fork of https://github.com/oxigraph/rocksdb and https://github.com/facebook/rocksdb for nextgraph and oxigraph
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410 lines
16 KiB
410 lines
16 KiB
// Copyright (c) 2014, Facebook, Inc. All rights reserved.
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// This source code is licensed under the BSD-style license found in the
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// LICENSE file in the root directory of this source tree. An additional grant
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// of patent rights can be found in the PATENTS file in the same directory.
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#ifndef ROCKSDB_LITE
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#include "table/cuckoo_table_builder.h"
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#include <assert.h>
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#include <algorithm>
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#include <limits>
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#include <string>
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#include <vector>
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#include "db/dbformat.h"
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#include "rocksdb/env.h"
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#include "rocksdb/table.h"
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#include "table/block_builder.h"
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#include "table/format.h"
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#include "table/meta_blocks.h"
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#include "util/autovector.h"
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#include "util/random.h"
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namespace rocksdb {
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const std::string CuckooTablePropertyNames::kEmptyKey =
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"rocksdb.cuckoo.bucket.empty.key";
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const std::string CuckooTablePropertyNames::kNumHashFunc =
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"rocksdb.cuckoo.hash.num";
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const std::string CuckooTablePropertyNames::kHashTableSize =
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"rocksdb.cuckoo.hash.size";
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const std::string CuckooTablePropertyNames::kValueLength =
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"rocksdb.cuckoo.value.length";
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const std::string CuckooTablePropertyNames::kIsLastLevel =
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"rocksdb.cuckoo.file.islastlevel";
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const std::string CuckooTablePropertyNames::kCuckooBlockSize =
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"rocksdb.cuckoo.hash.cuckooblocksize";
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// Obtained by running echo rocksdb.table.cuckoo | sha1sum
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extern const uint64_t kCuckooTableMagicNumber = 0x926789d0c5f17873ull;
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CuckooTableBuilder::CuckooTableBuilder(
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WritableFile* file, double hash_table_ratio,
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uint32_t max_num_hash_table, uint32_t max_search_depth,
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const Comparator* user_comparator, uint32_t cuckoo_block_size,
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uint64_t (*get_slice_hash)(const Slice&, uint32_t, uint64_t))
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: num_hash_func_(2),
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file_(file),
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hash_table_ratio_(hash_table_ratio),
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max_num_hash_func_(max_num_hash_table),
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max_search_depth_(max_search_depth),
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cuckoo_block_size_(std::max(1U, cuckoo_block_size)),
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is_last_level_file_(false),
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has_seen_first_key_(false),
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ucomp_(user_comparator),
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get_slice_hash_(get_slice_hash),
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closed_(false) {
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properties_.num_entries = 0;
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// Data is in a huge block.
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properties_.num_data_blocks = 1;
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properties_.index_size = 0;
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properties_.filter_size = 0;
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}
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void CuckooTableBuilder::Add(const Slice& key, const Slice& value) {
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if (properties_.num_entries >= kMaxVectorIdx - 1) {
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status_ = Status::NotSupported("Number of keys in a file must be < 2^32-1");
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return;
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}
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ParsedInternalKey ikey;
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if (!ParseInternalKey(key, &ikey)) {
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status_ = Status::Corruption("Unable to parse key into inernal key.");
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return;
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}
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// Determine if we can ignore the sequence number and value type from
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// internal keys by looking at sequence number from first key. We assume
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// that if first key has a zero sequence number, then all the remaining
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// keys will have zero seq. no.
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if (!has_seen_first_key_) {
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is_last_level_file_ = ikey.sequence == 0;
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has_seen_first_key_ = true;
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smallest_user_key_.assign(ikey.user_key.data(), ikey.user_key.size());
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largest_user_key_.assign(ikey.user_key.data(), ikey.user_key.size());
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}
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// Even if one sequence number is non-zero, then it is not last level.
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assert(!is_last_level_file_ || ikey.sequence == 0);
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if (is_last_level_file_) {
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kvs_.emplace_back(std::make_pair(
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ikey.user_key.ToString(), value.ToString()));
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} else {
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kvs_.emplace_back(std::make_pair(key.ToString(), value.ToString()));
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}
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properties_.num_entries++;
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// In order to fill the empty buckets in the hash table, we identify a
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// key which is not used so far (unused_user_key). We determine this by
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// maintaining smallest and largest keys inserted so far in bytewise order
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// and use them to find a key outside this range in Finish() operation.
