Prefetch buffer may not contain all of requested data if EOF is hit #13376
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
archang19
commented
Feb 6, 2025
file/file_prefetch_buffer.cc
Outdated
| @@ -865,8 +865,7 @@ bool FilePrefetchBuffer::TryReadFromCacheUntracked( | |||
| if (copy_to_overlap_buffer) { | |||
| buf = overlap_buf_; | |||
| } | |||
| assert(buf->offset_ <= offset); | |||
| assert(buf->IsDataBlockInBuffer(offset, n)); | |||
| assert(buf->IsOffsetInBuffer(offset)); | |||
| uint64_t offset_in_buffer = offset - buf->offset_; | |||
| *result = Slice(buf->buffer_.BufferStart() + offset_in_buffer, n); | |||
There was a problem hiding this comment.
I think this is a bug from this 2019 commit siying@3737d06: https://github.com/siying/rocksdb/blob/4eb51130917c260f5637731cd77baaa45dfdc5ec/file/file_prefetch_buffer.cc#L130
What happens if we try to read more bytes than there exists in the file? I don't think we always want to return n bytes.
archang19
force-pushed
the
prefetch-update-assertion
branch
2 times, most recently
from
5507d62 to
0e22c2e
Compare
archang19
force-pushed
the
prefetch-update-assertion
branch
from
0e22c2e to
159dd79
Compare
|
@archang19 has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator. |
|
fyi @jowlyzhang this error affected the warm storage crash tests |
anand1976
approved these changes
Feb 7, 2025
|
@archang19 merged this pull request in c1fb33e. |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Summary
There was a stress test that failed at the assertion check for
IsDataBlockInBuffer.IsDataBlockInBufferis too strict of a condition if we are trying to read past the end of the file.This seems to be a bug from the original 2019 commit siying@3737d06: https://github.com/siying/rocksdb/blob/4eb51130917c260f5637731cd77baaa45dfdc5ec/file/file_prefetch_buffer.cc#L130
If the caller tries requesting more bytes than are available, then we still return
nbytes, even if the buffer really only containsm < nbytes.Test Plan
I added a unit test which caused the original
IsDataBlockInBufferassertion to fail. I also updated the unit test to check for the result size, which triggered the bug (without this fix) where we return a size ofneven if less thannbytes exist.