From 8c48a13e1f996b5aa49497031737dee6818dc331 Mon Sep 17 00:00:00 2001
From: Magnus Ahltorp <map@kth.se>
Date: Tue, 15 Mar 2016 23:42:35 +0100
Subject: Added caching of first entry not known to be present

---
 src/frontend.erl | 39 +++++++++++++++++++++++++++++++++++++--
 src/plop_app.erl |  1 +
 2 files changed, 38 insertions(+), 2 deletions(-)

(limited to 'src')

diff --git a/src/frontend.erl b/src/frontend.erl
index 04e307c..3dbf3af 100644
--- a/src/frontend.erl
+++ b/src/frontend.erl
@@ -5,7 +5,7 @@
 
 -module(frontend).
 %% API (URL)
--export([request/4]).
+-export([request/4, init_module/0]).
 
 -define(APPURL_PLOP_FRONTEND, "plop/v1/frontend").
 -define(APPURL_PLOP_MERGE, "plop/v1/merge").
@@ -324,9 +324,43 @@ prefetchindices(Index, []) ->
 prefetchindices(_Index, PrefetchList) ->
     PrefetchList.
 
+-define(FIRST_UNKNOWN_CACHE_TABLE, missingentries_first_unknown_cache).
+
+init_module() ->
+    create_first_unknown_cache_table().
+
+create_first_unknown_cache_table() ->
+    case ets:info(?FIRST_UNKNOWN_CACHE_TABLE) of
+	undefined ->
+	    ok;
+	_ ->
+	    ets:delete(?FIRST_UNKNOWN_CACHE_TABLE)
+    end,
+    ets:new(?FIRST_UNKNOWN_CACHE_TABLE, [set, public, named_table]).
+
+first_unknown_cache() ->
+    case ets:lookup(?FIRST_UNKNOWN_CACHE_TABLE, first_unknown_cache) of
+        [{_, Size}] ->
+            Size;
+        [] ->
+            0
+    end.
+
+set_first_unknown_cache(Size) ->
+    CurrentSize = first_unknown_cache(),
+    if
+        Size == CurrentSize + 1 ->
+            true = ets:insert(?FIRST_UNKNOWN_CACHE_TABLE, {first_unknown_cache, Size});
+        true ->
+            ok
+    end,
+    ok.
+
+
 -spec fetchmissingentries(non_neg_integer(), non_neg_integer()) -> [binary() | noentry].
 fetchmissingentries(Index, MaxEntries) ->
-    lists:reverse(fetchmissingentries(Index, [], [], MaxEntries)).
+    Index2 = lists:max([first_unknown_cache(), Index]),
+    lists:reverse(fetchmissingentries(Index2, [], [], MaxEntries)).
 
 -spec fetchmissingentries(non_neg_integer(), [binary() | noentry], [binary()], non_neg_integer()) ->
                                  [binary() | noentry].
@@ -343,6 +377,7 @@ fetchmissingentries(Index, Acc, PrefetchList, MaxEntries) ->
                     lager:debug("didn't find hash ~p", [Hash]),
                     fetchmissingentries(Index + 1, [Hash | Acc], PrefetchRest, MaxEntries - 1);
                 _ ->
+                    set_first_unknown_cache(Index + 1),
                     fetchmissingentries(Index + 1, Acc, PrefetchRest, MaxEntries)
             end
     end.
diff --git a/src/plop_app.erl b/src/plop_app.erl
index 611012a..721623c 100644
--- a/src/plop_app.erl
+++ b/src/plop_app.erl
@@ -11,6 +11,7 @@ start(normal, Args) ->
     plop:initsize(),
     perm:init_module(),
     index:init_module(),
+    frontend:init_module(),
     plop_sup:start_link(Args).
 
 stop(_State) ->
-- 
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