From 961d81a01f9f5f8f3c6807f143ba0678c14c4a28 Mon Sep 17 00:00:00 2001
From: Filipe David Borba Manana <fdmanana@apache.org>
Date: Wed, 10 Nov 2010 21:14:00 +0000
Subject: Micro optimization: faster header reads (read the whole block at
 once, so far headers are always smaller than a block). Read time is basically
 reduced to half.

git-svn-id: https://svn.apache.org/repos/asf/couchdb/trunk@1033714 13f79535-47bb-0310-9956-ffa450edef68
---
 src/couchdb/couch_file.erl | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/src/couchdb/couch_file.erl b/src/couchdb/couch_file.erl
index 860c9f4e..a3a728c7 100644
--- a/src/couchdb/couch_file.erl
+++ b/src/couchdb/couch_file.erl
@@ -486,11 +486,18 @@ find_header(Fd, Block) ->
     end.
 
 load_header(Fd, Block) ->
-    {ok, <<1>>} = file:pread(Fd, Block*?SIZE_BLOCK, 1),
-    {ok, <<HeaderLen:32/integer>>} = file:pread(Fd, (Block*?SIZE_BLOCK) + 1, 4),
+    {ok, <<1, HeaderLen:32/integer, RestBlock/binary>>} =
+        file:pread(Fd, Block * ?SIZE_BLOCK, ?SIZE_BLOCK),
     TotalBytes = calculate_total_read_len(1, HeaderLen),
-    {ok, <<RawBin:TotalBytes/binary>>} =
-            file:pread(Fd, (Block*?SIZE_BLOCK) + 5, TotalBytes),
+    case TotalBytes > byte_size(RestBlock) of
+    false ->
+        <<RawBin:TotalBytes/binary, _/binary>> = RestBlock;
+    true ->
+        {ok, Missing} = file:pread(
+            Fd, (Block * ?SIZE_BLOCK) + 5 + byte_size(RestBlock),
+            TotalBytes - byte_size(RestBlock)),
+        RawBin = <<RestBlock/binary, Missing/binary>>
+    end,
     <<Md5Sig:16/binary, HeaderBin/binary>> =
         iolist_to_binary(remove_block_prefixes(1, RawBin)),
     Md5Sig = couch_util:md5(HeaderBin),
-- 
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