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// Note that this strategy is independent of user comparator used here.
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if (ikey.user_key.compare(smallest_user_key_) < 0) {
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smallest_user_key_.assign(ikey.user_key.data(), ikey.user_key.size());
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} else if (ikey.user_key.compare(largest_user_key_) > 0) {
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largest_user_key_.assign(ikey.user_key.data(), ikey.user_key.size());
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}
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}
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Status CuckooTableBuilder::MakeHashTable(std::vector<CuckooBucket>* buckets) {
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uint64_t hash_table_size = kvs_.size() / hash_table_ratio_;
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buckets->resize(hash_table_size + cuckoo_block_size_ - 1);
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uint64_t make_space_for_key_call_id = 0;
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for (uint32_t vector_idx = 0; vector_idx < kvs_.size(); vector_idx++) {
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uint64_t bucket_id;
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bool bucket_found = false;
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autovector<uint64_t> hash_vals;
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Slice user_key = is_last_level_file_ ? kvs_[vector_idx].first :
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ExtractUserKey(kvs_[vector_idx].first);
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for (uint32_t hash_cnt = 0; hash_cnt < num_hash_func_ && !bucket_found;
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++hash_cnt) {
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uint64_t hash_val = get_slice_hash_(user_key, hash_cnt, hash_table_size);
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// If there is a collision, check next cuckoo_block_size_ locations for
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// empty locations. While checking, if we reach end of the hash table,
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// stop searching and proceed for next hash function.
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for (uint32_t block_idx = 0; block_idx < cuckoo_block_size_;
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++block_idx, ++hash_val) {
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if ((*buckets)[hash_val].vector_idx == kMaxVectorIdx) {
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bucket_id = hash_val;
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bucket_found = true;
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break;
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} else {
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if (ucomp_->Compare(user_key, is_last_level_file_
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? Slice(kvs_[(*buckets)[hash_val].vector_idx].first)
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: ExtractUserKey(
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kvs_[(*buckets)[hash_val].vector_idx].first)) == 0) {
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return Status::NotSupported("Same key is being inserted again.");
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}
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hash_vals.push_back(hash_val);
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}
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}
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}
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while (!bucket_found && !MakeSpaceForKey(hash_vals,
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hash_table_size, ++make_space_for_key_call_id, buckets, &bucket_id)) {
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// Rehash by increashing number of hash tables.
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if (num_hash_func_ >= max_num_hash_func_) {
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return Status::NotSupported("Too many collisions. Unable to hash.");
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}
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// We don't really need to rehash the entire table because old hashes are
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// still valid and we only increased the number of hash functions.
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uint64_t hash_val = get_slice_hash_(user_key,
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num_hash_func_, hash_table_size);
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++num_hash_func_;
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for (uint32_t block_idx = 0; block_idx < cuckoo_block_size_;
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++block_idx, ++hash_val) {
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if ((*buckets)[hash_val].vector_idx == kMaxVectorIdx) {
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bucket_found = true;
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bucket_id = hash_val;
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break;
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} else {
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hash_vals.push_back(hash_val);
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}
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}
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}
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(*buckets)[bucket_id].vector_idx = vector_idx;
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}
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return Status::OK();
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}
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Status CuckooTableBuilder::Finish() {
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assert(!closed_);
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closed_ = true;
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std::vector<CuckooBucket> buckets;
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Status s = MakeHashTable(&buckets);
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if (!s.ok()) {
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return s;
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}
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// Determine unused_user_key to fill empty buckets.
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std::string unused_bucket;
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if (!kvs_.empty()) {
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std::string unused_user_key = smallest_user_key_;
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int curr_pos = unused_user_key.size() - 1;
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while (curr_pos >= 0) {
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--unused_user_key[curr_pos];
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if (Slice(unused_user_key).compare(smallest_user_key_) < 0) {
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break;
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}
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--curr_pos;
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}
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if (curr_pos < 0) {
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// Try using the largest key to identify an unused key.
