You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
rocksdb/table/data_block_hash_index.cc

127 lines
4.0 KiB

// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
#include <string>
#include <vector>
#include "rocksdb/slice.h"
#include "table/data_block_hash_index.h"
#include "util/coding.h"
#include "util/hash.h"
namespace rocksdb {
const uint32_t kSeed = 2018;
const uint32_t kSeed_tag = 214; /* second hash seed */
inline uint16_t HashToBucket(const Slice& s, uint16_t num_buckets) {
return static_cast<uint16_t>(
rocksdb::Hash(s.data(), s.size(), kSeed) % num_buckets);
}
void DataBlockHashIndexBuilder::Add(const Slice& key,
const uint16_t& restart_index) {
uint16_t idx = HashToBucket(key, num_buckets_);
/* push a TAG to avoid false postive */
/* the TAG is the hash function value of another seed */
uint16_t tag = static_cast<uint16_t>(
rocksdb::Hash(key.data(), key.size(), kSeed_tag));
buckets_[idx].push_back(tag);
buckets_[idx].push_back(restart_index);
estimate_ += 2 * sizeof(uint16_t);
}
void DataBlockHashIndexBuilder::Finish(std::string& buffer) {
// offset is the byte offset within the buffer
std::vector<uint16_t> bucket_offsets(num_buckets_, 0);
uint16_t map_start = static_cast<uint16_t>(buffer.size());
// write each bucket to the string
for (uint16_t i = 0; i < num_buckets_; i++) {
// remember the start offset of the buckets in bucket_offsets
bucket_offsets[i] = static_cast<uint16_t>(buffer.size());
for (uint16_t elem : buckets_[i]) {
// the elem is alternative "TAG" and "offset"
PutFixed16(&buffer, elem);
}
}
// write the bucket_offsets
for (uint16_t i = 0; i < num_buckets_; i++) {
PutFixed16(&buffer, bucket_offsets[i]);
}
// write NUM_BUCK
PutFixed16(&buffer, num_buckets_);
// write MAP_START
PutFixed16(&buffer, map_start);
// Because we use uint16_t address, we only support block less than 64KB
assert(buffer.size() < (1 << 16));
}
void DataBlockHashIndexBuilder::Reset() {
// buckets_.clear();
std::fill(buckets_.begin(), buckets_.end(), std::vector<uint16_t>());
estimate_ = 0;
}
DataBlockHashIndex::DataBlockHashIndex(Slice block_content) {
assert(block_content.size() >=
2 * sizeof(uint16_t)); // NUM_BUCK and MAP_START
data_ = block_content.data();
size_ = static_cast<uint16_t>(block_content.size());
map_start_ = data_ + DecodeFixed16(data_ + size_ - sizeof(uint16_t));
assert(map_start_ < data_ + size_);
num_buckets_ = DecodeFixed16(data_ + size_ - 2 * sizeof(uint16_t));
assert(num_buckets_ > 0);
assert(size_ >= sizeof(uint16_t) * (2 + num_buckets_));
bucket_table_ = data_ + size_ - sizeof(uint16_t) * (2 + num_buckets_);
assert(map_start_ < bucket_table_);
}
DataBlockHashIndexIterator* DataBlockHashIndex::NewIterator(
const Slice& key) const {
uint16_t idx = HashToBucket(key, num_buckets_);
uint16_t bucket_off = DecodeFixed16(bucket_table_ + idx * sizeof(uint16_t));
const char* limit;
if (idx < num_buckets_ - 1) {
// limited by the start offset of the next bucket
limit = data_ + DecodeFixed16(bucket_table_ + (idx + 1) * sizeof(uint16_t));
} else {
// limited by the location of the NUM_BUCK
limit = data_ + (size_ - 2 * sizeof(uint16_t));
}
uint16_t tag = (uint16_t)rocksdb::Hash(key.data(), key.size(), kSeed_tag);
return new DataBlockHashIndexIterator(data_ + bucket_off, limit, tag);
}
bool DataBlockHashIndexIterator::Valid() {
return current_ < end_;
}
void DataBlockHashIndexIterator::Next() {
for (current_ += 2 * sizeof(uint16_t); current_ < end_;
current_ += 2 * sizeof(uint16_t)) {
// stop at a offset that match the tag, i.e. a possible match
uint16_t tag_found = DecodeFixed16(current_);
if (tag_found == tag_) {
break;
}
}
}
uint16_t DataBlockHashIndexIterator::Value() {
return DecodeFixed16(current_ + sizeof(uint16_t));
}
} // namespace rocksdb