tracker: clean-up Match, Next and MaybeUpdate #165
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@ahrtr PTAL |
| Match: 0, | ||
| Next: max(c.LastIndex, 1), // invariant: Match < Next |
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Why the Next is set to lastIndex + 1 in reset? Should we make them consistent?
Line 784 in 83d8dec
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I tried c.LastIndex + 1 here for consistency, but it breaks a few tests. I think the reason is: setting to lastIndex + 1 precludes sending a MsgApp message instantly (the maybeSendAppend treats it as "everything is in flight", and won't send any appends until there is a heartbeat reply). So, here we set it to LastIndex to guarantee at least one message send. Also, typically this last entry contains the very config change that we're performing here.
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setting to lastIndex + 1 precludes sending a MsgApp message instantly
Makes sense.
tracker/progress.go
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| @@ -115,17 +123,17 @@ func (pr *Progress) BecomeProbe() { | |||
| if pr.State == StateSnapshot { | |||
| pendingSnapshot := pr.PendingSnapshot | |||
| pr.ResetState(StateProbe) | |||
| pr.Next = max(pr.Match+1, pendingSnapshot+1) | |||
| pr.Next = max(pr.Match+1, pendingSnapshot+1) // invariant: Match < Next | |||
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I see there are comments "// invariant: Match < Next" in multiple places. I think we only need to keep the comment in type Progress struct, and also add verification (I was planning to do it for a while) to safeguard it instead of adding comment everywhere.
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Removed the comment from all the places, except the non-trivial max(c.LastIndex, 1) in one place (where this invariant was not maintained before this PR). It should be ok to have comments like this though, IMO, esp. while the invariant is not checked explicitly at the moment.
This commit documents the meaning of Match and Next field in the Progress struct. It also ensures that the invariant is maintained in all code places that initialize or modify these fields. Signed-off-by: Pavel Kalinnikov <[email protected]>
The Progress.MaybeUpdate is only needed on the leader. In the raft.restore() method, the state is either Follower or Candidate. Non-leader states don't have a replication flow, and don't need to track Match/Next index. Signed-off-by: Pavel Kalinnikov <[email protected]>
Signed-off-by: Pavel Kalinnikov <[email protected]>
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I won't have time to look at this until next week. |
This PR documents the meaning of
MatchandNextfield in theProgressstruct. It also ensures that theMatch < Nextinvariant is maintained in all code places that initialize or modify these fields.It then simplifies the
Progress.MaybeUpdatemethod, given that the invariant is true before it is invoked.