change guid to a binary, using the md5 of term_to_binary

The main motivation is to reduce the memory and on-disk footprint of
the guid from ~34 bytes to 16. But it turns out that this actually
results in a speed improvement of a few percent as well, even for
non-persistent messaging, presumably due to the memory management
effects and the fact that 16 byte binaries are easier to copy between
processes than the deep(ish) original guid structure.

5 files changed, 44 insertions, 39 deletions

diff --git a/include/rabbit.hrl b/include/rabbit.hrl
index c17ac7eb..095044e7 100644
--- a/include/rabbit.hrl
+++ b/include/rabbit.hrl
@@ -89,7 +89,7 @@
 -type(file_open_mode() :: any()).
 
 %% this is really an abstract type, but dialyzer does not support them
--type(guid() :: any()).
+-type(guid() :: binary()).
 -type(txn() :: guid()).
 -type(pkey() :: guid()).
 -type(r(Kind) ::
diff --git a/src/rabbit_guid.erl b/src/rabbit_guid.erl
index 45816b85..5053d188 100644
--- a/src/rabbit_guid.erl
+++ b/src/rabbit_guid.erl
@@ -99,7 +99,7 @@ guid() ->
             {S, I}   -> {S, I+1}
         end,
     put(guid, G),
-    G.
+    erlang:md5(term_to_binary(G)).
 
 %% generate a readable string representation of a guid. Note that any
 %% monotonicity of the guid is not preserved in the encoding.
@@ -110,7 +110,7 @@ string_guid(Prefix) ->
     %%
     %% TODO: once debian stable and EPEL have moved from R11B-2 to
     %% R11B-4 or later we should change this to use base64.
-    Prefix ++ "-" ++ ssl_base64:encode(erlang:md5(term_to_binary(guid()))).
+    Prefix ++ "-" ++ ssl_base64:encode(guid()).
 
 binstring_guid(Prefix) ->
     list_to_binary(string_guid(Prefix)).
diff --git a/src/rabbit_msg_file.erl b/src/rabbit_msg_file.erl
index f14656cf..46128612 100644
--- a/src/rabbit_msg_file.erl
+++ b/src/rabbit_msg_file.erl
@@ -46,7 +46,7 @@
 -ifdef(use_specs).
 
 -type(io_device() :: any()).
--type(msg_id() :: any()).
+-type(msg_id() :: binary()).
 -type(msg() :: any()).
 -type(msg_attrs() :: any()).
 -type(position() :: non_neg_integer()).
@@ -63,16 +63,16 @@
 
