Improved handling of truncation with ACKS=1 #16475
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mmaslankaprv
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bharathv
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Feb 5, 2024
| @@ -2013,7 +2013,7 @@ consensus::do_append_entries(append_entries_request&& r) { | |||
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| // section 3 | |||
| if (request_metadata.prev_log_index < last_log_offset) { | |||
| if (unlikely(request_metadata.prev_log_index < _commit_index)) { | |||
| if (unlikely(request_metadata.prev_log_index < last_visible_index())) { | |||
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so IIUC the problem is with follower fetching + acks=1 because, on a follower the log can be truncated below high watermark (because of committed offset check) say during recovery and the subsequent read from the follower may result in an out of range read, is that correct?
mmaslankaprv
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ztlpn
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| @@ -2013,7 +2013,7 @@ consensus::do_append_entries(append_entries_request&& r) { | |||
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| // section 3 | |||
| if (request_metadata.prev_log_index < last_log_offset) { | |||
| if (unlikely(request_metadata.prev_log_index < _commit_index)) { | |||
| if (unlikely(request_metadata.prev_log_index < last_visible_index())) { | |||
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Should we use last_visible_index() in line 2020 as well? (not entirely understanding its significance, but seems logical...)
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makes sense, i will change this
Signed-off-by: Michal Maslanka <michal@redpanda.com>
If an offset was already visible a follower must not be allowed to truncate it as it may lead to a situation in which an offset is visible and not readable. Visible batches has the same replication guarantees as committed batches as leader still waits for the majority to acknowledge message at given offset before making it visible to the readers. This makes it possible not to truncate offsets which were previously visible. Signed-off-by: Michal Maslanka <michal@redpanda.com>
Added test checking if an offset that is visible on the leader is not truncated on the followers. Signed-off-by: Michal Maslanka <michal@redpanda.com>
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ztlpn
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Feb 7, 2024
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/backport v23.3.x |
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/backport v23.2.x |
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Failed to create a backport PR to v23.2.x branch. I tried: |
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If an offset was already visible a follower must not be allowed to
truncate it as it may lead to a situation in which an offset is visible
and not readable.
Visible batches has the same replication guarantees as committed batches
as leader still waits for the majority to acknowledge message at given
offset before making it visible to the readers. This makes it possible
not to truncate offsets which were previously visible.
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Improvements