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unused_user_key = largest_user_key_;
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curr_pos = unused_user_key.size() - 1;
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while (curr_pos >= 0) {
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++unused_user_key[curr_pos];
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if (Slice(unused_user_key).compare(largest_user_key_) > 0) {
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break;
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}
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--curr_pos;
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}
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}
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if (curr_pos < 0) {
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return Status::Corruption("Unable to find unused key");
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}
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if (is_last_level_file_) {
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unused_bucket = unused_user_key;
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} else {
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ParsedInternalKey ikey(unused_user_key, 0, kTypeValue);
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AppendInternalKey(&unused_bucket, ikey);
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}
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}
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properties_.fixed_key_len = unused_bucket.size();
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uint32_t value_length = kvs_.empty() ? 0 : kvs_[0].second.size();
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uint32_t bucket_size = value_length + properties_.fixed_key_len;
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properties_.user_collected_properties[
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CuckooTablePropertyNames::kValueLength].assign(
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reinterpret_cast<const char*>(&value_length), sizeof(value_length));
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unused_bucket.resize(bucket_size, 'a');
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// Write the table.
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uint32_t num_added = 0;
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for (auto& bucket : buckets) {
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if (bucket.vector_idx == kMaxVectorIdx) {
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s = file_->Append(Slice(unused_bucket));
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} else {
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++num_added;
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s = file_->Append(kvs_[bucket.vector_idx].first);
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if (s.ok()) {
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s = file_->Append(kvs_[bucket.vector_idx].second);
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}
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}
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if (!s.ok()) {
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return s;
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}
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}
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assert(num_added == NumEntries());
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properties_.raw_key_size = num_added * properties_.fixed_key_len;
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properties_.raw_value_size = num_added * value_length;
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uint64_t offset = buckets.size() * bucket_size;
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properties_.data_size = offset;
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unused_bucket.resize(properties_.fixed_key_len);
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properties_.user_collected_properties[
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CuckooTablePropertyNames::kEmptyKey] = unused_bucket;
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properties_.user_collected_properties[
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CuckooTablePropertyNames::kNumHashFunc].assign(
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reinterpret_cast<char*>(&num_hash_func_), sizeof(num_hash_func_));
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uint64_t hash_table_size = buckets.size() - cuckoo_block_size_ + 1;
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properties_.user_collected_properties[
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CuckooTablePropertyNames::kHashTableSize].assign(
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reinterpret_cast<const char*>(&hash_table_size),
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sizeof(hash_table_size));
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properties_.user_collected_properties[
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CuckooTablePropertyNames::kIsLastLevel].assign(
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reinterpret_cast<const char*>(&is_last_level_file_),
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sizeof(is_last_level_file_));
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properties_.user_collected_properties[
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CuckooTablePropertyNames::kCuckooBlockSize].assign(
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reinterpret_cast<const char*>(&cuckoo_block_size_),
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sizeof(cuckoo_block_size_));
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// Write meta blocks.
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MetaIndexBuilder meta_index_builder;
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PropertyBlockBuilder property_block_builder;
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property_block_builder.AddTableProperty(properties_);
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property_block_builder.Add(properties_.user_collected_properties);
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Slice property_block = property_block_builder.Finish();
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BlockHandle property_block_handle;
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property_block_handle.set_offset(offset);
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property_block_handle.set_size(property_block.size());
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s = file_->Append(property_block);
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offset += property_block.size();
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if (!s.ok()) {
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return s;
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}
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meta_index_builder.Add(kPropertiesBlock, property_block_handle);
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Slice meta_index_block = meta_index_builder.Finish();
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BlockHandle meta_index_block_handle;
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meta_index_block_handle.set_offset(offset);
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meta_index_block_handle.set_size(meta_index_block.size());
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s = file_->Append(meta_index_block);
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if (!s.ok()) {
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return s;
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}
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Footer footer(kCuckooTableMagicNumber);
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footer.set_metaindex_handle(meta_index_block_handle);
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footer.set_index_handle(BlockHandle::NullBlockHandle());
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std::string footer_encoding;
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footer.EncodeTo(&footer_encoding);
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s = file_->Append(footer_encoding);
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return s;
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}
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void CuckooTableBuilder::Abandon() {
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assert(!closed_);
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closed_ = true;
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}
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uint64_t CuckooTableBuilder::NumEntries() const {
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return properties_.num_entries;
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}
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uint64_t CuckooTableBuilder::FileSize() const {
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if (closed_) {
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return file_->GetFileSize();
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} else if (properties_.num_entries == 0) {
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return 0;
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}
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// This is not the actual size of the file as we need to account for
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// hash table ratio. This returns the size of filled buckets in the table
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// scaled up by a factor of 1/hash_table_ratio.
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return ((kvs_[0].first.size() + kvs_[0].second.size()) *
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properties_.num_entries) / hash_table_ratio_;
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}
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// This method is invoked when there is no place to insert the target key.
