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rocksdb/db/memtable.h

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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
//
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
#pragma once
#include <atomic>
#include <deque>
#include <functional>
#include <memory>
#include <string>
#include <unordered_map>
#include <vector>
#include "db/dbformat.h"
#include "db/range_tombstone_fragmenter.h"
#include "db/read_callback.h"
#include "db/version_edit.h"
#include "memory/allocator.h"
#include "memory/concurrent_arena.h"
#include "monitoring/instrumented_mutex.h"
#include "options/cf_options.h"
#include "rocksdb/db.h"
#include "rocksdb/env.h"
#include "rocksdb/memtablerep.h"
#include "util/dynamic_bloom.h"
#include "util/hash.h"
namespace rocksdb {
class Mutex;
class MemTableIterator;
class MergeContext;
struct ImmutableMemTableOptions {
explicit ImmutableMemTableOptions(const ImmutableCFOptions& ioptions,
const MutableCFOptions& mutable_cf_options);
size_t arena_block_size;
uint32_t memtable_prefix_bloom_bits;
size_t memtable_huge_page_size;
bool memtable_whole_key_filtering;
bool inplace_update_support;
size_t inplace_update_num_locks;
UpdateStatus (*inplace_callback)(char* existing_value,
uint32_t* existing_value_size,
Slice delta_value,
std::string* merged_value);
size_t max_successive_merges;
Statistics* statistics;
MergeOperator* merge_operator;
Logger* info_log;
};
// Batched counters to updated when inserting keys in one write batch.
// In post process of the write batch, these can be updated together.
// Only used in concurrent memtable insert case.
struct MemTablePostProcessInfo {
uint64_t data_size = 0;
uint64_t num_entries = 0;
uint64_t num_deletes = 0;
};
// Note: Many of the methods in this class have comments indicating that
// external synchronization is required as these methods are not thread-safe.
// It is up to higher layers of code to decide how to prevent concurrent
// invokation of these methods. This is usually done by acquiring either
// the db mutex or the single writer thread.
//
// Some of these methods are documented to only require external
// synchronization if this memtable is immutable. Calling MarkImmutable() is
// not sufficient to guarantee immutability. It is up to higher layers of
// code to determine if this MemTable can still be modified by other threads.
// Eg: The Superversion stores a pointer to the current MemTable (that can
// be modified) and a separate list of the MemTables that can no longer be
// written to (aka the 'immutable memtables').
class MemTable {
public:
struct KeyComparator : public MemTableRep::KeyComparator {
const InternalKeyComparator comparator;
explicit KeyComparator(const InternalKeyComparator& c) : comparator(c) { }
virtual int operator()(const char* prefix_len_key1,
const char* prefix_len_key2) const override;
virtual int operator()(const char* prefix_len_key,
const DecodedType& key) const override;
};
// MemTables are reference counted. The initial reference count
// is zero and the caller must call Ref() at least once.
//
// earliest_seq should be the current SequenceNumber in the db such that any
// key inserted into this memtable will have an equal or larger seq number.
// (When a db is first created, the earliest sequence number will be 0).
// If the earliest sequence number is not known, kMaxSequenceNumber may be
// used, but this may prevent some transactions from succeeding until the
// first key is inserted into the memtable.
explicit MemTable(const InternalKeyComparator& comparator,
const ImmutableCFOptions& ioptions,
const MutableCFOptions& mutable_cf_options,
WriteBufferManager* write_buffer_manager,
SequenceNumber earliest_seq, uint32_t column_family_id);
// No copying allowed
MemTable(const MemTable&) = delete;
MemTable& operator=(const MemTable&) = delete;
// Do not delete this MemTable unless Unref() indicates it not in use.
~MemTable();
// Increase reference count.
// REQUIRES: external synchronization to prevent simultaneous
// operations on the same MemTable.
void Ref() { ++refs_; }
// Drop reference count.
// If the refcount goes to zero return this memtable, otherwise return null.
// REQUIRES: external synchronization to prevent simultaneous
// operations on the same MemTable.
MemTable* Unref() {
--refs_;
assert(refs_ >= 0);
if (refs_ <= 0) {
return this;
}
return nullptr;
}
// Returns an estimate of the number of bytes of data in use by this
// data structure.
