Display TServer clock information in yb-master ui

[kmuthukk]

For debugging purposes, it'll be useful to add a new view say -- http://yb-master:7000/tablet-server-clocks) to visually display the clocks of the various TServers, that provides the following data for each tablet server:

• time since heartbeat (this is already available from the heartbeat sent to master and it is shown here today).
• the physical time on the tserver at the time of heartbeat
• the hybrid time on the tserver at the time of the heartbeat (its physical & logical components).

[kmuthukk]

Implementation pointers on this (based on discussions with @spolitov ):

• add two new fields in TSHeartbeatRequestPB for ts_physical_time and ts_hybrid_time. The plan would be to set these two fields in this function which handles the heartbeats on the TServer side:

  yugabyte-db/src/yb/tserver/heartbeater.cc

  Line 345 in 8bac374

  Status Heartbeater::Thread::TryHeartbeat() {

We typically use fixed64 type for these fields in proto over int64. The latter uses variant length encoding which isn't very useful for very large integer values.

• To obtain the hybrid time on the TServer side, the logic would involve getting the hybrid clock:

auto* hybrid_clock = down_cast<server::HybridClock*>(server_->Clock());

and from there, the current value can be obtained thus:

hybrid_clock->Now().ToUint64()

• To obtain the physical time on the TServer, the TEST_clock() function, currently only used for tests, can be repurposed and renamed to say physical_clock()

yugabyte-db/src/yb/server/hybrid_clock.h

Line 145 in fe4e4cc

const PhysicalClockPtr& TEST_clock() { return clock_; }

and the now timestamp can be obtained via:

Result<PhysicalTime> now = hybrid_clock->physical_clock()->Now();

and subsequently via now->time_point

• On the master side, when heartbeats are received, the new fields in the proto structures can be copied/save into two new fields (for physical & hybrid time) in the TSDescriptor

Here's the master side logic when a TServer heartbeat is received.

yugabyte-db/src/yb/master/master_service.cc

Line 97 in e9e9661

void MasterServiceImpl::TSHeartbeat(const TSHeartbeatRequestPB* req,

These TSDescriptor fields can then be used to drive the UI logic.

[VishnuK007]

I am interested in working on this issue. I will try to submit a patch for it in the next couple of days.

[rkarthik007]

Thanks @VishnuK007! Assigned to you.