From 25b4099eeca34bd8d301b594440d56f20ad813f4 Mon Sep 17 00:00:00 2001
From: Kresten Krab Thorup <krab@trifork.com>
Date: Mon, 23 Apr 2012 04:23:52 +0200
Subject: [PATCH] Only compress if compressed size is smaller

---
 src/hanoi_util.erl   | 21 ++++++++++++++-------
 src/hanoi_writer.erl |  7 ++++++-
 2 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/src/hanoi_util.erl b/src/hanoi_util.erl
index 5bcbe95..ba8e4c0 100644
--- a/src/hanoi_util.erl
+++ b/src/hanoi_util.erl
@@ -49,23 +49,30 @@ estimate_node_size_increment(_KVList,Key,Value) ->
 -define(SNAPPY_COMPRESSION, 1).
 -define(GZIP_COMPRESSION, 2).
 
-encode_index_node(Level, KVList, Compress) ->
+encode_index_node(KVList, Compress) ->
 
     TermData = erlang:term_to_binary(KVList),
 
     case Compress of
         snappy ->
             {ok, Snappied} = snappy:compress(TermData),
-            CompressedData = [?SNAPPY_COMPRESSION|Snappied];
+            if byte_size(Snappied) > byte_size(TermData) ->
+                    OutData = [?NO_COMPRESSION|TermData];
+               true ->
+                    OutData = [?SNAPPY_COMPRESSION|Snappied]
+            end;
         gzip ->
-            CompressedData = [?GZIP_COMPRESSION|zlib:gzip(TermData)];
+            GZipData = zlib:gzip(TermData);
+            if byte_size(GZipData) > byte_size(TermData) ->
+                    OutData = [?NO_COMPRESSION|TermData];
+               true ->
+                    OutData = [?GZIP_COMPRESSION|GZipData]
+            end;
         _ ->
-            CompressedData = [?NO_COMPRESSION|TermData]
+            OutData = [?NO_COMPRESSION|TermData]
     end,
 
-    Size = erlang:iolist_size(CompressedData),
-
-    {ok, Size+6, [ <<(Size+2):32/unsigned, Level:16/unsigned>> | CompressedData ] }.
+    {ok, OutData}.
 
 decode_index_node(Level, <<Tag, Data/binary>>) ->
 
diff --git a/src/hanoi_writer.erl b/src/hanoi_writer.erl
index 131a146..50e6bea 100644
--- a/src/hanoi_writer.erl
+++ b/src/hanoi_writer.erl
@@ -187,8 +187,13 @@ add_record(Level, Key, Value, #state{ nodes=Nodes }=State) ->
 
 close_node(#state{nodes=[#node{ level=Level, members=NodeMembers }|RestNodes], compress=Compress} = State) ->
     OrderedMembers = lists:reverse(NodeMembers),
-    {ok, DataSize, Data} = hanoi_util:encode_index_node(Level, OrderedMembers, Compress),
+    {ok, BlockData} = hanoi_util:encode_index_node(OrderedMembers, Compress),
     NodePos = State#state.index_file_pos,
+
+    BlockSize = byte_size(BlockData),
+    Data = [ <<(BlockSize+2):32/unsigned, Level:16/unsigned>> | BlockData ],
+    DataSize = BlockData + 6,
+
     ok = file:write(State#state.index_file, Data),
 
     {FirstKey, _} = hd(OrderedMembers),