David Ribeiro Alves has posted comments on this change. Change subject: KUDU-798 (part 1) - Unify leader/follower mvcc behavior ......................................................................
Patch Set 6: (1 comment) http://gerrit.cloudera.org:8080/#/c/5055/6//COMMIT_MSG Commit Message: PS6, Line 30: This patch series aims at separating the two concepts and fixing : safe time advancement: : a > I like the general direction here. Not sure about this problem. It's still a subset: all "clean" timestamps are "safe", that is we won't advance clean past safe (otherwise we might get in trouble, like you hinted at) it just that we can't only rely on "clean" to advance when waiting for a repeatable read. For instance say that a follower has a clean timestamp of 5, with no writes going on. The leader then updates the safe time to 10. We can't move "clean" to 10 since another leader might come up with operations that come before that (well not until we have leader leases anyway) so what we do is we advance safe time to 10 and keep clean time where it is. >From another angle, until we have leader leases, safe time might wobble back >and forth, we need to make sure that clean time never does that. so we keep >clean time at the time of the last committed txn. When we have leader leases we can actually trust that safe time won't ever go back but having this separation of concerns is still very useful. For instance the time manager (the safe time keeping entity) is knowledgeable about some consensus information like lag and who the leader is, which we can use to better inform clients on what to do when they try snapshot scans on a replica. -- To view, visit http://gerrit.cloudera.org:8080/5055 To unsubscribe, visit http://gerrit.cloudera.org:8080/settings Gerrit-MessageType: comment Gerrit-Change-Id: I3ba7212f9211f585d4bef00e5ccfc24d5eece224 Gerrit-PatchSet: 6 Gerrit-Project: kudu Gerrit-Branch: master Gerrit-Owner: David Ribeiro Alves <[email protected]> Gerrit-Reviewer: Alexey Serbin <[email protected]> Gerrit-Reviewer: David Ribeiro Alves <[email protected]> Gerrit-Reviewer: Jean-Daniel Cryans <[email protected]> Gerrit-Reviewer: Kudu Jenkins Gerrit-Reviewer: Mike Percy <[email protected]> Gerrit-Reviewer: Tidy Bot Gerrit-Reviewer: Todd Lipcon <[email protected]> Gerrit-HasComments: Yes
