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From kocol...@apache.org
Subject [3/3] chttpd commit: updated refs/heads/2724-chunked-buffering to d4e19ee
Date Tue, 23 Jun 2015 02:01:10 GMT
Buffer rows for normal/longpoll feeds

This patch causses the coordinator to accumulate data in its own buffer
and reduce the number of calls to write data on the socket. The size of
the buffer is configurable:

[httpd]
chunked_response_buffer = 1490

The default is chosen to approximately fill a standard Ethernet frame.

COUCHDB-2724


Project: http://git-wip-us.apache.org/repos/asf/couchdb-chttpd/repo
Commit: http://git-wip-us.apache.org/repos/asf/couchdb-chttpd/commit/d4e19ee7
Tree: http://git-wip-us.apache.org/repos/asf/couchdb-chttpd/tree/d4e19ee7
Diff: http://git-wip-us.apache.org/repos/asf/couchdb-chttpd/diff/d4e19ee7

Branch: refs/heads/2724-chunked-buffering
Commit: d4e19ee78b32e5604f646ae8133e8ad14544f5e5
Parents: f45c8b2
Author: Adam Kocoloski <adam@cloudant.com>
Authored: Mon Jun 22 21:45:26 2015 -0400
Committer: Adam Kocoloski <adam@cloudant.com>
Committed: Mon Jun 22 21:59:41 2015 -0400

----------------------------------------------------------------------
 src/chttpd_db.erl | 45 +++++++++++++++++++++++++++++++++++++--------
 1 file changed, 37 insertions(+), 8 deletions(-)
----------------------------------------------------------------------


http://git-wip-us.apache.org/repos/asf/couchdb-chttpd/blob/d4e19ee7/src/chttpd_db.erl
----------------------------------------------------------------------
diff --git a/src/chttpd_db.erl b/src/chttpd_db.erl
index 71c6cec..84c7084 100644
--- a/src/chttpd_db.erl
+++ b/src/chttpd_db.erl
@@ -40,7 +40,10 @@
     feed,
     mochi,
     prepend = "",
-    responding = false
+    responding = false,
+    buffer = [],
+    bufsize = 0,
+    threshold
 }).
 
 -define(IS_ALL_DOCS(T), (
@@ -83,6 +86,8 @@ handle_changes_req1(#httpd{}=Req, Db) ->
     ChangesArgs = Args0#changes_args{
         filter_fun = couch_changes:configure_filter(Raw, Style, Req, Db)
     },
+    % Default to ~filling the payload of a standard Ethernet frame
+    Max = config:get_integer("httpd", "chunked_response_buffer", 1490),
     case ChangesArgs#changes_args.feed of
     "normal" ->
         T0 = os:timestamp(),
@@ -91,12 +96,21 @@ handle_changes_req1(#httpd{}=Req, Db) ->
         DeltaT = timer:now_diff(os:timestamp(), T0) / 1000,
         couch_stats:update_histogram([couchdb, dbinfo], DeltaT),
         chttpd:etag_respond(Req, Etag, fun() ->
-            Acc0 = #cacc{feed = normal, etag = Etag, mochi = Req},
+            Acc0 = #cacc{
+                feed = normal,
+                etag = Etag,
+                mochi = Req,
+                threshold = Max
+            },
             fabric:changes(Db, fun changes_callback/2, Acc0, ChangesArgs)
         end);
     Feed when Feed =:= "continuous"; Feed =:= "longpoll"; Feed =:= "eventsource"  ->
         couch_stats:increment_counter([couchdb, httpd, clients_requesting_changes]),
-        Acc0 = #cacc{feed = list_to_atom(Feed), mochi = Req},
+        Acc0 = #cacc{
+            feed = list_to_atom(Feed),
+            mochi = Req,
+            threshold = Max
+        },
         try
             fabric:changes(Db, fun changes_callback/2, Acc0, ChangesArgs)
         after
@@ -166,16 +180,17 @@ changes_callback(start, Acc) ->
     {ok, Resp} = chttpd:start_delayed_json_response(Req, 200, [], FirstChunk),
     {ok, Acc#cacc{mochi = Resp, responding = true}};
 changes_callback({change, Change}, Acc) ->
-    #cacc{prepend = Prepend, mochi = Resp} = Acc,
-    {ok, Resp1} = chttpd:send_delayed_chunk(Resp, [Prepend, ?JSON_ENCODE(Change)]),
-    {ok, Acc#cacc{prepend = ",\r\n", mochi = Resp1}};
+    Data = [Acc#cacc.prepend, ?JSON_ENCODE(Change)],
+    Len = iolist_size(Data),
+    maybe_flush_changes_feed(Acc, Data, Len);
 changes_callback({stop, EndSeq, Pending}, Acc) ->
-    #cacc{mochi = Resp} = Acc,
+    #cacc{buffer = Buf, mochi = Resp} = Acc,
     {ok, Resp1} = case is_old_couch(Resp) of
     true ->
-        chttpd:send_delayed_chunk(Resp, "\n],\n\"last_seq\":0}\n");
+        chttpd:send_delayed_chunk(Resp, [Buf | "\n],\n\"last_seq\":0}\n"]);
     false ->
         chttpd:send_delayed_chunk(Resp, [
+            Buf,
             "\n],\n\"last_seq\":",
             ?JSON_ENCODE(EndSeq),
             ",\"pending\":",
@@ -197,6 +212,20 @@ changes_callback({error, Reason}, #cacc{feed = normal, responding = false}
= Acc
 changes_callback({error, Reason}, Acc) ->
     chttpd:send_delayed_error(Acc#cacc.mochi, Reason).
 
+maybe_flush_changes_feed(#cacc{bufsize=Size, threshold=Max} = Acc, Data, Len)
+         when (Size + Len) > Max ->
+    #cacc{buffer = Buffer, mochi = Resp} = Acc,
+    {ok, R1} = chttpd:send_delayed_chunk(Resp, Buffer),
+    {ok, Acc#cacc{prepend = ",\r\n", buffer = Data, bufsize=Len, mochi = R1}};
+maybe_flush_changes_feed(Acc0, Data, Len) ->
+    #cacc{buffer = Buf, bufsize = Size} = Acc0,
+    Acc = Acc0#cacc{
+        prepend = ",\r\n",
+        buffer = [Buf | Data],
+        bufsize = Size + Len
+    },
+    {ok, Acc}.
+
 is_old_couch(Resp) ->
     MochiReq = chttpd:get_delayed_req(Resp),
     case MochiReq:get_header_value("user-agent") of


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