 %%----------------------------------------------------------------------------
 
-append(FileHdl, MsgId, MsgBody, MsgAttrs) ->
-    [MsgIdBin, MsgBodyBin, MsgAttrsBin] = Bins =
-        [term_to_binary(X) || X <- [MsgId, MsgBody, MsgAttrs]],
-    [MsgIdBinSize, MsgBodyBinSize, MsgAttrsBinSize] = Sizes =
-        [size(B) || B <- Bins],
+append(FileHdl, MsgId, MsgBody, MsgAttrs) when is_binary(MsgId) ->
+    MsgBodyBin  = term_to_binary(MsgBody),
+    MsgAttrsBin = term_to_binary(MsgAttrs),
+    [MsgIdSize, MsgBodyBinSize, MsgAttrsBinSize] = Sizes =
+        [size(B) || B <- [MsgId, MsgBodyBin, MsgAttrsBin]],
     Size = lists:sum(Sizes),
     case file:write(FileHdl, <<Size:?INTEGER_SIZE_BITS,
-                               MsgIdBinSize:?INTEGER_SIZE_BITS,
+                               MsgIdSize:?INTEGER_SIZE_BITS,
                                MsgAttrsBinSize:?INTEGER_SIZE_BITS,
-                               MsgIdBin:MsgIdBinSize/binary,
+                               MsgId:MsgIdSize/binary,
                                MsgAttrsBin:MsgAttrsBinSize/binary,
                                MsgBodyBin:MsgBodyBinSize/binary,
                                ?WRITE_OK_MARKER:?WRITE_OK_SIZE_BITS>>) of
@@ -85,17 +85,16 @@ read(FileHdl, TotalSize) ->
     SizeWriteOkBytes = Size + 1,
     case file:read(FileHdl, TotalSize) of
         {ok, <<Size:?INTEGER_SIZE_BITS,
-               MsgIdBinSize:?INTEGER_SIZE_BITS,
+               MsgIdSize:?INTEGER_SIZE_BITS,
                MsgAttrsBinSize:?INTEGER_SIZE_BITS,
                Rest:SizeWriteOkBytes/binary>>} ->
-            BodyBinSize = Size - MsgIdBinSize - MsgAttrsBinSize,
-            <<MsgIdBin:MsgIdBinSize/binary,
+            BodyBinSize = Size - MsgIdSize - MsgAttrsBinSize,
+            <<MsgId:MsgIdSize/binary,
               MsgAttrsBin:MsgAttrsBinSize/binary,
               MsgBodyBin:BodyBinSize/binary,
               ?WRITE_OK_MARKER:?WRITE_OK_SIZE_BITS>> = Rest,
-            [MsgId, MsgBody, MsgAttrs] =
-                [binary_to_term(B) || B <- [MsgIdBin, MsgBodyBin, MsgAttrsBin]],
-            {ok, {MsgId, MsgBody, MsgAttrs}};
+            {ok, {MsgId,
+                  binary_to_term(MsgBodyBin), binary_to_term(MsgAttrsBin)}};
         KO -> KO
     end.
 
@@ -119,10 +118,10 @@ read_next(FileHdl, Offset) ->
     case file:read(FileHdl, ThreeIntegers) of
         {ok,
          <<Size:?INTEGER_SIZE_BITS,
-           MsgIdBinSize:?INTEGER_SIZE_BITS,
+           MsgIdSize:?INTEGER_SIZE_BITS,
            MsgAttrsBinSize:?INTEGER_SIZE_BITS>>} ->
             if Size == 0 -> eof; %% Nothing we can do other than stop
-               MsgIdBinSize == 0 orelse MsgAttrsBinSize == 0 ->
+               MsgIdSize == 0 orelse MsgAttrsBinSize == 0 ->
                     %% current message corrupted, try skipping past it
                     ExpectedAbsPos = Offset + Size + ?FILE_PACKING_ADJUSTMENT,
                     case file:position(FileHdl, {cur, Size + 1}) of
@@ -131,9 +130,9 @@ read_next(FileHdl, Offset) ->
                         KO                   -> KO
                     end;
                true -> %% all good, let's continue
-                    HeaderSize = MsgIdBinSize + MsgAttrsBinSize,
+                    HeaderSize = MsgIdSize + MsgAttrsBinSize,
                     case file:read(FileHdl, HeaderSize) of
-                        {ok, <<MsgIdBin:MsgIdBinSize/binary,
+                        {ok, <<MsgId:MsgIdSize/binary,
                                MsgAttrsBin:MsgAttrsBinSize/binary>>} ->
                             TotalSize = Size + ?FILE_PACKING_ADJUSTMENT,
                             ExpectedAbsPos = Offset + TotalSize - 1,
@@ -144,7 +143,7 @@ read_next(FileHdl, Offset) ->
                                     case file:read(FileHdl, 1) of
                                         {ok, <<?WRITE_OK_MARKER:
                                                ?WRITE_OK_SIZE_BITS>>} ->
-                                            {ok, {binary_to_term(MsgIdBin),
+                                            {ok, {MsgId,
                                                   binary_to_term(MsgAttrsBin),
                                                   TotalSize, NextOffset}};
                                         {ok, _SomeOtherData} ->
diff --git a/src/rabbit_msg_store.erl b/src/rabbit_msg_store.erl
index 357c4867..da904193 100644
--- a/src/rabbit_msg_store.erl
+++ b/src/rabbit_msg_store.erl
@@ -82,7 +82,7 @@
 -type(mode() :: 'ram_disk' | 'disk_only').
 -type(dets_table() :: any()).
 -type(ets_table() :: any()).
--type(msg_id() :: any()).
+-type(msg_id() :: binary()).
 -type(msg() :: any()).
 -type(msg_attrs() :: any()).
 -type(file_path() :: any()).
diff --git a/src/rabbit_tests.erl b/src/rabbit_tests.erl
index 039e9aa4..1f2187bc 100644
--- a/src/rabbit_tests.erl
+++ b/src/rabbit_tests.erl
@@ -848,8 +848,11 @@ benchmark_disk_queue() ->
     passed.
 
