806e264350
Summary: Rocks accumulates recent writes and deletes in the in-memory memtable. When the memtable is full, it writes the contents on the memtable to a file in L0. This patch removes redundant records at the time of the flush. If there are multiple versions of the same key in the memtable, then only the most recent one is dumped into the output file. The purging of redundant records occur only if the most recent snapshot is earlier than the earliest record in the memtable. Should we switch on this feature by default or should we keep this feature turned off in the default settings? Test Plan: Added test case to db_test.cc Reviewers: sheki, vamsi, emayanke, heyongqiang Reviewed By: sheki CC: leveldb Differential Revision: https://reviews.facebook.net/D8991
114 lines
3.5 KiB
C++
114 lines
3.5 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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#ifndef STORAGE_LEVELDB_DB_MEMTABLE_H_
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#define STORAGE_LEVELDB_DB_MEMTABLE_H_
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#include <string>
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#include "leveldb/db.h"
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#include "db/dbformat.h"
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#include "db/skiplist.h"
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#include "db/version_set.h"
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#include "util/arena.h"
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namespace leveldb {
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class InternalKeyComparator;
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class Mutex;
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class MemTableIterator;
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class MemTable {
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public:
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// MemTables are reference counted. The initial reference count
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// is zero and the caller must call Ref() at least once.
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explicit MemTable(const InternalKeyComparator& comparator,
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int numlevel = 7);
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// Increase reference count.
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void Ref() { ++refs_; }
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// Drop reference count. Delete if no more references exist.
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void Unref() {
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--refs_;
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assert(refs_ >= 0);
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if (refs_ <= 0) {
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delete this;
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}
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}
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// Returns an estimate of the number of bytes of data in use by this
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// data structure.
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//
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// REQUIRES: external synchronization to prevent simultaneous
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// operations on the same MemTable.
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size_t ApproximateMemoryUsage();
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// Return an iterator that yields the contents of the memtable.
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//
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// The caller must ensure that the underlying MemTable remains live
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// while the returned iterator is live. The keys returned by this
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// iterator are internal keys encoded by AppendInternalKey in the
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// db/dbformat.{h,cc} module.
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Iterator* NewIterator();
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// Add an entry into memtable that maps key to value at the
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// specified sequence number and with the specified type.
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// Typically value will be empty if type==kTypeDeletion.
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void Add(SequenceNumber seq, ValueType type,
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const Slice& key,
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const Slice& value);
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// If memtable contains a value for key, store it in *value and return true.
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// If memtable contains a deletion for key, store a NotFound() error
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// in *status and return true.
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// Else, return false.
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bool Get(const LookupKey& key, std::string* value, Status* s);
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// Returns the edits area that is needed for flushing the memtable
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VersionEdit* GetEdits() { return &edit_; }
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// Returns the sequence number of the first element that was inserted
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// into the memtable
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SequenceNumber GetFirstSequenceNumber() { return first_seqno_; }
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private:
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~MemTable(); // Private since only Unref() should be used to delete it
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struct KeyComparator {
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const InternalKeyComparator comparator;
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explicit KeyComparator(const InternalKeyComparator& c) : comparator(c) { }
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int operator()(const char* a, const char* b) const;
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};
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friend class MemTableIterator;
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friend class MemTableBackwardIterator;
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friend class MemTableList;
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typedef SkipList<const char*, KeyComparator> Table;
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KeyComparator comparator_;
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int refs_;
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Arena arena_;
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Table table_;
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// These are used to manage memtable flushes to storage
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bool flush_in_progress_; // started the flush
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bool flush_completed_; // finished the flush
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uint64_t file_number_; // filled up after flush is complete
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// The udpates to be applied to the transaction log when this
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// memtable is flushed to storage.
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VersionEdit edit_;
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// The sequence number of the kv that was inserted first
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SequenceNumber first_seqno_;
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// No copying allowed
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MemTable(const MemTable&);
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void operator=(const MemTable&);
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};
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} // namespace leveldb
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#endif // STORAGE_LEVELDB_DB_MEMTABLE_H_
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