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rocksdb/table/cuckoo_table_builder.cc

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17 KiB

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