[kudu] 01/02: KUDU-2867. Optimize delta timestamp decoding

[al...@apache.org]

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alexey pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/kudu.git

commit 7f7d425eadc10886108a00ee0249d7c3d8372ee0
Author: Todd Lipcon <to...@apache.org>
AuthorDate: Tue Jun 18 00:17:04 2019 -0700

    KUDU-2867. Optimize delta timestamp decoding
    
    When using hybrid clock, all timestamps require a full 8-byte varint to
    be encoded. So, we can inline this fast path in Timestamp::DecodeFrom to
    avoid the more complicated/lengthy GetMemcmpableVarint code.
    
    Change-Id: I1665e0aaed874cf4d47ecf5e467246a9505b0bd1
    Reviewed-on: http://gerrit.cloudera.org:8080/13667
    Tested-by: Kudu Jenkins
    Reviewed-by: Grant Henke <gr...@apache.org>
    Reviewed-by: Alexey Serbin <as...@cloudera.com>
---
 src/kudu/common/timestamp.cc |  5 -----
 src/kudu/common/timestamp.h  | 21 ++++++++++++++++++++-
 2 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/src/kudu/common/timestamp.cc b/src/kudu/common/timestamp.cc
index 1d13d4f..1eed806 100644
--- a/src/kudu/common/timestamp.cc
+++ b/src/kudu/common/timestamp.cc
@@ -21,7 +21,6 @@
 
 #include "kudu/gutil/mathlimits.h"
 #include "kudu/gutil/strings/substitute.h"
-#include "kudu/util/memcmpable_varint.h"
 
 namespace kudu {
 
@@ -30,10 +29,6 @@ const Timestamp Timestamp::kMax(MathLimits<Timestamp::val_type>::kMax);
 const Timestamp Timestamp::kInitialTimestamp(MathLimits<Timestamp::val_type>::kMin + 1);
 const Timestamp Timestamp::kInvalidTimestamp(MathLimits<Timestamp::val_type>::kMax - 1);
 
-bool Timestamp::DecodeFrom(Slice* input) {
-  return GetMemcmpableVarint64(input, &v);
-}
-
 void Timestamp::EncodeTo(faststring* dst) const {
   PutMemcmpableVarint64(dst, v);
 }
diff --git a/src/kudu/common/timestamp.h b/src/kudu/common/timestamp.h
index c9dbad7..7777b64 100644
--- a/src/kudu/common/timestamp.h
+++ b/src/kudu/common/timestamp.h
@@ -22,9 +22,13 @@
 #include <iosfwd>
 #include <string>
 
+#include "kudu/gutil/endian.h"
+#include "kudu/gutil/port.h"
+#include "kudu/util/memcmpable_varint.h"
+#include "kudu/util/slice.h"
+
 namespace kudu {
 class faststring;
-class Slice;
 
 // A transaction timestamp generated by a Clock.
 class Timestamp {
@@ -84,6 +88,21 @@ class Timestamp {
 
 std::ostream& operator<<(std::ostream& o, const Timestamp& timestamp);
 
+inline bool Timestamp::DecodeFrom(Slice* input) {
+  // The most common case is that the timestamp is generated from a
+  // HybridClock, which will always be encoded as an 8-byte varint.
+  // Given this, we can inline fast-path this encoding here and fall
+  // back to GetMemcmpableVarint64 only in the rare case of logical
+  // clocks used in tests.
+  if (PREDICT_TRUE(input->size() >= 9 &&
+      (*input)[0] == 0xff)) {
+    v = BigEndian::Load64(input->data() + 1);
+    input->remove_prefix(9);
+    return true;
+  }
+  return GetMemcmpableVarint64(input, &v);
+}
+
 inline int Timestamp::CompareTo(const Timestamp& other) const {
   if (v < other.v) {
     return -1;