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https://issues.apache.org/jira/browse/RATIS-352?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16691272#comment-16691272
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Jitendra Nath Pandey commented on RATIS-352:
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The patch looks ok to me. Just want to mention a couple of considerations:
# Should we flush the metadata entry before updating the watch request?
** The patch doesn't do that, and I agree it is ok, because watch requests
wait for followers to respond, and for majority commit, leader waits for
applying transaction.
# Does the follower update its commitIndex, only after flushing the commit
metadata entry?
** It seems this is important, so that when leader learns the commitInfo from
followers, the commitIndex is persisted in followers. This is not obvious from
this patch, hence the question.
> Persist commit index in Raft log.
> ---------------------------------
>
> Key: RATIS-352
> URL: https://issues.apache.org/jira/browse/RATIS-352
> Project: Ratis
> Issue Type: Improvement
> Components: server
> Reporter: Tsz Wo Nicholas Sze
> Assignee: Tsz Wo Nicholas Sze
> Priority: Major
> Attachments: r352_20181106.patch, r352_20181107.patch,
> r352_20181115.patch, r352_20181117.patch, r352_20181117b.patch,
> r352_20181118.patch
>
>
> Current the commit index is not persisted in the Raft log. When a server
> restarts, it cannot apply its log until it has joined a Raft group. There is
> no problem if there is a Raft group.
> However, a server cannot recover its data when formatting a Raft group is
> impossible (e.g. a majority of servers are dead). Ideally, a server can
> safely apply the log up to the commit index. The JIRA is to persist the
> commit index so that such recovery is possible.
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