Il 26/11/2015 09:19, Jaime Crespo ha scritto:
> So even if the replicas don't get updated the heartbeat will report
them as up to date?
Not sure exactly what you mean with that. The masters will be updated
continuously every 0.5 seconds (all slaves are read only- no writes
are done there). If replication works, and slaves get updated, that
will mean that they will receive the heartbeat with the same
replication channel than the rest of the updates. If replication
doesn't work, and replicas do not get updated, they will not receive
the heartbeat either, as it comes from replication in order. If
replication stops/fails, heartbeat update will stop (from the slave
perspective), and lag will start to increase from your perspective
(difference between last timestamp written and current time).
This measures the replication lag (aka difference with the master),
not the last time an edit was done by a user, which was what the first
link I sent measured. In other words, if jaimewiki receives only user
edits every hour, heartbeat will still do a write to its master every
half a seconds, thus proving that it is up to date with that
resolution. You can still check the last user edit by checking
recentchanges.
The only reason this could fail (heartbeat updated but wiki not) is if
there was a specific filter denying replication but allowing hearbeat,
only done for specific tables and private wikis. Also the production
master could have a problem, but that would affect the wikis itselves,
not only labs.
To give you an idea of the accuracy of this method, we (will) use it
on production to decide if a slave is usable or not to return
up-to-date data.
For more information on how this works, check
<https://www.percona.com/doc/percona-toolkit/2.1/pt-heartbeat.html#description>
I don't understand, please explain to a 5 years old :-)
_______________________________________________
Labs-l mailing list
[email protected]
https://lists.wikimedia.org/mailman/listinfo/labs-l
