testdata: add a lagging commit test #137
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@nvanbenschoten @ahrtr PTAL. This is a regression test for potential future fixes for #138. |
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This commit adds a test demonstrating the effect of delayed commit on a follower node after a network hiccup between the leader and this follower. In the described scenario, after the moment of committing an entry on the leader, it takes HeartbeatInterval + 3/2 * RTT until the follower learns this entry is committed. This is suboptimal, and could take HeartbeatInverval + 1/2 * RTT if the leader didn't cut the commit index at Progress.Match before sending it to the follower. Signed-off-by: Pavel Kalinnikov <[email protected]>
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Why do we care? Follower reads? |
Yes, and also the general "convergence" of the system (resulting in fewer messages etc). For other kinds of reads, like quorum reads, this also seems relevant. |
erikgrinaker
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@ahrtr Good to merge? |
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This commit adds a test demonstrating the effect of delayed commit on a follower node after a network hiccup between the leader and this follower.
In the described scenario, after the moment of committing an entry on the leader, it takes
HeartbeatInterval + 3/2 * RTTuntil the follower learns this entry is committed.This is suboptimal, and could take
HeartbeatInverval + 1/2 * RTTif the leader didn't cut the commit index atProgress.Matchbefore sending it to the follower.Informs #138