fix replication requests exceeding maxRoundWindow + splitting resends#431
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jadalsmail wants to merge 9 commits into
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fix replication requests exceeding maxRoundWindow + splitting resends#431jadalsmail wants to merge 9 commits into
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I also want to review this change before it gets merged so please don't merge it yet
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Can we please have a more descriptive and elaborate PR description? |
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Motivation:
In resendReplicationRequests, timed-out sequences were compressed into contiguous segments and each segment was sent whole to a single node, which can be larger than maxRoundWindow. Thus, nodes drop such requests without responding, so a lagging node would resend the same oversized request forever and never catch up.
initial requests and timed-out retries now share a single send path. A new function, BatchSequences, which distributes seqs as evenly as possible among nodes, returning one batch per node share. Every batch contains at most maxSize sequences.
We also introduce a new variable, MaxRoundRequests, which is the max number of rounds or sequences that fit in one replication request. Every batch is capped at this size by construction. It is set to 10 to match DefaultMaxRoundWindow
Removed: CompressSequences, DistributeSequenceRequests, and the Segment type (plus their tests). the segment/range model they implemented is replaced by batching, and requests may now contain non-contiguous sequences (responders sort incoming requests).
Also, unit test + table tests (for BatchSequences) for testing this functionality were added.