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145 lines
4.7 KiB
145 lines
4.7 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& cmp) |
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: comparator_(cmp), |
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refs_(0), |
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table_(comparator_, &arena_) { |
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} |
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MemTable::~MemTable() { |
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assert(refs_ == 0); |
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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) : iter_(table) { } |
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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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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), |
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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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