9d66d6d13e
Summary: Primarily, this change reserves space in the std::string for building the next block once a block is finished, using `block_size` as reservation size. Note: also tried reusing same std::string in the common "unbuffered" path but that showed no benefit or regression. Secondarily, this slightly reduces the work in resetting `restarts_`. Pull Request resolved: https://github.com/facebook/rocksdb/pull/9039 Test Plan: TEST_TMPDIR=/dev/shm/rocksdb1 ./db_bench -benchmarks=fillseq -memtablerep=vector -allow_concurrent_memtable_write=false -num=50000000 Compiled with DEBUG_LEVEL=0 Test vs. control runs simulaneous for better accuracy, units = ops/sec Run 1, Primary change only: 292697 vs. 280267 (+4.4%) Run 2, Primary change only: 288763 vs. 279621 (+3.3%) Run 1, Secondary change only: 260065 vs. 254232 (+2.3%) Run 2, Secondary change only: 275925 vs. 272248 (+1.4%) Run 1, Both changes: 284890 vs. 270372 (+5.3%) Run 2, Both changes: 263511 vs. 258188 (+2.0%) Reviewed By: zhichao-cao Differential Revision: D31701253 Pulled By: pdillinger fbshipit-source-id: 7e40810afbb98e6b6446955e77bda59e69b19ffd
201 lines
7.2 KiB
C++
201 lines
7.2 KiB
C++
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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//
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// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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//
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// BlockBuilder generates blocks where keys are prefix-compressed:
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//
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// When we store a key, we drop the prefix shared with the previous
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// string. This helps reduce the space requirement significantly.
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// Furthermore, once every K keys, we do not apply the prefix
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// compression and store the entire key. We call this a "restart
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// point". The tail end of the block stores the offsets of all of the
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// restart points, and can be used to do a binary search when looking
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// for a particular key. Values are stored as-is (without compression)
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// immediately following the corresponding key.
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//
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// An entry for a particular key-value pair has the form:
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// shared_bytes: varint32
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// unshared_bytes: varint32
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// value_length: varint32
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// key_delta: char[unshared_bytes]
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// value: char[value_length]
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// shared_bytes == 0 for restart points.
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//
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// The trailer of the block has the form:
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// restarts: uint32[num_restarts]
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// num_restarts: uint32
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// restarts[i] contains the offset within the block of the ith restart point.
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#include "table/block_based/block_builder.h"
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#include <assert.h>
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#include <algorithm>
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#include "db/dbformat.h"
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#include "rocksdb/comparator.h"
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#include "table/block_based/data_block_footer.h"
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#include "util/coding.h"
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namespace ROCKSDB_NAMESPACE {
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BlockBuilder::BlockBuilder(
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int block_restart_interval, bool use_delta_encoding,
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bool use_value_delta_encoding,
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BlockBasedTableOptions::DataBlockIndexType index_type,
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double data_block_hash_table_util_ratio)
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: block_restart_interval_(block_restart_interval),
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use_delta_encoding_(use_delta_encoding),
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use_value_delta_encoding_(use_value_delta_encoding),
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restarts_(1, 0), // First restart point is at offset 0
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counter_(0),
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finished_(false) {
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switch (index_type) {
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case BlockBasedTableOptions::kDataBlockBinarySearch:
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break;
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case BlockBasedTableOptions::kDataBlockBinaryAndHash:
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data_block_hash_index_builder_.Initialize(
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data_block_hash_table_util_ratio);
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break;
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default:
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assert(0);
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}
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assert(block_restart_interval_ >= 1);
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estimate_ = sizeof(uint32_t) + sizeof(uint32_t);
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}
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void BlockBuilder::Reset() {
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buffer_.clear();
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restarts_.resize(1); // First restart point is at offset 0
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assert(restarts_[0] == 0);
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estimate_ = sizeof(uint32_t) + sizeof(uint32_t);
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counter_ = 0;
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finished_ = false;
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last_key_.clear();
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if (data_block_hash_index_builder_.Valid()) {
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data_block_hash_index_builder_.Reset();
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}
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}
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void BlockBuilder::SwapAndReset(std::string& buffer) {
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std::swap(buffer_, buffer);
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Reset();
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}
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size_t BlockBuilder::EstimateSizeAfterKV(const Slice& key,
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const Slice& value) const {
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size_t estimate = CurrentSizeEstimate();
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// Note: this is an imprecise estimate as it accounts for the whole key size
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// instead of non-shared key size.
