tomFlowee
c63519fa47
The leveldb and univalue 3rd party libraries are not installed and not needed by anyone outside of the Hub. So move them there, making it easier for 3rd party usage.
110 lines
3.6 KiB
C++
110 lines
3.6 KiB
C++
// 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_builder.h"
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#include <algorithm>
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#include <assert.h>
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#include "leveldb/comparator.h"
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#include "leveldb/table_builder.h"
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#include "util/coding.h"
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namespace leveldb {
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BlockBuilder::BlockBuilder(const Options* options)
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: options_(options),
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restarts_(),
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counter_(0),
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finished_(false) {
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assert(options->block_restart_interval >= 1);
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restarts_.push_back(0); // First restart point is at offset 0
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}
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void BlockBuilder::Reset() {
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buffer_.clear();
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restarts_.clear();
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restarts_.push_back(0); // First restart point is at offset 0
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counter_ = 0;
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finished_ = false;
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last_key_.clear();
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}
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size_t BlockBuilder::CurrentSizeEstimate() const {
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return (buffer_.size() + // Raw data buffer
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restarts_.size() * sizeof(uint32_t) + // Restart array
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sizeof(uint32_t)); // Restart array length
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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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PutFixed32(&buffer_, restarts_.size());
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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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Slice last_key_piece(last_key_);
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assert(!finished_);
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assert(counter_ <= options_->block_restart_interval);
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assert(buffer_.empty() // No values yet?
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|| options_->comparator->Compare(key, last_key_piece) > 0);
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size_t shared = 0;
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if (counter_ < options_->block_restart_interval) {
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// See how much sharing to do with previous string
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const size_t min_length = std::min(last_key_piece.size(), key.size());
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while ((shared < min_length) && (last_key_piece[shared] == key[shared])) {
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shared++;
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}
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} else {
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// Restart compression
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restarts_.push_back(buffer_.size());
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counter_ = 0;
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}
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const size_t non_shared = key.size() - shared;
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// Add "<shared><non_shared><value_size>" to buffer_
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PutVarint32(&buffer_, shared);
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PutVarint32(&buffer_, non_shared);
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PutVarint32(&buffer_, value.size());
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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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buffer_.append(value.data(), value.size());
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// Update state
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last_key_.resize(shared);
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last_key_.append(key.data() + shared, non_shared);
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assert(Slice(last_key_) == key);
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counter_++;
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}
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} // namespace leveldb
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