Improve consumer pending count tracking during stream contention #6297
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Signed-off-by: Maurice van Veen <[email protected]>
kozlovic
reviewed
Dec 23, 2024
| // Either we have not reached the message yet, or we've hit the race condition | ||
| // when there is contention at the beginning of the stream. In which case we can | ||
| // only decrement if the ack floor is still low enough to be able to detect it. | ||
| if o.isFilteredMatch(subj) && sseq > o.asflr && (sseq >= o.sseq || !wasPending) { |
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nit: given that o.isFilteredMatch(subj) can be more expensive than the other checks, I would have put it last:
if sseq > o.asflr && (sseq >= o.sseq || !wasPending) && o.isFilteredMatch(subj) {
derekcollison
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Dec 24, 2024
Makes the change suggested in #6297 (comment) Signed-off-by: Maurice van Veen <[email protected]>
derekcollison
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Jan 8, 2025
Reverts the change made in #6297. The change did (somewhat) improve the reliability of the drifting tests if the `o.npc--` was done as a result of contention, but resulted in a regression if `o.npc--` was done twice when a message was acked that did not move the ack floor up for WorkQueue/Interest retention. This PR fixes what would otherwise have been a regression. We really should try to fix the race condition itself though (outside of this PR). Without fixing it the pending count can be incorrect with no way to be resolved unless all messages are consumed, or we'd need to manually recalculate. Signed-off-by: Maurice van Veen <[email protected]>
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The drifting tests would occasionally fail due to the consumer pending count drifting. This was due to a race condition described on
checkNumPending:This PR doesn't fix this race condition, but improves the tracking which improves test reliability. If the race condition happens we can still check if the deleted message is between
o.asflrand theo.sseqthat's skipped ahead. In which case we can still decrement the pending count (o.npc) if the message is not pending/delivered. This improves the reliability of the pending count tracking as long as the ack floor hasn't moved up yet.Signed-off-by: Maurice van Veen [email protected]