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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* 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
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* 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 Server Side 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.
*/
#pragma once
#include <boost/optional.hpp>
#include <cstddef>
#include <vector>
#include "mongo/base/counter.h"
#include "mongo/bson/bsonobj.h"
#include "mongo/util/time_support.h"
namespace mongo {
class OperationContext;
namespace repl {
/**
* Interface for temporary container of oplog entries (in BSON format) from sync source by
* OplogFetcher that will be read by applier in the InitialSyncer.
*
* Implementations are only required to support one pusher and one popper.
*/
class OplogBuffer {
OplogBuffer(const OplogBuffer&) = delete;
OplogBuffer& operator=(const OplogBuffer&) = delete;
public:
/**
* Type of item held in the oplog buffer;
*/
using Value = BSONObj;
/**
* Batch of oplog entries (in BSON format) for bulk read/write operations.
*/
using Batch = std::vector<Value>;
/**
* Counters for this oplog buffer.
*/
class Counters;
OplogBuffer() = default;
virtual ~OplogBuffer() = default;
/**
* Causes the oplog buffer to initialize its internal state (start threads if appropriate,
* create backing storage, etc). This method may be called at most once for the lifetime of an
* oplog buffer.
*/
virtual void startup(OperationContext* opCtx) = 0;
/**
* Signals to the oplog buffer that it should shut down. This method may block. After
* calling shutdown, it is illegal to perform read/write operations on this oplog buffer.
*
* It is legal to call this method multiple times, but it should only be called after startup
* has been called.
*/
virtual void shutdown(OperationContext* opCtx) = 0;
/**
* Pushes operations in the iterator range [begin, end) into the oplog buffer without blocking.
*/
virtual void push(OperationContext* opCtx,
Batch::const_iterator begin,
Batch::const_iterator end) = 0;
/**
* Returns when enough space is available.
*/
virtual void waitForSpace(OperationContext* opCtx, std::size_t size) = 0;
/**
* Returns true if oplog buffer is empty.
*/
virtual bool isEmpty() const = 0;
/**
* Maximum size of all oplog entries that can be stored in this oplog buffer as measured by the
* BSONObj::objsize() function.
*
* Returns 0 if this oplog buffer has no size constraints.
*/
virtual std::size_t getMaxSize() const = 0;
/**
* Total size of all oplog entries in this oplog buffer as measured by the BSONObj::objsize()
* function.
*/
virtual std::size_t getSize() const = 0;
/**
* Returns the number/count of items in the oplog buffer.
*/
virtual std::size_t getCount() const = 0;
/**
* Clears oplog buffer.
*/
virtual void clear(OperationContext* opCtx) = 0;
/**
* Returns false if oplog buffer is empty. "value" is left unchanged.
* Otherwise, removes last item (saves in "value") from the oplog buffer and returns true.
*/
virtual bool tryPop(OperationContext* opCtx, Value* value) = 0;
/**
* Waits "waitDuration" for an operation to be pushed into the oplog buffer.
* Returns false if oplog buffer is still empty after "waitDuration".
* Otherwise, returns true.
*/
virtual bool waitForData(Seconds waitDuration) = 0;
/**
* Returns false if oplog buffer is empty.
* Otherwise, returns true and sets "value" to last item in oplog buffer.
*/
virtual bool peek(OperationContext* opCtx, Value* value) = 0;
/**
* Returns the item most recently added to the oplog buffer or nothing if the buffer is empty.
*/
virtual boost::optional<Value> lastObjectPushed(OperationContext* opCtx) const = 0;
/**
* Enters "drain mode". May only be called by the producer. When the buffer is in drain mode,
* "waitForData" will return immediately even if there is data in the queue. This
* is an optimization and subclasses may choose not to implement this function.
*/
virtual void enterDrainMode(){};
/**
* Leaves "drain mode". May only be called by the producer.
*/
virtual void exitDrainMode(){};
};
class OplogBuffer::Counters {
public:
/**
* Sets maximum size of operations for this OplogBuffer.
* This function should only be called by a single thread.
*/
void setMaxSize(std::size_t newMaxSize) {
maxSize.increment(newMaxSize - maxSize.get());
}
/**
* Clears counters.
* This function should only be called by a single thread.
*/
void clear() {
count.decrement(count.get());
size.decrement(size.get());
}
void increment(const Value& value) {
count.increment(1);
size.increment(std::size_t(value.objsize()));
}
void decrement(const Value& value) {
count.decrement(1);
size.decrement(std::size_t(value.objsize()));
}
// Number of operations in this OplogBuffer.
Counter64 count;
// Total size of operations in this OplogBuffer. Measured in bytes.
Counter64 size;
// Maximum size of operations in this OplogBuffer. Measured in bytes.
Counter64 maxSize;
};
/**
* An OplogBuffer interface which also supports random access by timestamp.
* The entries in a RandomAccessOplogBuffer must be pushed in strict timestamp order.
*
* The user of a RandomAccesOplogBuffer may seek to or find timestamps which have already been read
* from the buffer. It is up to the implementing subclass to ensure that such timestamps are
* available to be read.
*/
class RandomAccessOplogBuffer : public OplogBuffer {
public:
enum SeekStrategy {
kInexact = 0,
kExact = 1,
};
/**
* Retrieves an oplog entry by timestamp. Returns ErrorCodes::NoSuchKey if no such entry is
* found. Does not change current position of oplog buffer.
*/
virtual StatusWith<Value> findByTimestamp(OperationContext* opCtx, const Timestamp& ts) = 0;
/**
* Change current position of oplog buffer to point to the entry with timestamp 'ts'. If
* 'exact' is true, return NoSuchKey if the timestamp is not found. Otherwise, position will
* be before the next timestamp greater than or equal to 'ts'.
*/
virtual Status seekToTimestamp(OperationContext* opCtx,
const Timestamp& ts,
SeekStrategy exact = SeekStrategy::kExact) = 0;
};
} // namespace repl
} // namespace mongo
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