Hello Cloud Admins!
As part of
https://phabricator.wikimedia.org/T174569 we have to alter some
big tables.
One of them is logging, which, for instance, in wikidata takes around 8h.
Which is the shard I am currently working on.
Because of the nature of the change (some columns being added) and ROW
based replication (what we use in sanitariums) this change needs to be done
with replication (from sanitarium, or their masters, to the labs servers).
This will obviously generate lag and if not done that way, it will break
replication till the column is added on the labs hosts, and this is less
desirable than replication lag.
I am planning to run the alter probably tomorrow or Monday (I will notify
when I start it) for the sanitarium host in s5, that means that there will
be lag on the labs servers, for a few hours, on the s5 instance (which will
also affect s1 and s3 because we are using the same replication thread for
those shards too - which is a FIXME we have pending).
s2, s4, s6 and s7 will remain unaffected as they have their own replication
thread.
Should you have any questions, let me know!
Thanks
Manuel.