Add dedicated couch_file to the DB updater process.

src/couchdb/couch_btree.erl

@@ -16,17 +16,9 @@
 -export([fold/4, full_reduce/1, final_reduce/2, foldl/3, foldl/4]).
 -export([fold_reduce/4, lookup/2, get_state/1, set_options/2]).
 
+-include("couch_db.hrl").
 -define(CHUNK_THRESHOLD, 16#4ff).
 
--record(btree,
-    {fd,
-    root,
-    extract_kv = fun({Key, Value}) -> {Key, Value} end,
-    assemble_kv =  fun(Key, Value) -> {Key, Value} end,
-    less = fun(A, B) -> A < B end,
-    reduce = nil
-    }).
-
 extract(#btree{extract_kv=Extract}, Value) ->
     Extract(Value).
 

src/couchdb/couch_db.erl

@@ -223,7 +223,7 @@ get_full_doc_info(Db, Id) ->
     Result.
 
 get_full_doc_infos(Db, Ids) ->
-    couch_btree:lookup(Db#db.fulldocinfo_by_id_btree, Ids).
+    couch_btree:lookup(by_id_btree(Db), Ids).
 
 increment_update_seq(#db{update_pid=UpdatePid}) ->
     gen_server:call(UpdatePid, increment_update_seq).
@@ -251,11 +251,10 @@ get_db_info(Db) ->
         compactor_pid=Compactor,
         update_seq=SeqNum,
         name=Name,
-        fulldocinfo_by_id_btree=FullDocBtree,
         instance_start_time=StartTime,
         committed_update_seq=CommittedUpdateSeq} = Db,
     {ok, Size} = couch_file:bytes(Fd),
-    {ok, {Count, DelCount}} = couch_btree:full_reduce(FullDocBtree),
+    {ok, {Count, DelCount}} = couch_btree:full_reduce(by_id_btree(Db)),
     InfoList = [
         {db_name, Name},
         {doc_count, Count},
@@ -270,8 +269,8 @@ get_db_info(Db) ->
         ],
     {ok, InfoList}.
 
-get_design_docs(#db{fulldocinfo_by_id_btree=Btree}=Db) ->
-    {ok,_, Docs} = couch_btree:fold(Btree,
+get_design_docs(Db) ->
+    {ok,_, Docs} = couch_btree:fold(by_id_btree(Db),
         fun(#full_doc_info{id= <<"_design/",_/binary>>}=FullDocInfo, _Reds, AccDocs) ->
             {ok, Doc} = couch_db:open_doc_int(Db, FullDocInfo, []),
             {ok, [Doc | AccDocs]};
@@ -662,7 +661,7 @@ update_docs(Db, Docs, Options, replicated_changes) ->
         DocErrors = [],
         DocBuckets3 = DocBuckets
     end,
-    DocBuckets4 = [[doc_flush_atts(check_dup_atts(Doc), Db#db.fd)
+    DocBuckets4 = [[doc_flush_atts(check_dup_atts(Doc), Db#db.updater_fd)
             || Doc <- Bucket] || Bucket <- DocBuckets3],
     {ok, []} = write_and_commit(Db, DocBuckets4, [], [merge_conflicts | Options]),
     {ok, DocErrors};
@@ -718,7 +717,7 @@ update_docs(Db, Docs, Options, interactive_edit) ->
                 true -> [] end ++ Options,
         DocBuckets3 = [[
                 doc_flush_atts(set_new_att_revpos(
-                        check_dup_atts(Doc)), Db#db.fd)
+                        check_dup_atts(Doc)), Db#db.updater_fd)
                 || Doc <- B] || B <- DocBuckets2],
         {DocBuckets4, IdRevs} = new_revs(DocBuckets3, [], []),
 
@@ -786,7 +785,10 @@ write_and_commit(#db{update_pid=UpdatePid}=Db, DocBuckets,
             % This can happen if the db file we wrote to was swapped out by
             % compaction. Retry by reopening the db and writing to the current file
             {ok, Db2} = open_ref_counted(Db#db.main_pid, self()),
-            DocBuckets2 = [[doc_flush_atts(Doc, Db2#db.fd) || Doc <- Bucket] || Bucket <- DocBuckets],
+            DocBuckets2 = [
+                [doc_flush_atts(Doc, Db2#db.updater_fd) || Doc <- Bucket] ||
+                Bucket <- DocBuckets
+            ],
             % We only retry once
             close(Db2),
             UpdatePid ! {update_docs, self(), DocBuckets2, NonRepDocs, MergeConflicts, FullCommit},
@@ -954,25 +956,28 @@ changes_since(Db, Style, StartSeq, Fun, Options, Acc) ->
             end,
             Fun(DocInfo2, Acc2)
         end,
-    {ok, _LastReduction, AccOut} = couch_btree:fold(Db#db.docinfo_by_seq_btree,
+    {ok, _LastReduction, AccOut} = couch_btree:fold(by_seq_btree(Db),
         Wrapper, Acc, [{start_key, StartSeq + 1}] ++ Options),
     {ok, AccOut}.
 
