commitlog: Truncate segment before resuming#5116
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Don't know if it's a github bug or what but It is looking like a empty commit. |
`read_exact` doesn't distinguish between EOF and not enough bytes to fill the given buffer. We may thus consider a segment valid to be resumed, but leave in trailing bytes (less than the commit header length). That can cause silent data loss, because appending more data will render the segment corrupt: a restart will then start a new segment, leaving anything after the trailing bytes unreachable. To fix this, truncate the segment to the size determined by `Metadata::extract` before resuming writes.
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| // trailing bytes in the segment, but less than the commit header | ||
| // length. This is difficult to detect due to the use of `read_exact`, | ||
| // so ensure we remove any trailing bytes. | ||
| writer.ftruncate(tx_range.end, size_in_bytes)?; |
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I would have preferred to treat this case similar to corrupted commits i.e to return ResumedSegment::Corrupted here and let caller create new segment. . Which looks more consistent and safer behavior.
Maybe, we can check in Metadata::with_header , if reader is at EOF. wdyt?
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We'd need to look at all ways in which read_exact is used. Not sure if that gains us that much.
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read_exactdoesn't distinguish between EOF and not enough bytes to fill the given buffer. We may thus consider a segment valid to be resumed, but leave in trailing bytes (less than the commit header length). That can cause silent data loss, because appending more data will render the segment corrupt: a restart will then start a new segment, leaving anything after the trailing bytes unreachable.To fix this, truncate the segment to the size determined by
Metadata::extractbefore resuming writes.Expected complexity level and risk
2
Testing
Added a test