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// It searches for a set of elements that can be moved to accommodate target
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// key. The search is a BFS graph traversal with first level (hash_vals)
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// being all the buckets target key could go to.
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// Then, from each node (curr_node), we find all the buckets that curr_node
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// could go to. They form the children of curr_node in the tree.
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// We continue the traversal until we find an empty bucket, in which case, we
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// move all elements along the path from first level to this empty bucket, to
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// make space for target key which is inserted at first level (*bucket_id).
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// If tree depth exceedes max depth, we return false indicating failure.
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bool CuckooTableBuilder::MakeSpaceForKey(
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const autovector<uint64_t>& hash_vals,
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const uint64_t hash_table_size,
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const uint64_t make_space_for_key_call_id,
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std::vector<CuckooBucket>* buckets,
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uint64_t* bucket_id) {
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struct CuckooNode {
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uint64_t bucket_id;
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uint32_t depth;
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uint32_t parent_pos;
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CuckooNode(uint64_t bucket_id, uint32_t depth, int parent_pos)
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: bucket_id(bucket_id), depth(depth), parent_pos(parent_pos) {}
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};
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// This is BFS search tree that is stored simply as a vector.
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// Each node stores the index of parent node in the vector.
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std::vector<CuckooNode> tree;
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// We want to identify already visited buckets in the current method call so
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// that we don't add same buckets again for exploration in the tree.
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// We do this by maintaining a count of current method call in
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// make_space_for_key_call_id, which acts as a unique id for this invocation
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// of the method. We store this number into the nodes that we explore in
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// current method call.
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// It is unlikely for the increment operation to overflow because the maximum
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// no. of times this will be called is <= max_num_hash_func_ + kvs_.size().
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for (uint32_t hash_cnt = 0; hash_cnt < num_hash_func_; ++hash_cnt) {
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uint64_t bucket_id = hash_vals[hash_cnt];
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(*buckets)[bucket_id].make_space_for_key_call_id =
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make_space_for_key_call_id;
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tree.push_back(CuckooNode(bucket_id, 0, 0));
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}
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bool null_found = false;
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uint32_t curr_pos = 0;
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while (!null_found && curr_pos < tree.size()) {
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CuckooNode& curr_node = tree[curr_pos];
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uint32_t curr_depth = curr_node.depth;
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if (curr_depth >= max_search_depth_) {
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break;
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}
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CuckooBucket& curr_bucket = (*buckets)[curr_node.bucket_id];
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for (uint32_t hash_cnt = 0;
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hash_cnt < num_hash_func_ && !null_found; ++hash_cnt) {
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uint64_t child_bucket_id = get_slice_hash_(
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is_last_level_file_ ? kvs_[curr_bucket.vector_idx].first
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: ExtractUserKey(Slice(kvs_[curr_bucket.vector_idx].first)),
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hash_cnt, hash_table_size);
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for (uint32_t block_idx = 0; block_idx < cuckoo_block_size_;
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++block_idx, ++child_bucket_id) {
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if ((*buckets)[child_bucket_id].make_space_for_key_call_id ==
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make_space_for_key_call_id) {
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continue;
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}
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(*buckets)[child_bucket_id].make_space_for_key_call_id =
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make_space_for_key_call_id;
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tree.push_back(CuckooNode(child_bucket_id, curr_depth + 1,
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curr_pos));
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if ((*buckets)[child_bucket_id].vector_idx == kMaxVectorIdx) {
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null_found = true;
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break;
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}
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}
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}
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++curr_pos;
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}
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if (null_found) {
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// There is an empty node in tree.back(). Now, traverse the path from this
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// empty node to top of the tree and at every node in the path, replace
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// child with the parent. Stop when first level is reached in the tree
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// (happens when 0 <= bucket_to_replace_pos < num_hash_func_) and return
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// this location in first level for target key to be inserted.
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uint32_t bucket_to_replace_pos = tree.size()-1;
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while (bucket_to_replace_pos >= num_hash_func_) {
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CuckooNode& curr_node = tree[bucket_to_replace_pos];
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(*buckets)[curr_node.bucket_id] =
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(*buckets)[tree[curr_node.parent_pos].bucket_id];
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bucket_to_replace_pos = curr_node.parent_pos;
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}
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*bucket_id = tree[bucket_to_replace_pos].bucket_id;
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}
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return null_found;
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}
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} // namespace rocksdb
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#endif // ROCKSDB_LITE
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