6acbe0fc45
Summary: Merge multiple multiple memtables in memory before writing it out to a file in L0. There is a new config parameter min_write_buffer_number_to_merge that specifies the number of write buffers that should be merged together to a single file in storage. The system will not flush wrte buffers to storage unless at least these many buffers have accumulated in memory. The default value of this new parameter is 1, which means that a write buffer will be immediately flushed to disk as soon it is ready. Test Plan: make check Differential Revision: https://reviews.facebook.net/D11241
98 lines
2.8 KiB
C++
98 lines
2.8 KiB
C++
// Copyright (c) 2012 Facebook.
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#ifndef STORAGE_LEVELDB_DB_MEMTABLELIST_H_
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#define STORAGE_LEVELDB_DB_MEMTABLELIST_H_
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#include <string>
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#include <list>
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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 "util/arena.h"
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#include "memtable.h"
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namespace leveldb {
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class InternalKeyComparator;
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class Mutex;
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class MemTableListIterator;
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//
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// This class stores references to all the immutable memtables.
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// The memtables are flushed to L0 as soon as possible and in
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// any order. If there are more than one immutable memtable, their
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// flushes can occur concurrently. However, they are 'committed'
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// to the manifest in FIFO order to maintain correctness and
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// recoverability from a crash.
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//
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class MemTableList {
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public:
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// A list of memtables.
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MemTableList() : size_(0), num_flush_not_started_(0),
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commit_in_progress_(false) {
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imm_flush_needed.Release_Store(nullptr);
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}
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~MemTableList() {};
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// so that backgrund threads can detect non-nullptr pointer to
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// determine whether this is anything more to start flushing.
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port::AtomicPointer imm_flush_needed;
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// Increase reference count on all underling memtables
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void RefAll();
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// Drop reference count on all underling memtables
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void UnrefAll();
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// Returns the total number of memtables in the list
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int size();
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// Returns true if there is at least one memtable on which flush has
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// not yet started.
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bool IsFlushPending(int min_write_buffer_number_to_merge);
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// Returns the earliest memtables that needs to be flushed.
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void PickMemtablesToFlush(std::vector<MemTable*>* mems);
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// Commit a successful flush in the manifest file
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Status InstallMemtableFlushResults(const std::vector<MemTable*> &m,
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VersionSet* vset, Status flushStatus,
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port::Mutex* mu, Logger* info_log,
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uint64_t file_number,
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std::set<uint64_t>& pending_outputs);
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// New memtables are inserted at the front of the list.
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// Takes ownership of the referenced held on *m by the caller of Add().
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void Add(MemTable* m);
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// Returns an estimate of the number of bytes of data in use.
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size_t ApproximateMemoryUsage();
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// Search all the memtables starting from the most recent one.
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// Return the most recent value found, if any.
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bool Get(const LookupKey& key, std::string* value, Status* s,
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const Options& options);
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// Returns the list of underlying memtables.
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void GetMemTables(std::vector<MemTable*>* list);
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// Copying allowed
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// MemTableList(const MemTableList&);
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// void operator=(const MemTableList&);
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private:
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std::list<MemTable*> memlist_;
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int size_;
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// the number of elements that still need flushing
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int num_flush_not_started_;
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// committing in progress
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bool commit_in_progress_;
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};
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} // namespace leveldb
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#endif // STORAGE_LEVELDB_DB_MEMTABLELIST_H_
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