//
// REQUIRES: external synchronization to prevent simultaneous
// operations on the same MemTable (unless this Memtable is immutable).
size_t ApproximateMemoryUsage();
// As a cheap version of `ApproximateMemoryUsage()`, this function doens't
// require external synchronization. The value may be less accurate though
size_t ApproximateMemoryUsageFast() {
return approximate_memory_usage_.load(std::memory_order_relaxed);
}
// This method heuristically determines if the memtable should continue to
// host more data.
bool ShouldScheduleFlush() const {
return flush_state_.load(std::memory_order_relaxed) == FLUSH_REQUESTED;
}
// Returns true if a flush should be scheduled and the caller should
// be the one to schedule it
bool MarkFlushScheduled() {
auto before = FLUSH_REQUESTED;
return flush_state_.compare_exchange_strong(before, FLUSH_SCHEDULED,
std::memory_order_relaxed,
std::memory_order_relaxed);
}
// Return an iterator that yields the contents of the memtable.
//
// The caller must ensure that the underlying MemTable remains live
// while the returned iterator is live. The keys returned by this
// iterator are internal keys encoded by AppendInternalKey in the
// db/dbformat.{h,cc} module.
//
// By default, it returns an iterator for prefix seek if prefix_extractor
// is configured in Options.
// arena: If not null, the arena needs to be used to allocate the Iterator.
// Calling ~Iterator of the iterator will destroy all the states but
// those allocated in arena.
InternalIterator* NewIterator(const ReadOptions& read_options, Arena* arena);
FragmentedRangeTombstoneIterator* NewRangeTombstoneIterator(
const ReadOptions& read_options, SequenceNumber read_seq);
// Add an entry into memtable that maps key to value at the
// specified sequence number and with the specified type.
// Typically value will be empty if type==kTypeDeletion.
//
// REQUIRES: if allow_concurrent = false, external synchronization to prevent
// simultaneous operations on the same MemTable.
//
// Returns false if MemTableRepFactory::CanHandleDuplicatedKey() is true and
// the <key, seq> already exists.
bool Add(SequenceNumber seq, ValueType type, const Slice& key,
const Slice& value, bool allow_concurrent = false,
MemTablePostProcessInfo* post_process_info = nullptr);
// Used to Get value associated with key or Get Merge Operands associated
// with key.
// If do_merge = true the default behavior which is Get value for key is
// executed. Expected behavior is described right below.
// If memtable contains a value for key, store it in *value and return true.
// If memtable contains a deletion for key, store a NotFound() error
// in *status and return true.
// If memtable contains Merge operation as the most recent entry for a key,
// and the merge process does not stop (not reaching a value or delete),
// prepend the current merge operand to *operands.
// store MergeInProgress in s, and return false.
// Else, return false.
// If any operation was found, its most recent sequence number
// will be stored in *seq on success (regardless of whether true/false is
// returned). Otherwise, *seq will be set to kMaxSequenceNumber.
// On success, *s may be set to OK, NotFound, or MergeInProgress. Any other
// status returned indicates a corruption or other unexpected error.
// If do_merge = false then any Merge Operands encountered for key are simply
// stored in merge_context.operands_list and never actually merged to get a
// final value. The raw Merge Operands are eventually returned to the user.
bool Get(const LookupKey& key, std::string* value, Status* s,
MergeContext* merge_context,
SequenceNumber* max_covering_tombstone_seq, SequenceNumber* seq,
const ReadOptions& read_opts, ReadCallback* callback = nullptr,
bool* is_blob_index = nullptr, bool do_merge = true);
bool Get(const LookupKey& key, std::string* value, Status* s,
MergeContext* merge_context,
SequenceNumber* max_covering_tombstone_seq,
const ReadOptions& read_opts, ReadCallback* callback = nullptr,
bool* is_blob_index = nullptr, bool do_merge = true) {
SequenceNumber seq;
return Get(key, value, s, merge_context, max_covering_tombstone_seq, &seq,
read_opts, callback, is_blob_index, do_merge);
}
// Attempts to update the new_value inplace, else does normal Add
// Pseudocode
// if key exists in current memtable && prev_value is of type kTypeValue
// if new sizeof(new_value) <= sizeof(prev_value)
// update inplace
// else add(key, new_value)
// else add(key, new_value)
//
// REQUIRES: external synchronization to prevent simultaneous
// operations on the same MemTable.
void Update(SequenceNumber seq,
const Slice& key,
const Slice& value);
// If prev_value for key exists, attempts to update it inplace.
