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rocksdb/db/memtable_list.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).
//
#pragma once
#include <deque>
#include <limits>
#include <list>
#include <set>
#include <string>
#include <vector>
#include "db/dbformat.h"
#include "db/logs_with_prep_tracker.h"
#include "db/memtable.h"
#include "db/range_del_aggregator.h"
#include "file/filename.h"
#include "logging/log_buffer.h"
#include "monitoring/instrumented_mutex.h"
#include "rocksdb/db.h"
#include "rocksdb/iterator.h"
#include "rocksdb/options.h"
#include "rocksdb/types.h"
#include "util/autovector.h"
namespace rocksdb {
class ColumnFamilyData;
class InternalKeyComparator;
class InstrumentedMutex;
class MergeIteratorBuilder;
class MemTableList;
// keeps a list of immutable memtables in a vector. the list is immutable
// if refcount is bigger than one. It is used as a state for Get() and
// Iterator code paths
//
// This class is not thread-safe. External synchronization is required
// (such as holding the db mutex or being on the write thread).
class MemTableListVersion {
public:
explicit MemTableListVersion(size_t* parent_memtable_list_memory_usage,
MemTableListVersion* old = nullptr);
explicit MemTableListVersion(size_t* parent_memtable_list_memory_usage,
int max_write_buffer_number_to_maintain,
int64_t max_write_buffer_size_to_maintain);
void Ref();
void Unref(autovector<MemTable*>* to_delete = nullptr);
// Search all the memtables starting from the most recent one.
// Return the most recent value found, if any.
//
// If any operation was found for this key, 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.
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 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) {
SequenceNumber seq;
return Get(key, value, s, merge_context, max_covering_tombstone_seq, &seq,
read_opts, callback, is_blob_index);
}
void MultiGet(const ReadOptions& read_options, MultiGetRange* range,
ReadCallback* callback, bool* is_blob);
// Returns all the merge operands corresponding to the key by searching all
// memtables starting from the most recent one.
bool GetMergeOperands(const LookupKey& key, Status* s,
MergeContext* merge_context,
SequenceNumber* max_covering_tombstone_seq,
const ReadOptions& read_opts);
// Similar to Get(), but searches the Memtable history of memtables that
// have already been flushed. Should only be used from in-memory only
// queries (such as Transaction validation) as the history may contain
// writes that are also present in the SST files.
bool GetFromHistory(const LookupKey& key, std::string* value, Status* s,
MergeContext* merge_context,
SequenceNumber* max_covering_tombstone_seq,
SequenceNumber* seq, const ReadOptions& read_opts,
bool* is_blob_index = nullptr);
bool GetFromHistory(const LookupKey& key, std::string* value, Status* s,
MergeContext* merge_context,
SequenceNumber* max_covering_tombstone_seq,
const ReadOptions& read_opts,
bool* is_blob_index = nullptr) {
SequenceNumber seq;
return GetFromHistory(key, value, s, merge_context,
max_covering_tombstone_seq, &seq, read_opts,
is_blob_index);
}
Status AddRangeTombstoneIterators(const ReadOptions& read_opts, Arena* arena,
RangeDelAggregator* range_del_agg);
void AddIterators(const ReadOptions& options,
std::vector<InternalIterator*>* iterator_list,
Arena* arena);
void AddIterators(const ReadOptions& options,
MergeIteratorBuilder* merge_iter_builder);
uint64_t GetTotalNumEntries() const;
uint64_t GetTotalNumDeletes() const;
MemTable::MemTableStats ApproximateStats(const Slice& start_ikey,
const Slice& end_ikey);
// Returns the value of MemTable::GetEarliestSequenceNumber() on the most
// recent MemTable in this list or kMaxSequenceNumber if the list is empty.
// If include_history=true, will also search Memtables in MemTableList
// History.
SequenceNumber GetEarliestSequenceNumber(bool include_history = false) const;
private:
friend class MemTableList;
friend Status InstallMemtableAtomicFlushResults(
const autovector<MemTableList*>* imm_lists,
const autovector<ColumnFamilyData*>& cfds,
const autovector<const MutableCFOptions*>& mutable_cf_options_list,
const autovector<const autovector<MemTable*>*>& mems_list,
VersionSet* vset, InstrumentedMutex* mu,
const autovector<FileMetaData*>& file_meta,
autovector<MemTable*>* to_delete, Directory* db_directory,
LogBuffer* log_buffer);
// REQUIRE: m is an immutable memtable
void Add(MemTable* m, autovector<MemTable*>* to_delete);
// REQUIRE: m is an immutable memtable
void Remove(MemTable* m, autovector<MemTable*>* to_delete);
void TrimHistory(autovector<MemTable*>* to_delete, size_t usage);
bool GetFromList(std::list<MemTable*>* list, 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);
void AddMemTable(MemTable* m);
void UnrefMemTable(autovector<MemTable*>* to_delete, MemTable* m);
// Calculate the total amount of memory used by memlist_ and memlist_history_
// excluding the last MemTable in memlist_history_. The reason for excluding
// the last MemTable is to see if dropping the last MemTable will keep total
// memory usage above or equal to max_write_buffer_size_to_maintain_
size_t ApproximateMemoryUsageExcludingLast();
bool MemtableLimitExceeded(size_t usage);
// Immutable MemTables that have not yet been flushed.