 rdq_message(MsgId, MsgBody, IsPersistent) ->
-    rabbit_basic:message(x, <<>>, [], MsgBody, MsgId, IsPersistent).
+    rabbit_basic:message(x, <<>>, [], MsgBody, term_to_binary(MsgId),
+                         IsPersistent).
 
+rdq_match_message(Msg, MsgId, MsgBody, Size) when is_number(MsgId) ->
+    rdq_match_message(Msg, term_to_binary(MsgId), MsgBody, Size);
 rdq_match_message(
   #basic_message { guid = MsgId, content =
                    #content { payload_fragments_rev = [MsgBody] }},
@@ -860,13 +863,17 @@ rdq_match_messages(#basic_message { guid = MsgId, content = #content { payload_f
                    #basic_message { guid = MsgId, content = #content { payload_fragments_rev = MsgBody }}) ->
     ok.
 
+commit_list(List, MsgCount) ->
+    lists:zip([term_to_binary(MsgId) || MsgId <- List],
+              lists:duplicate(MsgCount, false)).
+
 rdq_time_tx_publish_commit_deliver_ack(Qs, MsgCount, MsgSizeBytes) ->
     Startup = rdq_virgin(),
     rdq_start(),
     QCount = length(Qs),
     Msg = <<0:(8*MsgSizeBytes)>>,
     List = lists:seq(1, MsgCount),
-    CommitList = lists:zip(List, lists:duplicate(MsgCount, false)),
+    CommitList = commit_list(List, MsgCount),
     {Publish, ok} =
         timer:tc(?MODULE, rdq_time_commands,
                  [[fun() -> [rabbit_disk_queue:tx_publish(rdq_message(N, Msg, false))
@@ -905,7 +912,7 @@ rdq_stress_gc(MsgCount) ->
     MsgSizeBytes = 256*1024,
     Msg = <<0:(8*MsgSizeBytes)>>, % 256KB
     List = lists:seq(1, MsgCount),
-    CommitList = lists:zip(List, lists:duplicate(MsgCount, false)),
+    CommitList = commit_list(List, MsgCount),
     [rabbit_disk_queue:tx_publish(rdq_message(N, Msg, false)) || N <- List],
     rabbit_disk_queue:tx_commit(q, CommitList, []),
     StartChunk = round(MsgCount / 20), % 5%
@@ -948,7 +955,7 @@ rdq_test_startup_with_queue_gaps() ->
     Total = 1000,
     Half = round(Total/2),
     All = lists:seq(1,Total),
-    CommitAll = lists:zip(All, lists:duplicate(Total, false)),
+    CommitAll = commit_list(All, Total),
     [rabbit_disk_queue:tx_publish(rdq_message(N, Msg, true)) || N <- All],
     rabbit_disk_queue:tx_commit(q, CommitAll, []),
     io:format("Publish done~n", []),
@@ -1005,7 +1012,7 @@ rdq_test_redeliver() ->
     Total = 1000,
     Half = round(Total/2),
     All = lists:seq(1,Total),
-    CommitAll = lists:zip(All, lists:duplicate(Total, false)),
+    CommitAll = commit_list(All, Total),
     [rabbit_disk_queue:tx_publish(rdq_message(N, Msg, false)) || N <- All],
     rabbit_disk_queue:tx_commit(q, CommitAll, []),
     io:format("Publish done~n", []),
@@ -1058,7 +1065,7 @@ rdq_test_purge() ->
     Total = 1000,
     Half = round(Total/2),
     All = lists:seq(1,Total),
-    CommitAll = lists:zip(All, lists:duplicate(Total, false)),
+    CommitAll = commit_list(All, Total),
     [rabbit_disk_queue:tx_publish(rdq_message(N, Msg, false)) || N <- All],
     rabbit_disk_queue:tx_commit(q, CommitAll, []),
     io:format("Publish done~n", []),
@@ -1170,12 +1177,10 @@ rdq_test_mixed_queue_modes() ->
 rdq_test_mode_conversion_mid_txn() ->
     Payload = <<0:(8*256)>>,
     MsgIdsA = lists:seq(0,9),
-    MsgsA = [ rabbit_basic:message(x, <<>>, [], Payload, MsgId,
-                                   (0 == MsgId rem 2))
-            || MsgId <- MsgIdsA ],
+    MsgsA = [ rdq_message(MsgId, Payload, (0 == MsgId rem 2))
+              || MsgId <- MsgIdsA ],
     MsgIdsB = lists:seq(10,20),
-    MsgsB = [ rabbit_basic:message(x, <<>>, [], Payload, MsgId,
-                                   (0 == MsgId rem 2))
+    MsgsB = [ rdq_message(MsgId, Payload, (0 == MsgId rem 2))
             || MsgId <- MsgIdsB ],
 