// else returns false
// Pseudocode
// if key exists in current memtable && prev_value is of type kTypeValue
// new_value = delta(prev_value)
// if sizeof(new_value) <= sizeof(prev_value)
// update inplace
// else add(key, new_value)
// else return false
//
// REQUIRES: external synchronization to prevent simultaneous
// operations on the same MemTable.
bool UpdateCallback(SequenceNumber seq,
const Slice& key,
const Slice& delta);
// Returns the number of successive merge entries starting from the newest
// entry for the key up to the last non-merge entry or last entry for the
// key in the memtable.
size_t CountSuccessiveMergeEntries(const LookupKey& key);
// Update counters and flush status after inserting a whole write batch
// Used in concurrent memtable inserts.
void BatchPostProcess(const MemTablePostProcessInfo& update_counters) {
num_entries_.fetch_add(update_counters.num_entries,
std::memory_order_relaxed);
data_size_.fetch_add(update_counters.data_size, std::memory_order_relaxed);
if (update_counters.num_deletes != 0) {
num_deletes_.fetch_add(update_counters.num_deletes,
std::memory_order_relaxed);
}
UpdateFlushState();
}
// Get total number of entries in the mem table.
// REQUIRES: external synchronization to prevent simultaneous
// operations on the same MemTable (unless this Memtable is immutable).
uint64_t num_entries() const {
return num_entries_.load(std::memory_order_relaxed);
}
// Get total number of deletes in the mem table.
// REQUIRES: external synchronization to prevent simultaneous
// operations on the same MemTable (unless this Memtable is immutable).
uint64_t num_deletes() const {
return num_deletes_.load(std::memory_order_relaxed);
}
uint64_t get_data_size() const {
return data_size_.load(std::memory_order_relaxed);
}
// Dynamically change the memtable's capacity. If set below the current usage,
// the next key added will trigger a flush. Can only increase size when
// memtable prefix bloom is disabled, since we can't easily allocate more
// space.
void UpdateWriteBufferSize(size_t new_write_buffer_size) {
if (bloom_filter_ == nullptr ||
new_write_buffer_size < write_buffer_size_) {
write_buffer_size_.store(new_write_buffer_size,
std::memory_order_relaxed);
}
}
// Returns the edits area that is needed for flushing the memtable
VersionEdit* GetEdits() { return &edit_; }
// Returns if there is no entry inserted to the mem table.
// REQUIRES: external synchronization to prevent simultaneous
// operations on the same MemTable (unless this Memtable is immutable).
bool IsEmpty() const { return first_seqno_ == 0; }
// Returns the sequence number of the first element that was inserted
// into the memtable.
// REQUIRES: external synchronization to prevent simultaneous
// operations on the same MemTable (unless this Memtable is immutable).
SequenceNumber GetFirstSequenceNumber() {
return first_seqno_.load(std::memory_order_relaxed);
}
// Returns the sequence number that is guaranteed to be smaller than or equal
// to the sequence number of any key that could be inserted into this
// memtable. It can then be assumed that any write with a larger(or equal)
// sequence number will be present in this memtable or a later memtable.
//
// If the earliest sequence number could not be determined,
// kMaxSequenceNumber will be returned.
SequenceNumber GetEarliestSequenceNumber() {
return earliest_seqno_.load(std::memory_order_relaxed);
}
// DB's latest sequence ID when the memtable is created. This number
// may be updated to a more recent one before any key is inserted.
SequenceNumber GetCreationSeq() const { return creation_seq_; }
void SetCreationSeq(SequenceNumber sn) { creation_seq_ = sn; }
// Returns the next active logfile number when this memtable is about to
// be flushed to storage
// REQUIRES: external synchronization to prevent simultaneous
// operations on the same MemTable.
uint64_t GetNextLogNumber() { return mem_next_logfile_number_; }
// Sets the next active logfile number when this memtable is about to
// be flushed to storage
// REQUIRES: external synchronization to prevent simultaneous
// operations on the same MemTable.
void SetNextLogNumber(uint64_t num) { mem_next_logfile_number_ = num; }
// if this memtable contains data from a committed
// two phase transaction we must take note of the
// log which contains that data so we can know
// when to relese that log
void RefLogContainingPrepSection(uint64_t log);
uint64_t GetMinLogContainingPrepSection();
// Notify the underlying storage that no more items will be added.
// REQUIRES: external synchronization to prevent simultaneous
// operations on the same MemTable.
// After MarkImmutable() is called, you should not attempt to
// write anything to this MemTable(). (Ie. do not call Add() or Update()).
void MarkImmutable() {
table_->MarkReadOnly();
mem_tracker_.DoneAllocating();
}
// Notify the underlying storage that all data it contained has been
// persisted.