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estimate += key.size();
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// In value delta encoding we estimate the value delta size as half the full
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// value size since only the size field of block handle is encoded.
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estimate +=
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!use_value_delta_encoding_ || (counter_ >= block_restart_interval_)
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? value.size()
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: value.size() / 2;
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if (counter_ >= block_restart_interval_) {
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estimate += sizeof(uint32_t); // a new restart entry.
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}
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estimate += sizeof(int32_t); // varint for shared prefix length.
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// Note: this is an imprecise estimate as we will have to encoded size, one
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// for shared key and one for non-shared key.
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estimate += VarintLength(key.size()); // varint for key length.
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if (!use_value_delta_encoding_ || (counter_ >= block_restart_interval_)) {
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estimate += VarintLength(value.size()); // varint for value length.
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}
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return estimate;
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}
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Slice BlockBuilder::Finish() {
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// Append restart array
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for (size_t i = 0; i < restarts_.size(); i++) {
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PutFixed32(&buffer_, restarts_[i]);
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}
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uint32_t num_restarts = static_cast<uint32_t>(restarts_.size());
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BlockBasedTableOptions::DataBlockIndexType index_type =
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BlockBasedTableOptions::kDataBlockBinarySearch;
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if (data_block_hash_index_builder_.Valid() &&
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CurrentSizeEstimate() <= kMaxBlockSizeSupportedByHashIndex) {
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data_block_hash_index_builder_.Finish(buffer_);
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index_type = BlockBasedTableOptions::kDataBlockBinaryAndHash;
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}
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// footer is a packed format of data_block_index_type and num_restarts
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uint32_t block_footer = PackIndexTypeAndNumRestarts(index_type, num_restarts);
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PutFixed32(&buffer_, block_footer);
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finished_ = true;
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return Slice(buffer_);
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}
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void BlockBuilder::Add(const Slice& key, const Slice& value,
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const Slice* const delta_value) {
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assert(!finished_);
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assert(counter_ <= block_restart_interval_);
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assert(!use_value_delta_encoding_ || delta_value);
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size_t shared = 0; // number of bytes shared with prev key
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if (counter_ >= block_restart_interval_) {
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// Restart compression
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restarts_.push_back(static_cast<uint32_t>(buffer_.size()));
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estimate_ += sizeof(uint32_t);
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counter_ = 0;
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if (use_delta_encoding_) {
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// Update state
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last_key_.assign(key.data(), key.size());
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}
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} else if (use_delta_encoding_) {
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Slice last_key_piece(last_key_);
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// See how much sharing to do with previous string
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shared = key.difference_offset(last_key_piece);
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// Update state
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// We used to just copy the changed data here, but it appears to be
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// faster to just copy the whole thing.
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last_key_.assign(key.data(), key.size());
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}
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const size_t non_shared = key.size() - shared;
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const size_t curr_size = buffer_.size();
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if (use_value_delta_encoding_) {
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// Add "<shared><non_shared>" to buffer_
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PutVarint32Varint32(&buffer_, static_cast<uint32_t>(shared),
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static_cast<uint32_t>(non_shared));
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} else {
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// Add "<shared><non_shared><value_size>" to buffer_
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PutVarint32Varint32Varint32(&buffer_, static_cast<uint32_t>(shared),
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static_cast<uint32_t>(non_shared),
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static_cast<uint32_t>(value.size()));
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}
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// Add string delta to buffer_ followed by value
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buffer_.append(key.data() + shared, non_shared);
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// Use value delta encoding only when the key has shared bytes. This would
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// simplify the decoding, where it can figure which decoding to use simply by
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// looking at the shared bytes size.
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if (shared != 0 && use_value_delta_encoding_) {
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buffer_.append(delta_value->data(), delta_value->size());
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} else {
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buffer_.append(value.data(), value.size());
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}
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if (data_block_hash_index_builder_.Valid()) {
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data_block_hash_index_builder_.Add(ExtractUserKey(key),
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restarts_.size() - 1);
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}
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counter_++;
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estimate_ += buffer_.size() - curr_size;
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}
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} // namespace ROCKSDB_NAMESPACE
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