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146 řádky
5.1 KiB
146 řádky
5.1 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 "leveldb/comparator.h"
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#include "leveldb/env.h"
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#include "leveldb/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& comparator)
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: comparator_(comparator), refs_(0), table_(comparator_, &arena_) {}
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MemTable::~MemTable() { assert(refs_ == 0); }
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size_t MemTable::ApproximateMemoryUsage() { return arena_.MemoryUsage(); }
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int MemTable::KeyComparator::operator()(const char* aptr,
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const char* bptr) 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) : iter_(table) {}
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MemTableIterator(const MemTableIterator&) = delete;
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MemTableIterator& operator=(const MemTableIterator&) = delete;
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~MemTableIterator() override = default;
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bool Valid() const override { return iter_.Valid(); }
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void Seek(const Slice& k) override { iter_.Seek(EncodeKey(&tmp_, k)); }
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void SeekToFirst() override { iter_.SeekToFirst(); }
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void SeekToLast() override { iter_.SeekToLast(); }
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void Next() override { iter_.Next(); }
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void Prev() override { iter_.Prev(); }
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Slice key() const override { return GetLengthPrefixedSlice(iter_.key()); }
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Slice value() const override {
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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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Status status() const override { 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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};
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Iterator* MemTable::NewIterator() { return new MemTableIterator(&table_); }
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void MemTable::Add(SequenceNumber s, ValueType type, 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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// tag : uint64((sequence << 8) | type)
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// value_size : varint32 of value.size()
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// value bytes : char[value.size()],[real_value,timestamp(uint64)]
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//
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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 = VarintLength(internal_key_size) +
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internal_key_size + VarintLength(val_size) +
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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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std::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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std::memcpy(p, value.data(), val_size);//value包含timestamp,timestamp，8字节
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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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* @descrption: ttl问题场景：一个key，多个版本，其ttl的相对大小于版本号的相对大小不同
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* @param key
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* @param value
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* @param s
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* @return
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*/
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bool MemTable::Get(const LookupKey& key, std::string* value, Status* s) {
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Slice memkey = key.memtable_key();
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Table::Iterator iter(&table_);
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iter.Seek(memkey.data());
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if (iter.Valid()) {
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// entry format is:
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// klength varint32
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// userkey char[klength]
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// tag uint64
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// vlength varint32
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// value char[vlength]
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// Check that it belongs to same user key. We do not check the
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// sequence number since the Seek() call above should have skipped
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// all entries with overly large sequence numbers.
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const char* entry = iter.key();
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uint32_t key_length;
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const char* key_ptr = GetVarint32Ptr(entry, entry + 5, &key_length);
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if (comparator_.comparator.user_comparator()->Compare(
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Slice(key_ptr, key_length - 8), key.user_key()) == 0) {
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// Correct user key
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const uint64_t tag = DecodeFixed64(key_ptr + key_length - 8);
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switch (static_cast<ValueType>(tag & 0xff)) {
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case kTypeValue: {
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Slice v = GetLengthPrefixedSlice(key_ptr + key_length);
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value->assign(v.data(), v.size());
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return true;
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}
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case kTypeDeletion:
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*s = Status::NotFound(Slice());
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return true;
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}
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}
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}
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return false;
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}
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} // namespace leveldb
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