Remove 8kB read-ahead from couch_file
In production it showed an increased input Erlang IO and increased binary
memory usage.
See attached file in Jira ticket:
COUCHDB-3284
diff --git a/src/couch_file.erl b/src/couch_file.erl
index 2623824..5d11083 100644
--- a/src/couch_file.erl
+++ b/src/couch_file.erl
@@ -20,7 +20,6 @@
-define(INITIAL_WAIT, 60000).
-define(MONITOR_CHECK, 10000).
-define(SIZE_BLOCK, 16#1000). % 4 KiB
--define(READ_AHEAD, 2 * ?SIZE_BLOCK).
-define(IS_OLD_STATE(S), is_pid(S#file.db_monitor)).
-define(PREFIX_SIZE, 5).
-define(DEFAULT_READ_COUNT, 1024).
@@ -423,27 +422,15 @@
{stop, normal, file:close(Fd), File#file{fd = nil}};
handle_call({pread_iolist, Pos}, _From, File) ->
- {RawData, NextPos} = try
- % up to 8Kbs of read ahead
- read_raw_iolist_int(File, Pos, ?READ_AHEAD - (Pos rem ?SIZE_BLOCK))
- catch
- throw:{read_beyond_eof, _} = Reason ->
- throw(Reason);
- throw:{exceed_pread_limit, _, _} = Reason ->
- throw(Reason);
- _:_ ->
- read_raw_iolist_int(File, Pos, 4)
- end,
- <<Prefix:1/integer, Len:31/integer, RestRawData/binary>> =
- iolist_to_binary(RawData),
- case Prefix of
- 1 ->
- {Md5, IoList} = extract_md5(
- maybe_read_more_iolist(RestRawData, 16 + Len, NextPos, File)),
+ {LenIolist, NextPos} = read_raw_iolist_int(File, Pos, 4),
+ case iolist_to_binary(LenIolist) of
+ <<1:1/integer,Len:31/integer>> -> % an MD5-prefixed term
+ {Md5AndIoList, _} = read_raw_iolist_int(File, NextPos, Len+16),
+ {Md5, IoList} = extract_md5(Md5AndIoList),
{reply, {ok, IoList, Md5}, File};
- 0 ->
- IoList = maybe_read_more_iolist(RestRawData, Len, NextPos, File),
- {reply, {ok, IoList, <<>>}, File}
+ <<0:1/integer,Len:31/integer>> ->
+ {Iolist, _} = read_raw_iolist_int(File, NextPos, Len),
+ {reply, {ok, Iolist, <<>>}, File}
end;
handle_call(bytes, _From, #file{fd = Fd} = File) ->
@@ -617,7 +604,7 @@
BlockOffset = Pos rem ?SIZE_BLOCK,
TotalBytes = calculate_total_read_len(BlockOffset, Len),
case Pos + TotalBytes of
- Size when Size > F#file.eof + ?READ_AHEAD ->
+ Size when Size > F#file.eof ->
couch_stats:increment_counter([pread, exceed_eof]),
{_Fd, Filepath} = get(couch_file_fd),
throw({read_beyond_eof, Filepath});