[kudu] 02/02: [clock] add exponential backoff in HybridClock::Init()

[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 1bb267bd8587473c567ca76426689e33ff4c9b89
Author: Alexey Serbin <al...@apache.org>
AuthorDate: Wed Oct 16 15:18:49 2019 -0700

    [clock] add exponential backoff in HybridClock::Init()
    
    This patch introduces exponential back-off when polling the
    synchronisation status of the underlying time service (i.e. calling
    TimeService::WalltimeWithError()) during HybridClock::Init().  Now,
    the polling interval starts with 1 millisecond and exponentially grows
    up to 1 second.
    
    Prior to this patch, the polling interval was one second, and in case
    if time source synchronized faster than in one second,
    HybridClock::Init() would incur extra latency (e.g., in case of tests
    running with the built-in NTP client synchronized against MiniChronyd).
    
    I verified that with the new approach ExternalMiniCluster-based tests
    run faster:
    
      before
        [       OK ] AllTypesItest/9.TestTimestampPadding (6794 ms)
    
      after
        [       OK ] AllTypesItest/9.TestTimestampPadding (2730 ms)
    
    Change-Id: I75924f1fdcf6a32684cda29bbfa959b00172b50e
    Reviewed-on: http://gerrit.cloudera.org:8080/14472
    Reviewed-by: Adar Dembo <ad...@cloudera.com>
    Tested-by: Kudu Jenkins
---
 src/kudu/clock/hybrid_clock.cc | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/kudu/clock/hybrid_clock.cc b/src/kudu/clock/hybrid_clock.cc
index 07170f6..99ea277 100644
--- a/src/kudu/clock/hybrid_clock.cc
+++ b/src/kudu/clock/hybrid_clock.cc
@@ -151,6 +151,7 @@ Status HybridClock::Init() {
   Status s;
   uint64_t now_usec;
   uint64_t error_usec;
+  int poll_backoff_ms = 1;
   do {
     s = time_service_->WalltimeWithError(&now_usec, &error_usec);
     if (!s.IsServiceUnavailable()) {
@@ -168,7 +169,8 @@ Status HybridClock::Init() {
       }
       need_log = false;
     }
-    SleepFor(MonoDelta::FromSeconds(1));
+    SleepFor(MonoDelta::FromMilliseconds(poll_backoff_ms));
+    poll_backoff_ms = std::min(2 * poll_backoff_ms, 1000);
   } while (MonoTime::Now() < deadline);
 
   if (!s.ok()) {