rocksdb/db/column_family.h
Igor Canadi a2bb7c3c33 Push- instead of pull-model for managing Write stalls
Summary:
Introducing WriteController, which is a source of truth about per-DB write delays. Let's define an DB epoch as a period where there are no flushes and compactions (i.e. new epoch is started when flush or compaction finishes). Each epoch can either:
* proceed with all writes without delay
* delay all writes by fixed time
* stop all writes

The three modes are recomputed at each epoch change (flush, compaction), rather than on every write (which is currently the case).

When we have a lot of column families, our current pull behavior adds a big overhead, since we need to loop over every column family for every write. With new push model, overhead on Write code-path is minimal.

This is just the start. Next step is to also take care of stalls introduced by slow memtable flushes. The final goal is to eliminate function MakeRoomForWrite(), which currently needs to be called for every column family by every write.

Test Plan: make check for now. I'll add some unit tests later. Also, perf test.

Reviewers: dhruba, yhchiang, MarkCallaghan, sdong, ljin

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D22791
2014-09-08 11:20:25 -07:00

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// Copyright (c) 2013, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same 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 <unordered_map>
#include <string>
#include <vector>
#include <atomic>
#include "rocksdb/options.h"
#include "rocksdb/db.h"
#include "rocksdb/env.h"
#include "db/memtable_list.h"
#include "db/write_batch_internal.h"
#include "db/write_controller.h"
#include "db/table_cache.h"
#include "util/thread_local.h"
namespace rocksdb {
class Version;
class VersionSet;
class MemTable;
class MemTableListVersion;
class CompactionPicker;
class Compaction;
class InternalKey;
class InternalStats;
class ColumnFamilyData;
class DBImpl;
class LogBuffer;
// ColumnFamilyHandleImpl is the class that clients use to access different
// column families. It has non-trivial destructor, which gets called when client
// is done using the column family
class ColumnFamilyHandleImpl : public ColumnFamilyHandle {
public:
// create while holding the mutex
ColumnFamilyHandleImpl(ColumnFamilyData* cfd, DBImpl* db, port::Mutex* mutex);
// destroy without mutex
virtual ~ColumnFamilyHandleImpl();
virtual ColumnFamilyData* cfd() const { return cfd_; }
virtual uint32_t GetID() const;
private:
ColumnFamilyData* cfd_;
DBImpl* db_;
port::Mutex* mutex_;
};
// Does not ref-count ColumnFamilyData
// We use this dummy ColumnFamilyHandleImpl because sometimes MemTableInserter
// calls DBImpl methods. When this happens, MemTableInserter need access to
// ColumnFamilyHandle (same as the client would need). In that case, we feed
// MemTableInserter dummy ColumnFamilyHandle and enable it to call DBImpl
// methods
class ColumnFamilyHandleInternal : public ColumnFamilyHandleImpl {
public:
ColumnFamilyHandleInternal()
: ColumnFamilyHandleImpl(nullptr, nullptr, nullptr) {}
void SetCFD(ColumnFamilyData* cfd) { internal_cfd_ = cfd; }
virtual ColumnFamilyData* cfd() const override { return internal_cfd_; }
private:
ColumnFamilyData* internal_cfd_;
};
// holds references to memtable, all immutable memtables and version
struct SuperVersion {
MemTable* mem;
MemTableListVersion* imm;
Version* current;
std::atomic<uint32_t> refs;
// We need to_delete because during Cleanup(), imm->Unref() returns
// all memtables that we need to free through this vector. We then
// delete all those memtables outside of mutex, during destruction
autovector<MemTable*> to_delete;
// Version number of the current SuperVersion
uint64_t version_number;
port::Mutex* db_mutex;
// should be called outside the mutex
SuperVersion() = default;
~SuperVersion();
SuperVersion* Ref();
bool Unref();
// call these two methods with db mutex held