// REQUIRES: external synchronization to prevent simultaneous
// operations on the same MemTable.
void MarkFlushed() {
table_->MarkFlushed();
}
// return true if the current MemTableRep supports merge operator.
bool IsMergeOperatorSupported() const {
return table_->IsMergeOperatorSupported();
}
// return true if the current MemTableRep supports snapshots.
// inplace update prevents snapshots,
bool IsSnapshotSupported() const {
return table_->IsSnapshotSupported() && !moptions_.inplace_update_support;
}
struct MemTableStats {
uint64_t size;
uint64_t count;
};
MemTableStats ApproximateStats(const Slice& start_ikey,
const Slice& end_ikey);
// Get the lock associated for the key
port::RWMutex* GetLock(const Slice& key);
const InternalKeyComparator& GetInternalKeyComparator() const {
return comparator_.comparator;
}
const ImmutableMemTableOptions* GetImmutableMemTableOptions() const {
return &moptions_;
}
uint64_t ApproximateOldestKeyTime() const {
return oldest_key_time_.load(std::memory_order_relaxed);
}
// REQUIRES: db_mutex held.
void SetID(uint64_t id) { id_ = id; }
uint64_t GetID() const { return id_; }
void SetFlushCompleted(bool completed) { flush_completed_ = completed; }
uint64_t GetFileNumber() const { return file_number_; }
void SetFileNumber(uint64_t file_num) { file_number_ = file_num; }
void SetFlushInProgress(bool in_progress) {
flush_in_progress_ = in_progress;
}
private:
enum FlushStateEnum { FLUSH_NOT_REQUESTED, FLUSH_REQUESTED, FLUSH_SCHEDULED };
friend class MemTableIterator;
friend class MemTableBackwardIterator;
friend class MemTableList;
KeyComparator comparator_;
const ImmutableMemTableOptions moptions_;
int refs_;
const size_t kArenaBlockSize;
AllocTracker mem_tracker_;
ConcurrentArena arena_;
std::unique_ptr<MemTableRep> table_;
std::unique_ptr<MemTableRep> range_del_table_;
std::atomic_bool is_range_del_table_empty_;
// Total data size of all data inserted
std::atomic<uint64_t> data_size_;
std::atomic<uint64_t> num_entries_;
std::atomic<uint64_t> num_deletes_;
// Dynamically changeable memtable option
std::atomic<size_t> write_buffer_size_;
// These are used to manage memtable flushes to storage
bool flush_in_progress_; // started the flush
bool flush_completed_; // finished the flush
uint64_t file_number_; // filled up after flush is complete
// The updates to be applied to the transaction log when this
// memtable is flushed to storage.
VersionEdit edit_;
// The sequence number of the kv that was inserted first
std::atomic<SequenceNumber> first_seqno_;
// The db sequence number at the time of creation or kMaxSequenceNumber
// if not set.
std::atomic<SequenceNumber> earliest_seqno_;
SequenceNumber creation_seq_;
// The log files earlier than this number can be deleted.
uint64_t mem_next_logfile_number_;
// the earliest log containing a prepared section
// which has been inserted into this memtable.
std::atomic<uint64_t> min_prep_log_referenced_;
// rw locks for inplace updates
std::vector<port::RWMutex> locks_;
const SliceTransform* const prefix_extractor_;
std::unique_ptr<DynamicBloom> bloom_filter_;
std::atomic<FlushStateEnum> flush_state_;
Env* env_;
// Extract sequential insert prefixes.
const SliceTransform* insert_with_hint_prefix_extractor_;
// Insert hints for each prefix.
std::unordered_map<Slice, void*, SliceHasher> insert_hints_;
// Timestamp of oldest key
std::atomic<uint64_t> oldest_key_time_;
// Memtable id to track flush.
uint64_t id_ = 0;
// Sequence number of the atomic flush that is responsible for this memtable.
// The sequence number of atomic flush is a seq, such that no writes with
// sequence numbers greater than or equal to seq are flushed, while all
// writes with sequence number smaller than seq are flushed.
SequenceNumber atomic_flush_seqno_;
// keep track of memory usage in table_, arena_, and range_del_table_.
// Gets refrshed inside `ApproximateMemoryUsage()` or `ShouldFlushNow`
std::atomic<uint64_t> approximate_memory_usage_;
// Returns a heuristic flush decision
bool ShouldFlushNow();
// Updates flush_state_ using ShouldFlushNow()
void UpdateFlushState();
void UpdateOldestKeyTime();
};
extern const char* EncodeKey(std::string* scratch, const Slice& target);
} // namespace rocksdb