std::list<MemTable*> memlist_;
// MemTables that have already been flushed
// (used during Transaction validation)
std::list<MemTable*> memlist_history_;
// Maximum number of MemTables to keep in memory (including both flushed
const int max_write_buffer_number_to_maintain_;
// Maximum size of MemTables to keep in memory (including both flushed
// and not-yet-flushed tables).
const int64_t max_write_buffer_size_to_maintain_;
int refs_ = 0;
size_t* parent_memtable_list_memory_usage_;
};
// This class stores references to all the immutable memtables.
// The memtables are flushed to L0 as soon as possible and in
// any order. If there are more than one immutable memtable, their
// flushes can occur concurrently. However, they are 'committed'
// to the manifest in FIFO order to maintain correctness and
// recoverability from a crash.
//
//
// Other than imm_flush_needed and imm_trim_needed, this class is not
// thread-safe and requires external synchronization (such as holding the db
// mutex or being on the write thread.)
class MemTableList {
public:
// A list of memtables.
explicit MemTableList(int min_write_buffer_number_to_merge,
int max_write_buffer_number_to_maintain,
int64_t max_write_buffer_size_to_maintain)
: imm_flush_needed(false),
imm_trim_needed(false),
min_write_buffer_number_to_merge_(min_write_buffer_number_to_merge),
current_(new MemTableListVersion(&current_memory_usage_,
max_write_buffer_number_to_maintain,
max_write_buffer_size_to_maintain)),
num_flush_not_started_(0),
commit_in_progress_(false),
flush_requested_(false),
current_memory_usage_(0),
current_memory_usage_excluding_last_(0) {
current_->Ref();
}
// Should not delete MemTableList without making sure MemTableList::current()
// is Unref()'d.
~MemTableList() {}
MemTableListVersion* current() const { return current_; }
// so that background threads can detect non-nullptr pointer to
// determine whether there is anything more to start flushing.
std::atomic<bool> imm_flush_needed;
std::atomic<bool> imm_trim_needed;
// Returns the total number of memtables in the list that haven't yet
// been flushed and logged.
int NumNotFlushed() const;
// Returns total number of memtables in the list that have been
// completely flushed and logged.
int NumFlushed() const;
// Returns true if there is at least one memtable on which flush has
// not yet started.
bool IsFlushPending() const;
// Returns the earliest memtables that needs to be flushed. The returned
// memtables are guaranteed to be in the ascending order of created time.
void PickMemtablesToFlush(const uint64_t* max_memtable_id,
autovector<MemTable*>* mems);
// Reset status of the given memtable list back to pending state so that
// they can get picked up again on the next round of flush.
void RollbackMemtableFlush(const autovector<MemTable*>& mems,
uint64_t file_number);
// Try commit a successful flush in the manifest file. It might just return
// Status::OK letting a concurrent flush to do the actual the recording.
Status TryInstallMemtableFlushResults(
ColumnFamilyData* cfd, const MutableCFOptions& mutable_cf_options,
const autovector<MemTable*>& m, LogsWithPrepTracker* prep_tracker,
VersionSet* vset, InstrumentedMutex* mu, uint64_t file_number,
autovector<MemTable*>* to_delete, Directory* db_directory,
LogBuffer* log_buffer);
// New memtables are inserted at the front of the list.