// Cleanup unrefs mem, imm and current. Also, it stores all memtables
// that needs to be deleted in to_delete vector. Unrefing those
// objects needs to be done in the mutex
void Cleanup();
void Init(MemTable* new_mem, MemTableListVersion* new_imm,
Version* new_current);
// The value of dummy is not actually used. kSVInUse takes its address as a
// mark in the thread local storage to indicate the SuperVersion is in use
// by thread. This way, the value of kSVInUse is guaranteed to have no
// conflict with SuperVersion object address and portable on different
// platform.
static int dummy;
static void* const kSVInUse;
static void* const kSVObsolete;
};
extern ColumnFamilyOptions SanitizeOptions(const InternalKeyComparator* icmp,
const ColumnFamilyOptions& src);
class ColumnFamilySet;
// This class keeps all the data that a column family needs. It's mosly dumb and
// used just to provide access to metadata.
// Most methods require DB mutex held, unless otherwise noted
class ColumnFamilyData {
public:
~ColumnFamilyData();
// thread-safe
uint32_t GetID() const { return id_; }
// thread-safe
const std::string& GetName() const { return name_; }
void Ref() { ++refs_; }
// will just decrease reference count to 0, but will not delete it. returns
// true if the ref count was decreased to zero. in that case, it can be
// deleted by the caller immediatelly, or later, by calling
// FreeDeadColumnFamilies()
bool Unref() {
assert(refs_ > 0);
return --refs_ == 0;
}
// This can only be called from single-threaded VersionSet::LogAndApply()
// After dropping column family no other operation on that column family
// will be executed. All the files and memory will be, however, kept around
// until client drops the column family handle. That way, client can still
// access data from dropped column family.
// Column family can be dropped and still alive. In that state:
// *) Column family is not included in the iteration.
// *) Compaction and flush is not executed on the dropped column family.
// *) Client can continue writing and reading from column family. However, all
// writes stay in the current memtable.
// When the dropped column family is unreferenced, then we:
// *) delete all memory associated with that column family
// *) delete all the files associated with that column family
void SetDropped() {
// can't drop default CF
assert(id_ != 0);
dropped_ = true;
write_controller_token_.reset();
}
bool IsDropped() const { return dropped_; }
// thread-safe
int NumberLevels() const { return options_.num_levels; }
void SetLogNumber(uint64_t log_number) { log_number_ = log_number; }
uint64_t GetLogNumber() const { return log_number_; }
// TODO(ljin): make this API thread-safe once we allow updating options_
const Options* options() const { return &options_; }
// thread-safe
const EnvOptions* soptions() const;
const ImmutableCFOptions* ioptions() const { return &ioptions_; }
InternalStats* internal_stats() { return internal_stats_.get(); }
MemTableList* imm() { return &imm_; }
MemTable* mem() { return mem_; }
Version* current() { return current_; }
Version* dummy_versions() { return dummy_versions_; }
void SetMemtable(MemTable* new_mem) { mem_ = new_mem; }
void SetCurrent(Version* current);
void CreateNewMemtable();
TableCache* table_cache() const { return table_cache_.get(); }
// See documentation in compaction_picker.h
Compaction* PickCompaction(LogBuffer* log_buffer);
Compaction* CompactRange(int input_level, int output_level,
uint32_t output_path_id, const InternalKey* begin,
const InternalKey* end,
InternalKey** compaction_end);
CompactionPicker* compaction_picker() { return compaction_picker_.get(); }
// thread-safe
const Comparator* user_comparator() const {
return internal_comparator_.user_comparator();
}
// thread-safe
const InternalKeyComparator& internal_comparator() const {
return internal_comparator_;
}
SuperVersion* GetSuperVersion() { return super_version_; }
// thread-safe
// Return a already referenced SuperVersion to be used safely.
