From 2a106d0dc58f45d557ddccc14575305616fe5854 Mon Sep 17 00:00:00 2001
From: martinsumner <martin.sumner@adaptip.co.uk>
Date: Tue, 13 Dec 2016 19:38:14 +0000
Subject: [PATCH] Experiment with temporary us eof ETS table

Rather than expensive lists:ukeymerge, try use a temporary ETS table.
---
 src/leveled_pmem.erl | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/src/leveled_pmem.erl b/src/leveled_pmem.erl
index 0c61acf..aee7f7f 100644
--- a/src/leveled_pmem.erl
+++ b/src/leveled_pmem.erl
@@ -102,14 +102,16 @@ check_index(Hash, L0Index) ->
 
 to_list(Slots, FetchFun) ->
     SW = os:timestamp(),
-    SlotList = lists:reverse(lists:seq(1, Slots)),
-    FullList = lists:foldl(fun(Slot, Acc) ->
-                                Tree = FetchFun(Slot),
-                                L = leveled_skiplist:to_list(Tree),
-                                lists:ukeymerge(1, Acc, L)
-                                end,
-                            [],
-                            SlotList),
+    Tab = ets:new(temp_l0, [private, ordered_set]),
+    SlotList = lists:seq(1, Slots),
+    lists:foreach(fun(Slot) ->
+                        Tree = FetchFun(Slot),
+                        L = leveled_skiplist:to_list(Tree),
+                        ets:insert(Tab, L)
+                        end,
+                    SlotList),
+    FullList = ets:tab2list(Tab),
+    true = ets:delete(Tab),
     leveled_log:log_timer("PM002", [length(FullList)], SW),
     FullList.