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Rounddown in FilePrefetchBuffer::Prefetch

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Summary:
FilePrefetchBuffer::Prefetch is currently rounds the offset up which does not fit its new use cases in prefetching index/filter blocks, as it would skips over some the offsets that were requested to be prefetched. This patch rounds down instead.

Fixes #3180
Closes https://github.com/facebook/rocksdb/pull/3413

Differential Revision: D6816392

Pulled By: maysamyabandeh

fbshipit-source-id: 3aaeaf59c55d72b61dacfae6d4a8e65eccb3c553
This commit is contained in:
Maysam Yabandeh 2018-01-26 12:50:48 -08:00 committed by Facebook Github Bot
parent 7fcc1d0ddf
commit 4927b4e662
2 changed files with 10 additions and 5 deletions
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2
util/aligned_buffer.h
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@ -23,6 +23,8 @@ inline size_t Roundup(size_t x, size_t y) {
return ((x + y - 1) / y) * y;
}
inline size_t Rounddown(size_t x, size_t y) { return (x / y) * y; }
// This class is to manage an aligned user
// allocated buffer for direct I/O purposes
// though can be used for any purpose.

13
util/file_reader_writer.cc
View File

@ -606,16 +606,19 @@ class ReadaheadRandomAccessFile : public RandomAccessFile {
Status FilePrefetchBuffer::Prefetch(RandomAccessFileReader* reader,
uint64_t offset, size_t n) {
size_t alignment = reader->file()->GetRequiredBufferAlignment();
uint64_t roundup_offset = Roundup(offset, alignment);
uint64_t roundup_len = Roundup(n, alignment);
uint64_t rounddown_offset = Rounddown(offset, alignment);
uint64_t roundup_end = Roundup(offset + n, alignment);
uint64_t roundup_len = roundup_end - rounddown_offset;
assert(roundup_len >= alignment);
assert(roundup_len % alignment == 0);
buffer_.Alignment(alignment);
buffer_.AllocateNewBuffer(roundup_len);
Slice result;
Status s =
reader->Read(roundup_offset, roundup_len, &result, buffer_.BufferStart());
Status s = reader->Read(rounddown_offset, roundup_len, &result,
buffer_.BufferStart());
if (s.ok()) {
buffer_offset_ = roundup_offset;
buffer_offset_ = rounddown_offset;
buffer_len_ = result.size();
}
return s;