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Unify compaction prefetching logic #13187

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Unify compaction prefetching logic #13187

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914e424
Add precondition assertions for file prefetch buffer reads
archang19 Dec 5, 2024
4f8005f
Add error logging
archang19 Dec 6, 2024
2e81def
Probably only need this for now
archang19 Dec 6, 2024
7bed6ad
Demonstrate failing test with for_compaction=true
archang19 Dec 9, 2024
28c1ad1
Try using PrefetchInternal instead of regular Prefetch
archang19 Dec 9, 2024
eb6cc76
Update tests and implementation
archang19 Dec 9, 2024
cede5c5
Temporarily add randomized tests
archang19 Dec 10, 2024
2645f84
Fix randomized test
archang19 Dec 12, 2024
cc7fafd
Check status inside test
archang19 Dec 12, 2024
da9744a
Handle platforms with no async io support
archang19 Dec 12, 2024
d5e9134
Add test for compaction read without optimization
archang19 Dec 12, 2024
f5d481b
Make randomized test more tricky
archang19 Dec 12, 2024
f3e438f
Unify compaction read logic
archang19 Dec 27, 2024
356b3a0
Address nit comments
archang19 Dec 27, 2024
f91868a
Add another assertion
archang19 Dec 27, 2024
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40 changes: 21 additions & 19 deletions file/file_prefetch_buffer.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -771,6 +771,12 @@ bool FilePrefetchBuffer::TryReadFromCache(const IOOptions& opts,
bool FilePrefetchBuffer::TryReadFromCacheUntracked(
const IOOptions& opts, RandomAccessFileReader* reader, uint64_t offset,
size_t n, Slice* result, Status* status, bool for_compaction) {
// We disallow async IO for compaction reads since they are performed in
// the background anyways and are less latency sensitive compareed to
// user-initiated reads
(void)for_compaction;
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With the change to unify the logic, for_compaction is not used outside of this assert so we need this (void) for_compaction to prevent the compiler from complaining

assert(!for_compaction || num_buffers_ == 1);

if (track_min_offset_ && offset < min_offset_read_) {
min_offset_read_ = static_cast<size_t>(offset);
}
Expand Down Expand Up @@ -819,27 +825,22 @@ bool FilePrefetchBuffer::TryReadFromCacheUntracked(
assert(reader != nullptr);
assert(max_readahead_size_ >= readahead_size_);

if (for_compaction) {
s = Prefetch(opts, reader, offset, std::max(n, readahead_size_));
} else {
if (implicit_auto_readahead_) {
if (!IsEligibleForPrefetch(offset, n)) {
// Ignore status as Prefetch is not called.
s.PermitUncheckedError();
return false;
}
if (implicit_auto_readahead_) {
if (!IsEligibleForPrefetch(offset, n)) {
// Ignore status as Prefetch is not called.
s.PermitUncheckedError();
return false;
}

// Prefetch n + readahead_size_/2 synchronously as remaining
// readahead_size_/2 will be prefetched asynchronously if num_buffers_
// > 1.
s = PrefetchInternal(
opts, reader, offset, n,
(num_buffers_ > 1 ? readahead_size_ / 2 : readahead_size_),
copy_to_overlap_buffer);
explicit_prefetch_submitted_ = false;
}

// Prefetch n + readahead_size_/2 synchronously as remaining
// readahead_size_/2 will be prefetched asynchronously if num_buffers_
// > 1.
s = PrefetchInternal(
opts, reader, offset, n,
(num_buffers_ > 1 ? readahead_size_ / 2 : readahead_size_),
copy_to_overlap_buffer);
explicit_prefetch_submitted_ = false;
if (!s.ok()) {
if (status) {
*status = s;
Expand All @@ -853,7 +854,7 @@ bool FilePrefetchBuffer::TryReadFromCacheUntracked(
} else {
return false;
}
} else if (!for_compaction) {
} else {
UpdateStats(/*found_in_buffer=*/true, n);
}

Expand All @@ -864,6 +865,7 @@ bool FilePrefetchBuffer::TryReadFromCacheUntracked(
buf = overlap_buf_;
}
assert(buf->offset_ <= offset);
assert(buf->IsDataBlockInBuffer(offset, n));
uint64_t offset_in_buffer = offset - buf->offset_;
*result = Slice(buf->buffer_.BufferStart() + offset_in_buffer, n);
if (prefetched) {
Expand Down
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