 count_changes_since(Db, SinceSeq) ->
+    BTree = by_seq_btree(Db),
     {ok, Changes} =
-    couch_btree:fold_reduce(Db#db.docinfo_by_seq_btree,
+    couch_btree:fold_reduce(BTree,
         fun(_SeqStart, PartialReds, 0) ->
-            {ok, couch_btree:final_reduce(Db#db.docinfo_by_seq_btree, PartialReds)}
+            {ok, couch_btree:final_reduce(BTree, PartialReds)}
         end,
         0, [{start_key, SinceSeq + 1}]),
     Changes.
 
 enum_docs_since(Db, SinceSeq, InFun, Acc, Options) ->
-    {ok, LastReduction, AccOut} = couch_btree:fold(Db#db.docinfo_by_seq_btree, InFun, Acc, [{start_key, SinceSeq + 1} | Options]),
+    {ok, LastReduction, AccOut} = couch_btree:fold(
+        by_seq_btree(Db), InFun, Acc, [{start_key, SinceSeq + 1} | Options]),
     {ok, enum_docs_since_reduce_to_count(LastReduction), AccOut}.
 
 enum_docs(Db, InFun, InAcc, Options) ->
-    {ok, LastReduce, OutAcc} = couch_btree:fold(Db#db.fulldocinfo_by_id_btree, InFun, InAcc, Options),
+    {ok, LastReduce, OutAcc} = couch_btree:fold(
+        by_id_btree(Db), InFun, InAcc, Options),
     {ok, enum_docs_reduce_to_count(LastReduce), OutAcc}.
 
 % server functions
@@ -1072,7 +1077,7 @@ open_doc_revs_int(Db, IdRevs, Options) ->
         IdRevs, LookupResults).
 
 open_doc_int(Db, <<?LOCAL_DOC_PREFIX, _/binary>> = Id, _Options) ->
-    case couch_btree:lookup(Db#db.local_docs_btree, [Id]) of
+    case couch_btree:lookup(local_btree(Db), [Id]) of
     [{ok, {_, {Rev, BodyData}}}] ->
         {ok, #doc{id=Id, revs={0, [list_to_binary(integer_to_list(Rev))]}, body=BodyData}};
     [not_found] ->
@@ -1151,7 +1156,7 @@ doc_to_tree_simple(Doc, [RevId | Rest]) ->
     [{RevId, ?REV_MISSING, doc_to_tree_simple(Doc, Rest)}].
 
 
-make_doc(#db{fd=Fd}=Db, Id, Deleted, Bp, RevisionPath) ->
+make_doc(#db{updater_fd = Fd} = Db, Id, Deleted, Bp, RevisionPath) ->
     {BodyData, Atts} =
     case Bp of
     nil ->
@@ -1207,7 +1212,19 @@ make_doc(#db{fd=Fd}=Db, Id, Deleted, Bp, RevisionPath) ->
         }.
 
 
-increment_stat(#db{is_sys_db = true}, _Stat) ->
-    ok;
-increment_stat(#db{}, Stat) ->
-    couch_stats_collector:increment(Stat).
+increment_stat(#db{options = Options}, Stat) ->
+    case lists:member(sys_db, Options) of
+    true ->
+        ok;
+    false ->
+        couch_stats_collector:increment(Stat)
+    end.
+
+local_btree(#db{local_docs_btree = BTree, fd = ReaderFd}) ->
+    BTree#btree{fd = ReaderFd}.
+
+by_seq_btree(#db{docinfo_by_seq_btree = BTree, fd = ReaderFd}) ->
+    BTree#btree{fd = ReaderFd}.
+
+by_id_btree(#db{fulldocinfo_by_id_btree = BTree, fd = ReaderFd}) ->
+    BTree#btree{fd = ReaderFd}.

src/couchdb/couch_db.hrl

@@ -158,6 +158,7 @@
     compactor_pid = nil,
     instance_start_time, % number of microsecs since jan 1 1970 as a binary string
     fd,
+    updater_fd,
     fd_ref_counter,
     header = #db_header{},
     committed_update_seq,
@@ -174,7 +175,7 @@
     waiting_delayed_commit = nil,
     revs_limit = 1000,
     fsync_options = [],
-    is_sys_db = false
+    options = []
     }).
 
