From 6fdc0f0ae77d6aaefd175277fa8355089f41806a Mon Sep 17 00:00:00 2001
From: Magnus Ahltorp <map@kth.se>
Date: Wed, 28 Jan 2015 17:29:58 +0100
Subject: Perform frontend index writes in two phases

---
 src/db.erl       | 25 ++++++++++++++++++-------
 src/frontend.erl |  6 +++++-
 src/perm.erl     | 26 ++++++++++++++++++++------
 3 files changed, 43 insertions(+), 14 deletions(-)

diff --git a/src/db.erl b/src/db.erl
index d2e0814..0541678 100644
--- a/src/db.erl
+++ b/src/db.erl
@@ -6,10 +6,11 @@
 
 %% API.
 -export([start_link/0, stop/0]).
--export([add/2, add_entryhash/2, add_index/2, set_treesize/1, size/0]).
+-export([add/2, add_entryhash/2, add_index_nosync/2, set_treesize/1, size/0]).
 -export([get_by_index/1, get_by_indices/3, get_by_leaf_hash/1]).
 -export([get_by_entry_hash/1, entry_for_leafhash/1, leafhash_for_index/1]).
 -export([leafhash_for_indices/2, indexsize/0]).
+-export([indexforhash_sync/2, index_sync/0]).
 %% gen_server callbacks.
 -export([init/1, handle_call/3, terminate/2, handle_cast/2, handle_info/2,
          code_change/3]).
@@ -48,9 +49,9 @@ add_entryhash(LeafHash, EntryHash) ->
     ok = perm:ensurefile(entryhash_root_path(), EntryHash, LeafHash),
     ok.
 
--spec add_index(binary(), non_neg_integer()) -> ok.
-add_index(LeafHash, Index) ->
-    call(?MODULE, {add_index, {LeafHash, Index}}).
+-spec add_index_nosync(binary(), non_neg_integer()) -> ok.
+add_index_nosync(LeafHash, Index) ->
+    call(?MODULE, {add_index_nosync, {LeafHash, Index}}).
 
 -spec set_treesize(non_neg_integer()) -> ok.
 set_treesize(Size) ->
@@ -177,8 +178,18 @@ get_by_indices_helper(Start, End) ->
 handle_call(stop, _From, State) ->
     {stop, normal, stopped, State};
 
-handle_call({add_index, {LeafHash, Index}}, _From, State) ->
-    ok = perm:ensurefile(indexforhash_root_path(),
-                         LeafHash, integer_to_binary(Index)),
+handle_call({add_index_nosync, {LeafHash, Index}}, _From, State) ->
+    ok = perm:ensurefile_nosync(indexforhash_root_path(),
+                                LeafHash, integer_to_binary(Index)),
     ok = index:add(index_path(), Index, LeafHash),
     {reply, ok, State}.
+
+indexforhash_sync(LeafHash, Index) ->
+    ok = perm:ensurefile(indexforhash_root_path(),
+                         LeafHash, integer_to_binary(Index)),
+    ok.
+
+index_sync() ->
+    Basepath = index_path(),
+    ok = util:fsync([Basepath, filename:dirname(Basepath)]),
+    ok.
diff --git a/src/frontend.erl b/src/frontend.erl
index 6fc2fd5..b2244de 100644
--- a/src/frontend.erl
+++ b/src/frontend.erl
@@ -29,8 +29,12 @@ request(post, "ct/frontend/sendlog", Input) ->
 
             Indices = lists:seq(Start, Start + length(Hashes) - 1),
             lists:foreach(fun ({Hash, Index}) ->
-                                  ok = db:add_index(Hash, Index)
+                                  ok = db:add_index_nosync(Hash, Index)
                           end, lists:zip(Hashes, Indices)),
+            lists:foreach(fun ({Hash, Index}) ->
+                                  ok = db:indexforhash_sync(Hash, Index)
+                          end, lists:zip(Hashes, Indices)),
+            ok = db:index_sync(),
             success({[{result, <<"ok">>}]})
     end;
 
diff --git a/src/perm.erl b/src/perm.erl
index 9f02b55..614656a 100644
--- a/src/perm.erl
+++ b/src/perm.erl
@@ -2,7 +2,7 @@
 %%% See LICENSE for licensing information.
 
 -module(perm).
--export([ensurefile/3, readfile/2]).
+-export([ensurefile/3, ensurefile_nosync/3, readfile/2]).
 
 -spec readfile_and_verify(string(), binary()) -> ok | differ | {error, atom()}.
 readfile_and_verify(Name, Content) ->
@@ -49,13 +49,21 @@ path_for_key(Rootdir, Key) ->
 
 -spec ensurefile(string(), binary(), binary()) -> ok | differ.
 ensurefile(Rootdir, Key, Content) ->
+    ensurefile(Rootdir, Key, Content, sync).
+
+-spec ensurefile_nosync(string(), binary(), binary()) -> ok | differ.
+ensurefile_nosync(Rootdir, Key, Content) ->
+    ensurefile(Rootdir, Key, Content, nosync).
+
+ensurefile(Rootdir, Key, Content, Syncflag) ->
     lager:debug("dir ~p key ~p", [Rootdir, Key]),
     {Dirs, Path} = path_for_key(Rootdir, Key),
     case readfile_and_verify(Path, Content) of
 	ok ->
             lager:debug("key ~p existed, fsync", [Key]),
-	    util:fsync([Path, Rootdir | Dirs]),
-            lager:debug("key ~p fsynced", [Key]);
+	    ok = util:fsync([Path, Rootdir | Dirs]),
+            lager:debug("key ~p fsynced", [Key]),
+            ok;
         differ ->
             lager:debug("key ~p existed, was different", [Key]),
             differ;
@@ -67,9 +75,15 @@ ensurefile(Rootdir, Key, Content) ->
             NurseryName = Rootdir ++ "nursery/" ++
                 util:tempfilename(hex:bin_to_hexstr(Key)),
             util:write_tempfile_and_rename(Path, NurseryName, Content),
-            lager:debug("key ~p added, fsync", [Key]),
-            util:fsync([Path, Rootdir | Dirs]),
-            lager:debug("key ~p fsynced", [Key]);
+            case Syncflag of
+                sync ->
+                    lager:debug("key ~p added, fsync", [Key]),
+                    ok = util:fsync([Path, Rootdir | Dirs]),
+                    lager:debug("key ~p fsynced", [Key]),
+                    ok;
+                nosync ->
+                    ok
+            end;
 	{error, Error} ->
             util:exit_with_error(Error, readfile, "Error reading file")
     end.
-- 
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