort_cb(_Ems, row_copy, {init, Copied, Nodes}) when Copied >= 1000 ->
+    update_compact_task(Copied + 1),
+    {init, 0, Nodes};
+emsort_cb(_Ems, row_copy, {init, Copied, Nodes}) ->
+    {init, Copied + 1, Nodes};
+emsort_cb(Ems, {merge_start, reverse}, {init, Copied, Nodes}) ->
+    BBChunkSize = couch_emsort:get_bb_chunk_size(Ems),
+
+    % Subtract one because we already finished the first
+    % iteration when we were counting the number of nodes
+    % in the backbone.
+    Iters = calculate_sort_iters(Nodes, BBChunkSize, 0) - 1,
+
+    % Compaction retries mean we may have copied more than
+    % doc count rows. This accounts for that by using the
+    % number we've actually copied.
+    [PrevCopied] = couch_task_status:get([changes_done]),
+    TotalCopied = PrevCopied + Copied,
+
+    couch_task_status:update([
+        {phase, sort_ids},
+        {total_changes, Iters * TotalCopied},
+        {changes_done, 0},
+        {progress, 0}
+    ]),
+    0;
+
+emsort_cb(_Ems, row_copy, Copied) when is_integer(Copied), Copied > 1000 ->
+    update_compact_task(Copied + 1),
+    0;
+
+emsort_cb(_Ems, row_copy, Copied) when is_integer(Copied) ->
+    Copied + 1;
+
+emsort_cb(_Ems, _Event, St) ->
+    St.
 
 
-copy_meta_data(#db{fd=Fd, header=Header}=Db) ->
+calculate_sort_iters(Nodes, BBChunk, Count) when Nodes < BBChunk ->
+    Count;
+calculate_sort_iters(Nodes0, BBChunk, Count) when BBChunk > 1 ->
+    Calc = fun(N0) ->
+        N1 = N0 div BBChunk,
+        N1 + if N1 rem BBChunk == 0 -> 0; true -> 1 end
+    end,
+    Nodes1 = Calc(Nodes0),
+    Nodes2 = Calc(Nodes1),
+    calculate_sort_iters(Nodes2, BBChunk, Count + 2).
+
+
+copy_meta_data(#db{fd=Fd, header=Header}=Db, DocCount) ->
+    couch_task_status:update([
+        {phase, copy_ids},
+        {changes_done, 0},
+        {total_changes, DocCount},
+        {progress, 0}
+    ]),
     Src = Db#db.id_tree,
     DstState = couch_db_header:id_tree_state(Header),
     {ok, IdTree0} = couch_btree:open(DstState, Fd, [
@@ -1348,6 +1421,7 @@ copy_meta_data(#db{fd=Fd, header=Header}=Db) ->
     {ok, SeqTree} = couch_btree:add_remove(
         Acc#merge_st.seq_tree, [], Acc#merge_st.rem_seqs
     ),
+    update_compact_task(length(Acc#merge_st.infos)),
     Db#db{id_tree=IdTree, seq_tree=SeqTree}.
 
 
@@ -1359,6 +1433,7 @@ merge_docids(Iter, #merge_st{infos=Infos}=Acc) when length(Infos) > 1000 ->
     } = Acc,
     {ok, IdTree1} = couch_btree:add(IdTree0, Infos),
     {ok, SeqTree1} = couch_btree:add_remove(SeqTree0, [], RemSeqs),
+    update_compact_task(length(Infos)),
     Acc1 = Acc#merge_st{
         id_tree=IdTree1,
         seq_tree=SeqTree1,

src/couch_emsort.erl

@@ -129,15 +129,18 @@
 %     CA3                  CD3
 %
 
--export([open/1, open/2, get_fd/1, get_state/1]).
+-export([open/1, open/2, set_options/2, get_fd/1, get_state/1]).
+-export([get_bb_chunk_size/1]).
 -export([add/2, merge/1, sort/1, iter/1, next/1]).
 
 
 -record(ems, {
     fd,
     root,
     bb_chunk = 10,
-    chain_chunk = 100
+    chain_chunk = 100,
+    event_cb,
+    event_st
 }).
 
 
@@ -156,7 +159,11 @@ set_options(Ems, [{root, Root} | Rest]) ->
 set_options(Ems, [{chain_chunk, Count} | Rest]) when is_integer(Count) ->
     set_options(Ems#ems{chain_chunk=Count}, Rest);
 set_options(Ems, [{back_bone_chunk, Count} | Rest]) when is_integer(Count) ->
-    set_options(Ems#ems{bb_chunk=Count}, Rest).
+    set_options(Ems#ems{bb_chunk=Count}, Rest);
+set_options(Ems, [{event_cb, EventCB} | Rest]) when is_function(EventCB, 3) ->
+    set_options(Ems#ems{event_cb=EventCB}, Rest);
+set_options(Ems, [{event_st, EventSt} | Rest]) ->
+    set_options(Ems#ems{event_st=EventSt}, Rest).
 
 
 get_fd(#ems{fd=Fd}) ->
@@ -167,6 +174,10 @@ get_state(#ems{root=Root}) ->
     Root.
 