 
@@ -297,3 +298,11 @@
     db_open_options = []
 }).
 
+-record(btree, {
+    fd,
+    root,
+    extract_kv = fun({_Key, _Value} = KV) -> KV end,
+    assemble_kv = fun(Key, Value) -> {Key, Value} end,
+    less = fun(A, B) -> A < B end,
+    reduce = nil
+}).

src/couchdb/couch_db_updater.erl

@@ -42,13 +42,14 @@ init({MainPid, DbName, Filepath, Fd, Options}) ->
             file:delete(Filepath ++ ".compact")
         end
     end,
-
-    Db = init_db(DbName, Filepath, Fd, Header),
+    ReaderFd = open_reader_fd(Filepath, Options),
+    Db = init_db(DbName, Filepath, Fd, ReaderFd, Header, Options),
     Db2 = refresh_validate_doc_funs(Db),
-    {ok, Db2#db{main_pid = MainPid, is_sys_db = lists:member(sys_db, Options)}}.
+    {ok, Db2#db{main_pid = MainPid}}.
 
 
 terminate(_Reason, Db) ->
+    couch_file:close(Db#db.updater_fd),
     couch_file:close(Db#db.fd),
     couch_util:shutdown_sync(Db#db.compactor_pid),
     couch_util:shutdown_sync(Db#db.fd_ref_counter),
@@ -67,7 +68,7 @@ handle_call(increment_update_seq, _From, Db) ->
     {reply, {ok, Db2#db.update_seq}, Db2};
 
 handle_call({set_security, NewSec}, _From, Db) ->
-    {ok, Ptr} = couch_file:append_term(Db#db.fd, NewSec),
+    {ok, Ptr} = couch_file:append_term(Db#db.updater_fd, NewSec),
     Db2 = commit_data(Db#db{security=NewSec, security_ptr=Ptr,
             update_seq=Db#db.update_seq+1}),
     ok = gen_server:call(Db2#db.main_pid, {db_updated, Db2}),
@@ -84,7 +85,7 @@ handle_call({purge_docs, _IdRevs}, _From,
     {reply, {error, purge_during_compaction}, Db};
 handle_call({purge_docs, IdRevs}, _From, Db) ->
     #db{
-        fd=Fd,
+        updater_fd = Fd,
         fulldocinfo_by_id_btree = DocInfoByIdBTree,
         docinfo_by_seq_btree = DocInfoBySeqBTree,
         update_seq = LastSeq,
@@ -161,9 +162,10 @@ handle_call(start_compact, _From, Db) ->
 
 handle_cast({compact_done, CompactFilepath}, #db{filepath=Filepath}=Db) ->
     {ok, NewFd} = couch_file:open(CompactFilepath),
+    ReaderFd = open_reader_fd(CompactFilepath, Db#db.options),
     {ok, NewHeader} = couch_file:read_header(NewFd),
     #db{update_seq=NewSeq} = NewDb =
-            init_db(Db#db.name, Filepath, NewFd, NewHeader),
+        init_db(Db#db.name, Filepath, NewFd, ReaderFd, NewHeader, Db#db.options),
     unlink(NewFd),
     case Db#db.update_seq == NewSeq of
     true ->
@@ -362,7 +364,7 @@ simple_upgrade_record(Old, New) when tuple_size(Old) < tuple_size(New) ->
     list_to_tuple(tuple_to_list(Old) ++ NewValuesTail).
 
