David Ribeiro Alves has posted comments on this change. ( 
http://gerrit.cloudera.org:8080/8133 )

Change subject: [tablet copy] end session before bootstrapping tablet
......................................................................


Patch Set 1:

My understanding of it is the following. I would recommend that would browse 
the code to make sure this is still the case.

because by the time the tablet boopststraps the leader might have ended up 
deleting all the logs that it needs to catch up to the leader.
- say that you have wal segments 0-10 when tablet copy starts
- tablet copy will anchor 0 until its destroyed, meaning the source wont delete 
it
- when tablet copy is done the tablet still needs to boostrap which will take 
some time.
- when tablet bootstrap is done the replica will need to continue catching up 
to the leader, this time through consensus. It needs segment 11 to be still 
available.

We need the anchor to still be alive at this point, otherwise theres nothing 
preventing the leader from anchoring segment 11 and thus making the new replica 
unable to catch up.

True that we're not optimal, we're anchoring 0 and we might only need to anchor 
10/11 but no anchor at all is likely to cause replicas to start to fail copying.


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Gerrit-Project: kudu
Gerrit-Branch: master
Gerrit-MessageType: comment
Gerrit-Change-Id: I20592007a40113d8409f121b226bcccca14e8300
Gerrit-Change-Number: 8133
Gerrit-PatchSet: 1
Gerrit-Owner: Alexey Serbin <[email protected]>
Gerrit-Reviewer: Alexey Serbin <[email protected]>
Gerrit-Reviewer: David Ribeiro Alves <[email protected]>
Gerrit-Reviewer: Kudu Jenkins
Gerrit-Reviewer: Mike Percy <[email protected]>
Gerrit-Comment-Date: Mon, 25 Sep 2017 20:21:33 +0000
Gerrit-HasComments: No

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