// Takes ownership of the referenced held on *m by the caller of Add().
void Add(MemTable* m, autovector<MemTable*>* to_delete);
// Returns an estimate of the number of bytes of data in use.
size_t ApproximateMemoryUsage();
// Returns the cached current_memory_usage_excluding_last_ value
size_t ApproximateMemoryUsageExcludingLast();
// Update current_memory_usage_excluding_last_ from MemtableListVersion
void UpdateMemoryUsageExcludingLast();
// `usage` is the current size of the mutable Memtable. When
// max_write_buffer_size_to_maintain is used, total size of mutable and
// immutable memtables is checked against it to decide whether to trim
// memtable list.
void TrimHistory(autovector<MemTable*>* to_delete, size_t usage);
// Returns an estimate of the number of bytes of data used by
// the unflushed mem-tables.
size_t ApproximateUnflushedMemTablesMemoryUsage();
// Returns an estimate of the timestamp of the earliest key.
uint64_t ApproximateOldestKeyTime() const;
// Request a flush of all existing memtables to storage. This will
// cause future calls to IsFlushPending() to return true if this list is
// non-empty (regardless of the min_write_buffer_number_to_merge
// parameter). This flush request will persist until the next time
// PickMemtablesToFlush() is called.
void FlushRequested() { flush_requested_ = true; }
bool HasFlushRequested() { return flush_requested_; }
// Returns true if a trim history should be scheduled and the caller should
// be the one to schedule it
bool MarkTrimHistoryNeeded() {
auto expected = false;
return imm_trim_needed.compare_exchange_strong(
expected, true, std::memory_order_relaxed, std::memory_order_relaxed);
}
void ResetTrimHistoryNeeded() {
auto expected = true;
imm_trim_needed.compare_exchange_strong(
expected, false, std::memory_order_relaxed, std::memory_order_relaxed);
}
// Copying allowed
// MemTableList(const MemTableList&);
// void operator=(const MemTableList&);
size_t* current_memory_usage() { return &current_memory_usage_; }
// Returns the min log containing the prep section after memtables listsed in
// `memtables_to_flush` are flushed and their status is persisted in manifest.
uint64_t PrecomputeMinLogContainingPrepSection(
const autovector<MemTable*>& memtables_to_flush);
uint64_t GetEarliestMemTableID() const {
auto& memlist = current_->memlist_;
if (memlist.empty()) {
return std::numeric_limits<uint64_t>::max();
}
return memlist.back()->GetID();
}
uint64_t GetLatestMemTableID() const {
auto& memlist = current_->memlist_;
if (memlist.empty()) {
return 0;
}
return memlist.front()->GetID();
}
void AssignAtomicFlushSeq(const SequenceNumber& seq) {
const auto& memlist = current_->memlist_;
// Scan the memtable list from new to old
for (auto it = memlist.begin(); it != memlist.end(); ++it) {
MemTable* mem = *it;
if (mem->atomic_flush_seqno_ == kMaxSequenceNumber) {
mem->atomic_flush_seqno_ = seq;
} else {
// Earlier memtables must have been assigned a atomic flush seq, no
// need to continue scan.
break;
}
}
}
// Used only by DBImplSecondary during log replay.
// Remove memtables whose data were written before the WAL with log_number
// was created, i.e. mem->GetNextLogNumber() <= log_number. The memtables are
// not freed, but put into a vector for future deref and reclamation.
void RemoveOldMemTables(uint64_t log_number,
autovector<MemTable*>* to_delete);
private:
friend Status InstallMemtableAtomicFlushResults(
const autovector<MemTableList*>* imm_lists,
const autovector<ColumnFamilyData*>& cfds,
const autovector<const MutableCFOptions*>& mutable_cf_options_list,
const autovector<const autovector<MemTable*>*>& mems_list,
VersionSet* vset, InstrumentedMutex* mu,
const autovector<FileMetaData*>& file_meta,
autovector<MemTable*>* to_delete, Directory* db_directory,
LogBuffer* log_buffer);
// DB mutex held
void InstallNewVersion();
const int min_write_buffer_number_to_merge_;
MemTableListVersion* current_;
// the number of elements that still need flushing
int num_flush_not_started_;
// committing in progress
bool commit_in_progress_;
// Requested a flush of memtables to storage. It's possible to request that
// a subset of memtables be flushed.
bool flush_requested_;
// The current memory usage.
size_t current_memory_usage_;
std::atomic<size_t> current_memory_usage_excluding_last_;
};
// Installs memtable atomic flush results.
// In most cases, imm_lists is nullptr, and the function simply uses the
// immutable memtable lists associated with the cfds. There are unit tests that
// installs flush results for external immutable memtable lists other than the
// cfds' own immutable memtable lists, e.g. MemTableLIstTest. In this case,
// imm_lists parameter is not nullptr.
extern Status InstallMemtableAtomicFlushResults(
const autovector<MemTableList*>* imm_lists,
const autovector<ColumnFamilyData*>& cfds,
const autovector<const MutableCFOptions*>& mutable_cf_options_list,
const autovector<const autovector<MemTable*>*>& mems_list, VersionSet* vset,
InstrumentedMutex* mu, const autovector<FileMetaData*>& file_meta,
autovector<MemTable*>* to_delete, Directory* db_directory,
LogBuffer* log_buffer);
} // namespace rocksdb