vreplication: improved lag tracking #4637
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The new lag tracking introduces the following changes: * VStreamer sends its current time along with every event. This allows for VPlayer to correct for any clock skew that may exist between the two machines. This results in a more accurate calculation of lag. * If there are no events to send for a period of time, VStreamer sends a heartbeat event. This allows us VPlayer to essentially know for sure that it's still caught up. * If VPlayer receives no event for its wait period, then it updates the SecondsBehindMaster stat to indicate that it's actually falling behind. The VStreamer timeout for heartbeat is set slightly lower than the VPlayer idle timeout. This ensures that Vplayer won't timeout exactly when it's about to receive the heartbeat event. Signed-off-by: Sugu Sougoumarane <ssougou@gmail.com>
Signed-off-by: Sugu Sougoumarane <ssougou@gmail.com>
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@sougou and I talked about this PR in Slack. I suggested we add some comments to make some parts clearer to future readers. This was addressed. LGTM. |
rafael
approved these changes
Mar 3, 2019
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Failure doesn't look related to PR (vtctld_web has flaked a few times before). Going to override and merge. |
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The new lag tracking introduces the following changes:
allows for VPlayer to correct for any clock skew that may
exist between the two machines. This results in a more accurate
calculation of lag.
sends a heartbeat event. This allows us VPlayer to essentially
know for sure that it's still caught up.
the SecondsBehindMaster stat to indicate that it's actually falling
behind.
The VStreamer timeout for heartbeat is set slightly lower than the
VPlayer idle timeout. This ensures that Vplayer won't timeout
exactly when it's about to receive the heartbeat event.
Signed-off-by: Sugu Sougoumarane ssougou@gmail.com