     rdq_virgin(),
@@ -1229,7 +1234,8 @@ rdq_tx_publish_mixed_alter_commit_get(MS0, MsgsA, MsgsB, Mode, CommitOrCancel) -
                 {AckTags, MS8} =
                     lists:foldl(
                       fun (Msg, {Acc, MS7}) ->
-                              Rem = Len1 - (Msg #basic_message.guid) - 1,
+                              MsgId = binary_to_term(Msg #basic_message.guid),
+                              Rem = Len1 - MsgId - 1,
                               {{Msg1, false, AckTag, Rem}, MS7a} =
                                   rabbit_mixed_queue:fetch(MS7),
                               ok = rdq_match_messages(Msg, Msg1),
@@ -1243,7 +1249,8 @@ rdq_tx_publish_mixed_alter_commit_get(MS0, MsgsA, MsgsB, Mode, CommitOrCancel) -
                 {AckTags, MS8} =
                     lists:foldl(
                       fun (Msg, {Acc, MS7}) ->
-                              Rem = Len0 - (Msg #basic_message.guid) - 1,
+                              MsgId = binary_to_term(Msg #basic_message.guid),
+                              Rem = Len0 - MsgId - 1,
                               {{Msg1, false, AckTag, Rem}, MS7a} =
                                   rabbit_mixed_queue:fetch(MS7),
                               ok = rdq_match_messages(Msg, Msg1),
@@ -1266,9 +1273,8 @@ rdq_test_disk_queue_modes() ->
     Total = 1000,
     Half1 = lists:seq(1,round(Total/2)),
     Half2 = lists:seq(1 + round(Total/2), Total),
-    CommitHalf1 = lists:zip(Half1, lists:duplicate(round(Total/2), false)),
-    CommitHalf2 = lists:zip(Half2, lists:duplicate
-                            (Total - round(Total/2), false)),
+    CommitHalf1 = commit_list(Half1, round(Total/2)),
+    CommitHalf2 = commit_list(Half2, Total - round(Total/2)),
     [rabbit_disk_queue:tx_publish(rdq_message(N, Msg, false)) || N <- Half1],
     ok = rabbit_disk_queue:tx_commit(q, CommitHalf1, []),
     io:format("Publish done~n", []),