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rocksdb/table/cuckoo_table_builder.cc

333 lines
11 KiB

// Copyright (c) 2013, 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 <string>
#include <vector>
#include "db/dbformat.h"
#include "rocksdb/env.h"
#include "rocksdb/table.h"
#include "table/block_builder.h"
#include "table/format.h"
#include "table/meta_blocks.h"
#include "util/autovector.h"
#include "util/random.h"
namespace rocksdb {
const std::string CuckooTablePropertyNames::kEmptyBucket =
"rocksdb.cuckoo.bucket.empty.bucket";
const std::string CuckooTablePropertyNames::kNumHashTable =
"rocksdb.cuckoo.hash.num";
const std::string CuckooTablePropertyNames::kMaxNumBuckets =
"rocksdb.cuckoo.bucket.maxnum";
// Obtained by running echo rocksdb.table.cuckoo | sha1sum
extern const uint64_t kCuckooTableMagicNumber = 0x926789d0c5f17873ull;
CuckooTableBuilder::CuckooTableBuilder(
WritableFile* file, unsigned int fixed_key_length,
unsigned int fixed_value_length, double hash_table_ratio,
unsigned int file_size, unsigned int max_num_hash_table,
unsigned int max_search_depth,
unsigned int (*GetSliceHashPtr)(const Slice&, unsigned int,
unsigned int))
: num_hash_table_(std::min((unsigned int) 4, max_num_hash_table)),
file_(file),
value_length_(fixed_value_length),
bucket_size_(fixed_key_length + fixed_value_length),
hash_table_ratio_(hash_table_ratio),
max_num_buckets_(file_size / bucket_size_),
max_num_hash_table_(max_num_hash_table),
max_search_depth_(max_search_depth),
buckets_(max_num_buckets_),
GetSliceHash(GetSliceHashPtr) {
// The bucket_size is currently not optimized for last level.
// In last level, the bucket will not contain full key.
// TODO(rbs): Find how we can determine if last level or not
// before we start adding entries into the table.
properties_.num_entries = 0;
// Data is in a huge block.
properties_.num_data_blocks = 1;
properties_.index_size = 0;
properties_.filter_size = 0;
}
CuckooTableBuilder::~CuckooTableBuilder() {
}
void CuckooTableBuilder::Add(const Slice& key, const Slice& value) {
if (NumEntries() == max_num_buckets_) {
status_ = Status::Corruption("Hash Table is full.");
return;
}
unsigned int bucket_id;
bool bucket_found = false;
autovector<unsigned int> hash_vals;
ParsedInternalKey ikey;
if (!ParseInternalKey(key, &ikey)) {
status_ = Status::Corruption("Unable to parse key into inernal key.");
return;
}
Slice user_key = ikey.user_key;
for (unsigned int hash_cnt = 0; hash_cnt < num_hash_table_; ++hash_cnt) {
unsigned int hash_val = GetSliceHash(user_key, hash_cnt, max_num_buckets_);
if (buckets_[hash_val].is_empty) {
bucket_id = hash_val;
bucket_found = true;
break;
} else {
if (user_key.compare(ExtractUserKey(buckets_[hash_val].key)) == 0) {
status_ = Status::Corruption("Same key is being inserted again.");
return;
}
hash_vals.push_back(hash_val);
}
}
while (!bucket_found && !MakeSpaceForKey(key, &bucket_id, hash_vals)) {
// Rehash by increashing number of hash tables.
if (num_hash_table_ >= max_num_hash_table_) {
status_ = Status::Corruption("Too many collissions. Unable to hash.");
return;
}
// 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.
unsigned int old_num_hash = num_hash_table_;
num_hash_table_ = std::min(num_hash_table_ + 1, max_num_hash_table_);
for (unsigned int i = old_num_hash; i < num_hash_table_; i++) {
unsigned int hash_val = GetSliceHash(user_key, i, max_num_buckets_);
if (buckets_[hash_val].is_empty) {
bucket_found = true;
bucket_id = hash_val;
break;
} else {
hash_vals.push_back(hash_val);
}
}
}
buckets_[bucket_id].key = key;
buckets_[bucket_id].value = value;
buckets_[bucket_id].is_empty = false;
if (ikey.sequence != 0) {
// This is not a last level file.
is_last_level_file_ = false;
}
properties_.num_entries++;
// We assume that the keys are inserted in sorted order. To identify an
// unused key, which will be used in filling empty buckets in the table,
// we try to find gaps between successive keys inserted. This is done by
// maintaining the previous key and comparing it with next key.
if (unused_user_key_.empty()) {
if (prev_key_.empty()) {
prev_key_ = user_key.ToString();
return;
}
std::string new_user_key = prev_key_;
new_user_key.back()++;
// We ignore carry-overs and check that it is larger than previous key.
