From 16d6daba64852bdff940ea898fd2aafaf1ec6cae Mon Sep 17 00:00:00 2001
From: Avi Kivity <avi@cloudius-systems.com>
Date: Thu, 27 Aug 2015 10:26:33 +0300
Subject: [PATCH] mutation_reader: optimize make_reader_returning()

make_reader_returning() is used by the single-key query path, and is slowed
down by needlessly allocating a vector, which is initialized by copying
the mutation (as initializer_list<> can not be moved from).

Fix by giving it its own implementation instead of relying on
make_reader_returning_many().
---
 mutation_reader.cc | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/mutation_reader.cc b/mutation_reader.cc
index 48d3e18b34..bd75bc4b23 100644
--- a/mutation_reader.cc
+++ b/mutation_reader.cc
@@ -158,7 +158,14 @@ make_lazy_reader(std::function<mutation_reader ()> make_reader) {
 }
 
 mutation_reader make_reader_returning(mutation m) {
-    return make_reader_returning_many({std::move(m)});
+    return [m = std::move(m), done = false] () mutable {
+        if (done) {
+            return make_ready_future<mutation_opt>();
+        } else {
+            done = true;
+            return make_ready_future<mutation_opt>(std::move(m));
+        }
+    };
 }
 
 mutation_reader make_reader_returning_many(std::vector<mutation> mutations) {