SuperVersion* GetReferencedSuperVersion(port::Mutex* db_mutex);
// thread-safe
// Get SuperVersion stored in thread local storage. If it does not exist,
// get a reference from a current SuperVersion.
SuperVersion* GetThreadLocalSuperVersion(port::Mutex* db_mutex);
// Try to return SuperVersion back to thread local storage. Retrun true on
// success and false on failure. It fails when the thread local storage
// contains anything other than SuperVersion::kSVInUse flag.
bool ReturnThreadLocalSuperVersion(SuperVersion* sv);
// thread-safe
uint64_t GetSuperVersionNumber() const {
return super_version_number_.load();
}
// will return a pointer to SuperVersion* if previous SuperVersion
// if its reference count is zero and needs deletion or nullptr if not
// As argument takes a pointer to allocated SuperVersion to enable
// the clients to allocate SuperVersion outside of mutex.
SuperVersion* InstallSuperVersion(SuperVersion* new_superversion,
port::Mutex* db_mutex);
void ResetThreadLocalSuperVersions();
private:
friend class ColumnFamilySet;
ColumnFamilyData(uint32_t id, const std::string& name,
Version* dummy_versions, Cache* table_cache,
const ColumnFamilyOptions& options,
const DBOptions* db_options, const EnvOptions& env_options,
ColumnFamilySet* column_family_set);
// Recalculate some small conditions, which are changed only during
// compaction, adding new memtable and/or
// recalculation of compaction score. These values are used in
// DBImpl::MakeRoomForWrite function to decide, if it need to make
// a write stall
void RecalculateWriteStallConditions();
uint32_t id_;
const std::string name_;
Version* dummy_versions_; // Head of circular doubly-linked list of versions.
Version* current_; // == dummy_versions->prev_
int refs_; // outstanding references to ColumnFamilyData
bool dropped_; // true if client dropped it
const InternalKeyComparator internal_comparator_;
const Options options_;
const ImmutableCFOptions ioptions_;
std::unique_ptr<TableCache> table_cache_;
std::unique_ptr<InternalStats> internal_stats_;
MemTable* mem_;
MemTableList imm_;
SuperVersion* super_version_;
// An ordinal representing the current SuperVersion. Updated by
// InstallSuperVersion(), i.e. incremented every time super_version_
// changes.
std::atomic<uint64_t> super_version_number_;
// Thread's local copy of SuperVersion pointer
// This needs to be destructed before mutex_
std::unique_ptr<ThreadLocalPtr> local_sv_;
// pointers for a circular linked list. we use it to support iterations
// that can be concurrent with writes
ColumnFamilyData* next_;
ColumnFamilyData* prev_;
// This is the earliest log file number that contains data from this
// Column Family. All earlier log files must be ignored and not
// recovered from
uint64_t log_number_;
// An object that keeps all the compaction stats
// and picks the next compaction
std::unique_ptr<CompactionPicker> compaction_picker_;
ColumnFamilySet* column_family_set_;
std::unique_ptr<WriteControllerToken> write_controller_token_;
};
// ColumnFamilySet has interesting thread-safety requirements
// * CreateColumnFamily() or RemoveColumnFamily() -- need to protect by DB
// mutex. Inside, column_family_data_ and column_families_ will be protected
// by Lock() and Unlock(). CreateColumnFamily() should ONLY be called from
// VersionSet::LogAndApply() in the normal runtime. It is also called
// during Recovery and in DumpManifest(). RemoveColumnFamily() is called
// from ColumnFamilyData destructor
// * Iteration -- hold DB mutex, but you can release it in the body of
// iteration. If you release DB mutex in body, reference the column
// family before the mutex and unreference after you unlock, since the column
// family might get dropped when the DB mutex is released
// * GetDefault() -- thread safe
// * GetColumnFamily() -- either inside of DB mutex or call Lock() <-> Unlock()
// * GetNextColumnFamilyID(), GetMaxColumnFamily(), UpdateMaxColumnFamily(),
