NRG (2.11): Ignore AEs from older terms#5661
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Co-authored-by: Reuben Ninan <reuben@nats.io> Signed-off-by: Neil Twigg <neil@nats.io>
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Many of the follower resets that we see happen because append entries from previous terms can be in-flight during leadership transfers. This problem is worsened when high or variable latency is involved.
When a follower receives an AE from an old term today, they will reset and nuke their WAL and then run a catch-up regardless of the integrity of the log. However this situation ignores the fact that the node might have been otherwise functioning normally and network latency may be worse on some links than others. Silently dropping the AEs from previous terms and restricting the reset behaviour to the last log term and last log index reduces the number of resets considerably whilst maintaining log consistency.
Co-authored-by: Reuben Ninan reuben@nats.io
Signed-off-by: Neil Twigg neil@nats.io