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set readahead buffer size from roundup(user_size) + 4k to roundup(use… 

Summary:
Users usually set readahead buffer to a multiple of 4k, more than that, usually a multiple of blocks.
So previously we set real buffer size 512 * n + 4k, which may introduce an additional block reading.
Closes https://github.com/facebook/rocksdb/pull/2138

Differential Revision: D4871504

Pulled By: lightmark

fbshipit-source-id: b070faa51d92e976e8e8468c00692699e585e243
This commit is contained in:
Aaron Gao 2017-04-11 16:59:50 -07:00 committed by Facebook Github Bot
parent ba7da434ae
commit 10d7546961
1 changed files with 5 additions and 5 deletions
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10
util/file_reader_writer.cc
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@ -441,7 +441,7 @@ class ReadaheadRandomAccessFile : public RandomAccessFile {
buffer_len_(0) {
if (!forward_calls_) {
buffer_.Alignment(alignment_);
buffer_.AllocateNewBuffer(readahead_size_ + alignment_);
buffer_.AllocateNewBuffer(readahead_size_);
} else if (readahead_size_ > 0) {
file_->EnableReadAhead();
}
@ -453,7 +453,7 @@ class ReadaheadRandomAccessFile : public RandomAccessFile {
virtual Status Read(uint64_t offset, size_t n, Slice* result,
char* scratch) const override {
if (n >= readahead_size_) {
if (n + alignment_ >= readahead_size_) {
return file_->Read(offset, n, result, scratch);
}
@ -475,7 +475,7 @@ class ReadaheadRandomAccessFile : public RandomAccessFile {
if (TryReadFromCache_(offset, n, &cached_len, scratch) &&
(cached_len == n ||
// End of file
buffer_len_ < readahead_size_ + alignment_)) {
buffer_len_ < readahead_size_)) {
*result = Slice(scratch, cached_len);
return Status::OK();
}
@ -484,8 +484,8 @@ class ReadaheadRandomAccessFile : public RandomAccessFile {
// chunk_offset equals to advanced_offset
size_t chunk_offset = TruncateToPageBoundary(alignment_, advanced_offset);
Slice readahead_result;
Status s = file_->Read(chunk_offset, readahead_size_ + alignment_,
&readahead_result, buffer_.BufferStart());
Status s = file_->Read(chunk_offset, readahead_size_, &readahead_result,
buffer_.BufferStart());
if (!s.ok()) {
return s;
}