 
+get_bb_chunk_size(#ems{bb_chunk = Size}) ->
+    Size.
+
+
 add(Ems, []) ->
     {ok, Ems};
 add(Ems, KVs) ->
@@ -224,51 +235,55 @@ decimate(#ems{root={_BB, nil}}=Ems) ->
     % We have less than bb_chunk backbone pointers so we're
     % good to start streaming KV's back to the client.
     Ems;
-decimate(#ems{root={BB, NextBB}}=Ems) ->
+decimate(#ems{}=Ems0) ->
     % To make sure we have a bounded amount of data in RAM
     % at any given point we first need to decimate the data
     % by performing the first couple iterations of a merge
     % sort writing the intermediate results back to disk.
 
     % The first pass gives us a sort with pointers linked from
     % largest to smallest.
-    {RevBB, RevNextBB} = merge_back_bone(Ems, small, BB, NextBB),
+    {ok, Ems1} = event_notify(Ems0, {merge_start, forward}),
+    {ok, Ems2} = merge_back_bone(Ems1, small),
 
     % We have to run a second pass so that links are pointed
     % back from smallest to largest.
-    {FwdBB, FwdNextBB} = merge_back_bone(Ems, big, RevBB, RevNextBB),
+    {ok, Ems3} = event_notify(Ems2, {merge_start, reverse}),
+    {ok, Ems4} = merge_back_bone(Ems3, big),
 
     % Continue deicmating until we have an acceptable bound on
     % the number of keys to use.
-    decimate(Ems#ems{root={FwdBB, FwdNextBB}}).
+    decimate(Ems4).
 
 
-merge_back_bone(Ems, Choose, BB, NextBB) ->
-    BBPos = merge_chains(Ems, Choose, BB),
-    merge_rest_back_bone(Ems, Choose, NextBB, {[BBPos], nil}).
+merge_back_bone(#ems{root={BB, NextBB}}=Ems0, Choose) ->
+    {ok, Ems1, BBPos} = merge_chains(Ems0, Choose, BB),
+    merge_rest_back_bone(Ems1, Choose, NextBB, {[BBPos], nil}).
 
 
-merge_rest_back_bone(_Ems, _Choose, nil, Acc) ->
-    Acc;
-merge_rest_back_bone(Ems, Choose, BBPos, Acc) ->
-    {ok, {BB, NextBB}} = couch_file:pread_term(Ems#ems.fd, BBPos),
-    NewPos = merge_chains(Ems, Choose, BB),
-    {NewBB, NewPrev} = append_item(Ems, Acc, NewPos, Ems#ems.bb_chunk),
-    merge_rest_back_bone(Ems, Choose, NextBB, {NewBB, NewPrev}).
+merge_rest_back_bone(Ems, _Choose, nil, Acc) ->
+    {ok, Ems#ems{root=Acc}};
+merge_rest_back_bone(Ems0, Choose, BBPos, Acc) ->
+    {ok, {BB, NextBB}} = couch_file:pread_term(Ems0#ems.fd, BBPos),
+    {ok, Ems1, NewPos} = merge_chains(Ems0, Choose, BB),
+    {NewBB, NewPrev} = append_item(Ems1, Acc, NewPos, Ems1#ems.bb_chunk),
+    merge_rest_back_bone(Ems1, Choose, NextBB, {NewBB, NewPrev}).
 
 
-merge_chains(Ems, Choose, BB) ->
-    Chains = init_chains(Ems, Choose, BB),
-    merge_chains(Ems, Choose, Chains, {[], nil}).
+merge_chains(Ems0, Choose, BB) ->
+    {ok, Ems1} = event_notify(Ems0, {merge, chain}),
+    Chains = init_chains(Ems1, Choose, BB),
+    merge_chains(Ems1, Choose, Chains, {[], nil}).
 
 
 merge_chains(Ems, _Choose, [], ChainAcc) ->
     {ok, CPos, _} = couch_file:append_term(Ems#ems.fd, ChainAcc),
-    CPos;
-merge_chains(#ems{chain_chunk=CC}=Ems, Choose, Chains, Acc) ->
-    {KV, RestChains} = choose_kv(Choose, Ems, Chains),
-    {NewKVs, NewPrev} = append_item(Ems, Acc, KV, CC),
-    merge_chains(Ems, Choose, RestChains, {NewKVs, NewPrev}).
+    {ok, Ems, CPos};
+merge_chains(#ems{chain_chunk=CC}=Ems0, Choose, Chains, Acc) ->
+    {KV, RestChains} = choose_kv(Choose, Ems0, Chains),
+    {NewKVs, NewPrev} = append_item(Ems0, Acc, KV, CC),
+    {ok, Ems1} = event_notify(Ems0, row_copy),
+    merge_chains(Ems1, Choose, RestChains, {NewKVs, NewPrev}).
 
 
 init_chains(Ems, Choose, BB) ->
@@ -316,3 +331,9 @@ append_item(Ems, {List, Prev}, Pos, Size) when length(List) >= Size ->
 append_item(_Ems, {List, Prev}, Pos, _Size) ->
     {[Pos | List], Prev}.
 
+
+event_notify(#ems{event_cb = undefined} = Ems, _) ->
+    {ok, Ems};
+event_notify(#ems{event_cb=EventCB, event_st=EventSt}=Ems, Event) ->
+    NewSt = EventCB(Ems, Event, EventSt),
+    {ok, Ems#ems{event_st=NewSt}}.