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109 行
3.5 KiB
109 行
3.5 KiB
// 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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#include "db/memtable.h"
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#include "db/dbformat.h"
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#include "include/comparator.h"
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#include "include/env.h"
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#include "include/iterator.h"
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#include "util/coding.h"
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namespace leveldb {
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static Slice GetLengthPrefixedSlice(const char* data) {
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uint32_t len;
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const char* p = data;
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p = GetVarint32Ptr(p, p + 5, &len); // +5: we assume "p" is not corrupted
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return Slice(p, len);
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}
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MemTable::MemTable(const InternalKeyComparator& cmp)
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: comparator_(cmp),
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table_(comparator_, &arena_) {
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}
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MemTable::~MemTable() {
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}
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size_t MemTable::ApproximateMemoryUsage() { return arena_.MemoryUsage(); }
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int MemTable::KeyComparator::operator()(const char* aptr, const char* bptr)
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const {
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// Internal keys are encoded as length-prefixed strings.
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Slice a = GetLengthPrefixedSlice(aptr);
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Slice b = GetLengthPrefixedSlice(bptr);
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return comparator.Compare(a, b);
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}
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// Encode a suitable internal key target for "target" and return it.
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// Uses *scratch as scratch space, and the returned pointer will point
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// into this scratch space.
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static const char* EncodeKey(std::string* scratch, const Slice& target) {
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scratch->clear();
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PutVarint32(scratch, target.size());
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scratch->append(target.data(), target.size());
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return scratch->data();
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}
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class MemTableIterator: public Iterator {
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public:
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explicit MemTableIterator(MemTable::Table* table) {
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iter_ = new MemTable::Table::Iterator(table);
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}
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virtual ~MemTableIterator() { delete iter_; }
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virtual bool Valid() const { return iter_->Valid(); }
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virtual void Seek(const Slice& k) { iter_->Seek(EncodeKey(&tmp_, k)); }
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virtual void SeekToFirst() { iter_->SeekToFirst(); }
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virtual void SeekToLast() { iter_->SeekToLast(); }
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virtual void Next() { iter_->Next(); }
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virtual void Prev() { iter_->Prev(); }
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virtual Slice key() const { return GetLengthPrefixedSlice(iter_->key()); }
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virtual Slice value() const {
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Slice key_slice = GetLengthPrefixedSlice(iter_->key());
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return GetLengthPrefixedSlice(key_slice.data() + key_slice.size());
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}
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virtual Status status() const { return Status::OK(); }
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private:
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MemTable::Table::Iterator* iter_;
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std::string tmp_; // For passing to EncodeKey
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// No copying allowed
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MemTableIterator(const MemTableIterator&);
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void operator=(const MemTableIterator&);
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};
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Iterator* MemTable::NewIterator() {
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return new MemTableIterator(&table_);
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}
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void MemTable::Add(SequenceNumber s, ValueType type,
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const Slice& key,
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const Slice& value) {
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// Format of an entry is concatenation of:
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// key_size : varint32 of internal_key.size()
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// key bytes : char[internal_key.size()]
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// value_size : varint32 of value.size()
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// value bytes : char[value.size()]
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size_t key_size = key.size();
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size_t val_size = value.size();
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size_t internal_key_size = key_size + 8;
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const size_t encoded_len =
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VarintLength(internal_key_size) + internal_key_size +
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VarintLength(val_size) + val_size;
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char* buf = arena_.Allocate(encoded_len);
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char* p = EncodeVarint32(buf, internal_key_size);
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memcpy(p, key.data(), key_size);
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p += key_size;
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EncodeFixed64(p, (s << 8) | type);
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p += 8;
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p = EncodeVarint32(p, val_size);
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memcpy(p, value.data(), val_size);
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assert((p + val_size) - buf == encoded_len);
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table_.Insert(buf);
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}
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}
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