Alexey Serbin has posted comments on this change. ( 
http://gerrit.cloudera.org:8080/15161 )

Change subject: [clock] introduce time source auto selection
......................................................................


Patch Set 6:

(1 comment)

http://gerrit.cloudera.org:8080/#/c/15161/6/src/kudu/clock/hybrid_clock.cc
File src/kudu/clock/hybrid_clock.cc:

http://gerrit.cloudera.org:8080/#/c/15161/6/src/kudu/clock/hybrid_clock.cc@416
PS6, Line 416:         result_builtin_ntp_servers.emplace_back(ntp_server,
             :                                                 
clock::kStandardNtpPort);
> This sounds reasonable.  I'll set the default value for the glfag then.  Th
After taking a closer look, I think passing around the auto-detected servers is 
safer in this case.

If controlling the set of servers for the built-in NTP client using the flags, 
it would be necessary to set default values for the following flags:
  * --builtin_ntp_servers
  * --builtin_ntp_client_enable_auto_config_in_cloud

As I understand, the idea is to (a) set the default value for 
--builtin_ntp_servers using the set of the servers found at the time of 
auto-selecting the time source, and (b) set the default value for 
--builtin_ntp_client_enable_auto_config_in_cloud to 'false' to avoid doing the 
same work twice.  However, if the value for flag in (b) has been explicitly set 
to 'true', setting the default value for the flag to 'false' wouldn't help to 
avoid running the auto-detection of the NTP servers again in 
BuiltInNtp::InitImpl().

I also thought of getting rid of the 
--builtin_ntp_client_enable_auto_config_in_cloud flag and using the special 
value (an empty string) for --builtin_ntp_servers.  However, if going that 
route, it would prevent us from using the custom set of NTP servers to fallback 
if the auto-configuration fails.

So, I think I'll keep the approach of passing the auto-detected NTP servers 
around.

What do you think?



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Gerrit-Project: kudu
Gerrit-Branch: master
Gerrit-MessageType: comment
Gerrit-Change-Id: If9f2bc94f4a1ad32fe365d4f6f0707913fb476a4
Gerrit-Change-Number: 15161
Gerrit-PatchSet: 6
Gerrit-Owner: Alexey Serbin <[email protected]>
Gerrit-Reviewer: Adar Dembo <[email protected]>
Gerrit-Reviewer: Alexey Serbin <[email protected]>
Gerrit-Reviewer: Grant Henke <[email protected]>
Gerrit-Reviewer: Kudu Jenkins (120)
Gerrit-Reviewer: Tidy Bot (241)
Gerrit-Reviewer: Volodymyr Verovkin <[email protected]>
Gerrit-Comment-Date: Wed, 12 Feb 2020 00:05:30 +0000
Gerrit-HasComments: Yes

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