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@ajkr
ajkr committed Jun 10, 2020
1 parent acb69e1 commit 463f274
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Showing 3 changed files with 34 additions and 27 deletions.
3 changes: 3 additions & 0 deletions HISTORY.md
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,9 @@
* Generate file checksum in SstFileWriter if Options.file_checksum_gen_factory is set. The checksum and checksum function name are stored in ExternalSstFileInfo after the sst file write is finished.
* Add a value_size_soft_limit in read options which limits the cumulative value size of keys read in batches in MultiGet. Once the cumulative value size of found keys exceeds read_options.value_size_soft_limit, all the remaining keys are returned with status Abort without further finding their values. By default the value_size_soft_limit is std::numeric_limits<uint64_t>::max().

### Performance Improvements
* Eliminate redundant key comparisons during random access in block-based tables.

## 6.10 (5/2/2020)
### Bug Fixes
* Fix wrong result being read from ingested file. May happen when a key in the file happen to be prefix of another key also in the file. The issue can further cause more data corruption. The issue exists with rocksdb >= 5.0.0 since DB::IngestExternalFile() was introduced.
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54 changes: 29 additions & 25 deletions table/block_based/block.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -245,14 +245,14 @@ void DataBlockIter::Seek(const Slice& target) {
return;
}
uint32_t index = 0;
bool is_index_key_result = false;
bool skip_linear_scan = false;
bool ok = BinarySeek<DecodeKey>(seek_key, 0, num_restarts_ - 1, &index,
&is_index_key_result, comparator_);
&skip_linear_scan, comparator_);

if (!ok) {
return;
}
ScanAfterBinarySeek(seek_key, index, is_index_key_result, comparator_);
FindKeyAfterBinarySeek(seek_key, index, skip_linear_scan, comparator_);
}

// Optimized Seek for point lookup for an internal key `target`
Expand Down Expand Up @@ -386,7 +386,7 @@ void IndexBlockIter::Seek(const Slice& target) {
}
status_ = Status::OK();
uint32_t index = 0;
bool is_index_key_result = false;
bool skip_linear_scan = false;
bool ok = false;
if (prefix_index_) {
bool prefix_may_exist = true;
Expand All @@ -400,19 +400,19 @@ void IndexBlockIter::Seek(const Slice& target) {
}
// restart interval must be one when hash search is enabled so the binary
// search simply lands at the right place.
is_index_key_result = true;
skip_linear_scan = true;
} else if (value_delta_encoded_) {
ok = BinarySeek<DecodeKeyV4>(seek_key, 0, num_restarts_ - 1, &index,
&is_index_key_result, comparator_);
&skip_linear_scan, comparator_);
} else {
ok = BinarySeek<DecodeKey>(seek_key, 0, num_restarts_ - 1, &index,
&is_index_key_result, comparator_);
&skip_linear_scan, comparator_);
}

if (!ok) {
return;
}
ScanAfterBinarySeek(seek_key, index, is_index_key_result, comparator_);
FindKeyAfterBinarySeek(seek_key, index, skip_linear_scan, comparator_);
}

void DataBlockIter::SeekForPrev(const Slice& target) {
Expand All @@ -422,14 +422,14 @@ void DataBlockIter::SeekForPrev(const Slice& target) {
return;
}
uint32_t index = 0;
bool is_index_key_result = false;
bool skip_linear_scan = false;
bool ok = BinarySeek<DecodeKey>(seek_key, 0, num_restarts_ - 1, &index,
&is_index_key_result, comparator_);
&skip_linear_scan, comparator_);

if (!ok) {
return;
}
ScanAfterBinarySeek(seek_key, index, is_index_key_result, comparator_);
FindKeyAfterBinarySeek(seek_key, index, skip_linear_scan, comparator_);

if (!Valid()) {
SeekToLast();
Expand Down Expand Up @@ -649,13 +649,17 @@ void IndexBlockIter::DecodeCurrentValue(uint32_t shared) {
}