 
-init_db(DbName, Filepath, Fd, Header0) ->
+init_db(DbName, Filepath, Fd, ReaderFd, Header0, Options) ->
     Header1 = simple_upgrade_record(Header0, #db_header{}),
     Header =
     case element(2, Header1) of
@@ -403,10 +405,11 @@ init_db(DbName, Filepath, Fd, Header0) ->
     {MegaSecs, Secs, MicroSecs} = now(),
     StartTime = ?l2b(io_lib:format("~p",
             [(MegaSecs*1000000*1000000) + (Secs*1000000) + MicroSecs])),
-    {ok, RefCntr} = couch_ref_counter:start([Fd]),
+    {ok, RefCntr} = couch_ref_counter:start([Fd, ReaderFd]),
     #db{
         update_pid=self(),
-        fd=Fd,
+        fd = ReaderFd,
+        updater_fd = Fd,
         fd_ref_counter = RefCntr,
         header=Header,
         fulldocinfo_by_id_btree = IdBtree,
@@ -420,9 +423,19 @@ init_db(DbName, Filepath, Fd, Header0) ->
         security_ptr = SecurityPtr,
         instance_start_time = StartTime,
         revs_limit = Header#db_header.revs_limit,
-        fsync_options = FsyncOptions
+        fsync_options = FsyncOptions,
+        options = Options
         }.
 
+open_reader_fd(Filepath, Options) ->
+    {ok, Fd} = case lists:member(sys_db, Options) of
+    true ->
+        couch_file:open(Filepath, [read_only, sys_db]);
+    false ->
+        couch_file:open(Filepath, [read_only])
+    end,
+    unlink(Fd),
+    Fd.
 
 close_db(#db{fd_ref_counter = RefCntr}) ->
     couch_ref_counter:drop(RefCntr).
@@ -443,7 +456,7 @@ refresh_validate_doc_funs(Db) ->
 
 flush_trees(_Db, [], AccFlushedTrees) ->
     {ok, lists:reverse(AccFlushedTrees)};
-flush_trees(#db{fd=Fd,header=Header}=Db,
+flush_trees(#db{updater_fd = Fd, header = Header} = Db,
         [InfoUnflushed | RestUnflushed], AccFlushed) ->
     #full_doc_info{update_seq=UpdateSeq, rev_tree=Unflushed} = InfoUnflushed,
     Flushed = couch_key_tree:map(
@@ -694,7 +707,7 @@ commit_data(Db, true) ->
     Db;
 commit_data(Db, _) ->
     #db{
-        fd = Fd,
+        updater_fd = Fd,
         filepath = Filepath,
         header = OldHeader,
         fsync_options = FsyncOptions,
@@ -723,7 +736,8 @@ commit_data(Db, _) ->
     end.
 
 
-copy_doc_attachments(#db{fd=SrcFd}=SrcDb, {Pos,_RevId}, SrcSp, DestFd) ->
+copy_doc_attachments(#db{updater_fd = SrcFd} = SrcDb, {Pos,_RevId},
+    SrcSp, DestFd) ->
     {ok, {BodyData, BinInfos}} = couch_db:read_doc(SrcDb, SrcSp),
     % copy the bin values
     NewBinInfos = lists:map(
@@ -775,7 +789,7 @@ copy_rev_tree_attachments(SrcDb, DestFd, Tree) ->
         end, Tree).
 
 
-copy_docs(Db, #db{fd=DestFd}=NewDb, InfoBySeq, Retry) ->
+copy_docs(Db, #db{updater_fd = DestFd} = NewDb, InfoBySeq, Retry) ->
     Ids = [Id || #doc_info{id=Id} <- InfoBySeq],
     LookupResults = couch_btree:lookup(Db#db.fulldocinfo_by_id_btree, Ids),
 
@@ -851,7 +865,7 @@ copy_compact(Db, NewDb0, Retry) ->
 
     % copy misc header values
     if NewDb3#db.security /= Db#db.security ->
-        {ok, Ptr} = couch_file:append_term(NewDb3#db.fd, Db#db.security),
+        {ok, Ptr} = couch_file:append_term(NewDb3#db.updater_fd, Db#db.security),
         NewDb4 = NewDb3#db{security=Db#db.security, security_ptr=Ptr};
     true ->
         NewDb4 = NewDb3
@@ -873,7 +887,8 @@ start_copy_compact(#db{name=Name,filepath=Filepath}=Db) ->
         Retry = false,
         ok = couch_file:write_header(Fd, Header=#db_header{})
     end,
-    NewDb = init_db(Name, CompactFile, Fd, Header),
+    ReaderFd = open_reader_fd(CompactFile, Db#db.options),
+    NewDb = init_db(Name, CompactFile, Fd, ReaderFd, Header, Db#db.options),
     unlink(Fd),
     NewDb2 = copy_compact(Db, NewDb, Retry),
     close_db(NewDb2),