// NumberOfColumnFamilies -- inside of DB mutex
class ColumnFamilySet {
public:
// ColumnFamilySet supports iteration
class iterator {
public:
explicit iterator(ColumnFamilyData* cfd)
: current_(cfd) {}
iterator& operator++() {
// dummy is never dead or dropped, so this will never be infinite
do {
current_ = current_->next_;
} while (current_->refs_ == 0 || current_->IsDropped());
return *this;
}
bool operator!=(const iterator& other) {
return this->current_ != other.current_;
}
ColumnFamilyData* operator*() { return current_; }
private:
ColumnFamilyData* current_;
};
ColumnFamilySet(const std::string& dbname, const DBOptions* db_options,
const EnvOptions& env_options, Cache* table_cache,
WriteController* write_controller);
~ColumnFamilySet();
ColumnFamilyData* GetDefault() const;
// GetColumnFamily() calls return nullptr if column family is not found
ColumnFamilyData* GetColumnFamily(uint32_t id) const;
ColumnFamilyData* GetColumnFamily(const std::string& name) const;
// this call will return the next available column family ID. it guarantees
// that there is no column family with id greater than or equal to the
// returned value in the current running instance or anytime in RocksDB
// instance history.
uint32_t GetNextColumnFamilyID();
uint32_t GetMaxColumnFamily();
void UpdateMaxColumnFamily(uint32_t new_max_column_family);
size_t NumberOfColumnFamilies() const;
ColumnFamilyData* CreateColumnFamily(const std::string& name, uint32_t id,
Version* dummy_version,
const ColumnFamilyOptions& options);
iterator begin() { return iterator(dummy_cfd_->next_); }
iterator end() { return iterator(dummy_cfd_); }
void Lock();
void Unlock();
// REQUIRES: DB mutex held
// Don't call while iterating over ColumnFamilySet
void FreeDeadColumnFamilies();
private:
friend class ColumnFamilyData;
// helper function that gets called from cfd destructor
// REQUIRES: DB mutex held
void RemoveColumnFamily(ColumnFamilyData* cfd);
// column_families_ and column_family_data_ need to be protected:
// * when mutating: 1. DB mutex locked first, 2. spinlock locked second
// * when reading, either: 1. lock DB mutex, or 2. lock spinlock
// (if both, respect the ordering to avoid deadlock!)
std::unordered_map<std::string, uint32_t> column_families_;
std::unordered_map<uint32_t, ColumnFamilyData*> column_family_data_;
uint32_t max_column_family_;
ColumnFamilyData* dummy_cfd_;
// We don't hold the refcount here, since default column family always exists
// We are also not responsible for cleaning up default_cfd_cache_. This is
// just a cache that makes common case (accessing default column family)
// faster
ColumnFamilyData* default_cfd_cache_;
const std::string db_name_;
const DBOptions* const db_options_;
const EnvOptions env_options_;
Cache* table_cache_;
WriteController* write_controller_;
std::atomic_flag spin_lock_;
};
// We use ColumnFamilyMemTablesImpl to provide WriteBatch a way to access
// memtables of different column families (specified by ID in the write batch)
class ColumnFamilyMemTablesImpl : public ColumnFamilyMemTables {
public:
explicit ColumnFamilyMemTablesImpl(ColumnFamilySet* column_family_set)
: column_family_set_(column_family_set), current_(nullptr) {}
// sets current_ to ColumnFamilyData with column_family_id
// returns false if column family doesn't exist
bool Seek(uint32_t column_family_id) override;
// Returns log number of the selected column family
uint64_t GetLogNumber() const override;
// REQUIRES: Seek() called first
virtual MemTable* GetMemTable() const override;
// Returns options for selected column family
// REQUIRES: Seek() called first
virtual const Options* GetOptions() const override;
// Returns column family handle for the selected column family
virtual ColumnFamilyHandle* GetColumnFamilyHandle() override;
private:
ColumnFamilySet* column_family_set_;
ColumnFamilyData* current_;
ColumnFamilyHandleInternal handle_;
};
extern uint32_t GetColumnFamilyID(ColumnFamilyHandle* column_family);
} // namespace rocksdb