if ((new_user_key > prev_key_) &&
(new_user_key < user_key.ToString())) {
unused_user_key_ = new_user_key;
} else {
prev_key_ = user_key.ToString();
}
}
}
Status CuckooTableBuilder::status() const { return status_; }
Status CuckooTableBuilder::Finish() {
assert(!closed_);
closed_ = true;
if (unused_user_key_.empty()) {
if (prev_key_.empty()) {
return Status::Corruption("Unable to find unused key");
}
std::string new_user_key = prev_key_;
new_user_key.back()++;
// We ignore carry-overs and check that it is larger than previous key.
if (new_user_key > prev_key_) {
unused_user_key_ = new_user_key;
} else {
return Status::Corruption("Unable to find unused key");
}
}
std::string unused_bucket;
if (is_last_level_file_) {
unused_bucket = unused_user_key_;
} else {
ParsedInternalKey ikey(unused_user_key_, 0, kTypeValue);
AppendInternalKey(&unused_bucket, ikey);
}
properties_.fixed_key_len = unused_bucket.size();
unsigned int bucket_size = unused_bucket.size() + value_length_;
// Resize to bucket size.
unused_bucket.resize(bucket_size, 'a');
// Write the table.
for (auto& bucket : buckets_) {
Status s;
if (bucket.is_empty) {
s = file_->Append(Slice(unused_bucket));
} else {
if (is_last_level_file_) {
Slice user_key = ExtractUserKey(bucket.key);
s = file_->Append(user_key);
if (s.ok()) {
s = file_->Append(bucket.value);
}
} else {
s = file_->Append(bucket.key);
if (s.ok()) {
s = file_->Append(bucket.value);
}
}
}
if (!s.ok()) {
return s;
}
}
unsigned int offset = buckets_.size() * bucket_size;
properties_.user_collected_properties[
CuckooTablePropertyNames::kEmptyBucket] = unused_bucket;
properties_.user_collected_properties[
CuckooTablePropertyNames::kNumHashTable] = std::to_string(num_hash_table_);
PutVarint32(&properties_.user_collected_properties[
CuckooTablePropertyNames::kMaxNumBuckets], max_num_buckets_);
// Write meta blocks.
MetaIndexBuilder meta_index_builer;
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());
Status s = file_->Append(property_block);
offset += property_block.size();
if (!s.ok()) {
return s;
}
meta_index_builer.Add(kPropertiesBlock, property_block_handle);
Slice meta_index_block = meta_index_builer.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 properties_.num_entries;
}
uint64_t CuckooTableBuilder::FileSize() const {
if (closed_) {
return file_->GetFileSize();
} else {
// This is not the actual size of the file as we need to account for
// hash table ratio. This returns the size of filled buckets in the table
// scaled up by a factor of 1/hash table ratio.
return (properties_.num_entries * bucket_size_) / hash_table_ratio_;
}
}
bool CuckooTableBuilder::MakeSpaceForKey(const Slice& key,
unsigned int *bucket_id, autovector<unsigned int> hash_vals) {
struct CuckooNode {
unsigned int bucket_id;
unsigned int depth;
int parent_pos;
CuckooNode(unsigned int bucket_id, unsigned int 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;
// This is a very bad way to keep track of visited nodes.
// TODO(rbs): Change this by adding a 'GetKeyPathId' field to the bucket
// and use it to track visited nodes.
std::vector<bool> buckets_visited(max_num_buckets_, false);
for (unsigned int hash_cnt = 0; hash_cnt < num_hash_table_; ++hash_cnt) {
unsigned int bucket_id = hash_vals[hash_cnt];
buckets_visited[bucket_id] = true;
tree.push_back(CuckooNode(bucket_id, 0, -1));
}
bool null_found = false;
unsigned int curr_pos = 0;
while (!null_found && curr_pos < tree.size()) {
CuckooNode& curr_node = tree[curr_pos];
if (curr_node.depth >= max_search_depth_) {
break;
}
CuckooBucket& curr_bucket = buckets_[curr_node.bucket_id];
for (unsigned int hash_cnt = 0; hash_cnt < num_hash_table_; ++hash_cnt) {
unsigned int child_bucket_id = GetSliceHash(
ExtractUserKey(curr_bucket.key), hash_cnt, max_num_buckets_);
if (child_bucket_id == curr_node.bucket_id) {
continue;
}
if (buckets_visited[child_bucket_id]) {
continue;
}
buckets_visited[child_bucket_id] = true;
tree.push_back(CuckooNode(child_bucket_id, curr_node.depth + 1,
curr_pos));
if (buckets_[child_bucket_id].is_empty) {
null_found = true;
break;
}
}
++curr_pos;
}
if (null_found) {
int bucket_to_replace_pos = tree.size()-1;
while (bucket_to_replace_pos >= 0) {
CuckooNode& curr_node = tree[bucket_to_replace_pos];
if (curr_node.parent_pos != -1) {
buckets_[curr_node.bucket_id] = buckets_[curr_node.parent_pos];
bucket_to_replace_pos = curr_node.parent_pos;
} else {
*bucket_id = curr_node.bucket_id;
return true;
}
}
return true;
} else {
return false;
}
}
} // namespace rocksdb
#endif // ROCKSDB_LITE