template <class TValue>
void BlockIter<TValue>::ScanAfterBinarySeek(const Slice& target, uint32_t index,
bool is_index_key_result,
const Comparator* comp) {
// Linear search (within restart block) for first key >= target
void BlockIter<TValue>::FindKeyAfterBinarySeek(const Slice& target,
uint32_t index,
bool skip_linear_scan,
const Comparator* comp) {
// SeekToRestartPoint() only does the lookup in the restart block. We need
// to follow it up with Next() to position the iterator at the restart key.
SeekToRestartPoint(index);
Next();
if (!is_index_key_result) {

if (!skip_linear_scan) {
// Linear search (within restart block) for first key >= target
uint32_t max_offset;
if (index + 1 < num_restarts_) {
// We are in a non-last restart interval. Since `BinarySeek()` guarantees
Expand Down Expand Up @@ -687,14 +691,14 @@ void BlockIter<TValue>::ScanAfterBinarySeek(const Slice& target, uint32_t index,
// contain duplicate keys. It is guaranteed that the restart key at `*index + 1`
// is strictly greater than `target` or does not exist (this can be used to
// elide a comparison when linear scan reaches all the way to the next restart
// key). Furthermore, `*is_index_key_result` is set to indicate whether the
// `*index`th restart key is the final result so we can elide a comparison at
// the start of the linear scan.
// key). Furthermore, `*skip_linear_scan` is set to indicate whether the
// `*index`th restart key is the final result so that key does not need to be
// compared again later.
template <class TValue>
template <typename DecodeKeyFunc>
bool BlockIter<TValue>::BinarySeek(const Slice& target, uint32_t left,
uint32_t right, uint32_t* index,
bool* is_index_key_result,
bool* skip_linear_scan,
const Comparator* comp) {
assert(left <= right);
if (restarts_ == 0) {
Expand All @@ -707,7 +711,7 @@ bool BlockIter<TValue>::BinarySeek(const Slice& target, uint32_t left,
return false;
}

*is_index_key_result = false;
*skip_linear_scan = false;
while (left < right) {
uint32_t mid = (left + right + 1) / 2;
uint32_t region_offset = GetRestartPoint(mid);
Expand All @@ -730,17 +734,17 @@ bool BlockIter<TValue>::BinarySeek(const Slice& target, uint32_t left,
// after "mid" are uninteresting.
right = mid - 1;
} else {
*is_index_key_result = true;
*skip_linear_scan = true;
left = right = mid;
}
}

assert(left == right);
*index = left;
if (*index == 0) {
// Special case as we land at zero as long as restart key at index 1 is >=
// Special case as we land at zero as long as restart key at index 1 is >
// "target". We need to compare the restart key at index 0 so we can set
// `*is_index_key_result` when the 0th restart key is >= "target".
// `*skip_linear_scan` when the 0th restart key is >= "target".
//
// GetRestartPoint() is always zero for restart key zero; skip the restart
// block access.
Expand All @@ -754,7 +758,7 @@ bool BlockIter<TValue>::BinarySeek(const Slice& target, uint32_t left,
Slice first_key(key_ptr, non_shared);
raw_key_.SetKey(first_key, false /* copy */);
int cmp = comp->Compare(applied_key_.UpdateAndGetKey(), target);
*is_index_key_result = cmp >= 0;
*skip_linear_scan = cmp >= 0;
}
return true;
}
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4 changes: 2 additions & 2 deletions table/block_based/block.h
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Original file line number Diff line number Diff line change
Expand Up @@ -411,8 +411,8 @@ class BlockIter : public InternalIteratorBase<TValue> {
uint32_t* index, bool* is_index_key_result,
const Comparator* comp);

void ScanAfterBinarySeek(const Slice& target, uint32_t index,
bool is_index_key_result, const Comparator* comp);
void FindKeyAfterBinarySeek(const Slice& target, uint32_t index,
bool is_index_key_result, const Comparator* comp);
};

class DataBlockIter final : public BlockIter<Slice> {
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