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/**
* Copyright (C) 2014 MongoDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the GNU Affero General Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#include <set>
#include <string>
#include <utility>
#include <vector>
#include "mongo/base/owned_pointer_vector.h"
#include "mongo/db/storage/recovery_unit.h"
#include "mongo/platform/compiler.h"
#pragma once
namespace mongo {
/**
* Just pass through to getDur().
*/
class DurRecoveryUnit : public RecoveryUnit {
public:
DurRecoveryUnit();
virtual ~DurRecoveryUnit() { }
virtual void beginUnitOfWork(OperationContext* opCtx);
virtual void commitUnitOfWork();
virtual void endUnitOfWork();
virtual bool waitUntilDurable();
virtual void abandonSnapshot();
// The recovery unit takes ownership of change.
virtual void registerChange(Change* change);
virtual void* writingPtr(void* addr, size_t len);
virtual void setRollbackWritesDisabled();
virtual SnapshotId getSnapshotId() const { return SnapshotId(); }
private:
/**
* Marks writes for journaling, if enabled, and then commits all other Changes in order.
* Returns with empty _initialWrites, _mergedWrites, _changes and _preimageBuffer, but
* does not reset the _rollbackWritesDisabled or _mustRollback flags. This leaves the
* RecoveryUnit ready for more changes that may be committed or rolled back.
*/
void commitChanges();
/**
* Creates a list of write intents to be journaled, and hands it of to the active
* DurabilityInterface.
*/
void markWritesForJournaling();
/**
* Restores state by rolling back all writes using the saved pre-images, and then
* rolling back all other Changes in LIFO order. Resets internal state.
*/
void rollbackChanges();
bool inAUnitOfWork() const { return !_startOfUncommittedChangesForLevel.empty(); }
bool inOutermostUnitOfWork() const {
return _startOfUncommittedChangesForLevel.size() == 1;
}
/**
* If true, ending a unit of work will cause rollback. Ending a (possibly nested) unit of
* work without committing and without making any changes will not cause rollback.
*/
bool haveUncommittedChangesAtCurrentLevel() const {
return _writeCount > _startOfUncommittedChangesForLevel.back().writeCount
|| _changes.size() > _startOfUncommittedChangesForLevel.back().changeIndex;
}
/**
* Version of writingPtr that checks existing writes for overlap and only stores those
* changes not yet covered by an existing write intent and pre-image.
*/
void mergingWritingPtr(char* data, size_t len);
/**
* Reset to a clean state without any uncommitted changes or write.
*/
void resetChanges();
// Changes are ordered from oldest to newest.
typedef OwnedPointerVector<Change> Changes;
Changes _changes;
// Number of pending uncommitted writes. Incremented even if new write is fully covered by
// existing writes.
size_t _writeCount;
// Total size of the pending uncommitted writes.
size_t _writeBytes;
/**
* These are memory writes inside the mmapv1 mmap-ed files. A pointer past the end is just
* instead of a pointer to the beginning for the benefit of MergedWrites.
*/
struct Write {
Write(char* addr, int len, int offset) : addr(addr), len(len), offset(offset) { }
Write(const Write& rhs) : addr(rhs.addr), len(rhs.len), offset(rhs.offset) { }
Write() : addr(0), len(0), offset(0) { }
bool operator< (const Write& rhs) const { return addr < rhs.addr; }
struct compareEnd {
bool operator() (const Write& lhs, const Write& rhs) const {
return lhs.addr + lhs.len < rhs.addr + rhs.len;
}
};
char* end() const {
return addr + len;
}
char* addr;
int len;
int offset; // index into _preimageBuffer
};
/**
* Writes are ordered by ending address, so MergedWrites::upper_bound() can find the first
* overlapping write, if any. Overlapping and duplicate regions are forbidden, as rollback
* of MergedChanges undoes changes by address rather than LIFO order. In addition, empty
* regions are not allowed. Storing writes by age does not work well for large indexed
* arrays, as coalescing is needed to bound the size of the preimage buffer.
*/
typedef std::set<Write, Write::compareEnd> MergedWrites;
MergedWrites _mergedWrites;
// Generally it's more efficient to just store pre-images unconditionally and then
// sort/eliminate duplicates at commit time. However, this can lead to excessive memory
// use in cases involving large indexes arrays, where the same memory is written many
// times. To keep the speed for the general case and bound memory use, the first few MB of
// pre-images are stored unconditionally, but once the threshold has been exceeded, the
// remainder is stored in a more space-efficient datastructure.
typedef std::vector<Write> InitialWrites;
InitialWrites _initialWrites;
std::string _preimageBuffer;
// Index of the first uncommitted Change in _changes and number of writes for each nesting
// level. Store the number of writes as maintained in _writeCount rather than the sum of
// _initialWrites and _mergedWrites, as coalescing might otherwise result in
// haveUncommittedChangesAtCurrent level missing merged writes when determining if rollback
// is necessary. Index 0 in this vector is always the outermost transaction and back() is
// always the innermost. The size() is the current nesting level.
struct Indexes {
Indexes(size_t changeIndex, size_t writeCount)
: changeIndex(changeIndex)
, writeCount(writeCount)
{}
size_t changeIndex;
size_t writeCount;
};
std::vector<Indexes> _startOfUncommittedChangesForLevel;
// If true, this RU is in a "failed" state and all changes must be rolled back. Once the
// outermost WUOW rolls back it reverts to false.
bool _mustRollback;
// Default is false.
// If true, no preimages are tracked. If rollback is subsequently attempted, the process
// will abort.
bool _rollbackWritesDisabled;
};
} // namespace mongo
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