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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 <list>
#include "mongo/db/logical_time.h"
#include "mongo/db/namespace_string.h"
#include "mongo/db/s/scoped_collection_metadata.h"
#include "mongo/s/catalog/type_chunk.h"
#include "mongo/util/concurrency/with_lock.h"
namespace mongo {
class RangePreserver;
/**
* Contains filtering metadata for a sharded collection.
*/
class MetadataManager : public std::enable_shared_from_this<MetadataManager> {
public:
MetadataManager(ServiceContext* serviceContext,
NamespaceString nss,
CollectionMetadata initialMetadata);
~MetadataManager() = default;
MetadataManager(const MetadataManager&) = delete;
MetadataManager& operator=(const MetadataManager&) = delete;
/**
* Increments the usage counter of the active metadata and returns an RAII object, which
* corresponds to it.
*
* Holding a reference on a particular instance of the metadata means that orphan cleanup is not
* allowed to run and delete chunks which are covered by that metadata. When the returned
* ScopedCollectionDescription goes out of scope, the reference counter on the metadata will be
* decremented and if it reaches to zero, orphan cleanup may proceed.
*/
std::shared_ptr<ScopedCollectionDescription::Impl> getActiveMetadata(
const boost::optional<LogicalTime>& atClusterTime);
/**
* Returns the placement version of the active metadata object.
*/
ChunkVersion getActivePlacementVersion() {
stdx::lock_guard<Latch> lg(_managerLock);
invariant(!_metadata.empty());
return _metadata.back()->metadata->getShardPlacementVersion();
}
/**
* Returns the UUID of the collection tracked by this MetadataManager object.
*/
UUID getCollectionUuid() const {
return _collectionUuid;
}
/**
* Returns the number of CollectionMetadata objects being maintained on behalf of running
* queries. The actual number may vary after it returns, so this is really only useful for unit
* tests.
*/
size_t numberOfMetadataSnapshots() const;
/**
* Returns the number of metadata objects that have been set to boost::none in
* _retireExpiredMetadata(). The actual number may vary after it returns, so this is really only
* useful for unit tests.
*/
int numberOfEmptyMetadataSnapshots() const;
void setFilteringMetadata(CollectionMetadata newMetadata);
/**
* Returns a future marked as ready when all the ongoing queries retaining the range complete
*/
SharedSemiFuture<void> getOngoingQueriesCompletionFuture(ChunkRange const& range);
private:
// Management of the _metadata list is implemented in RangePreserver
friend class RangePreserver;
/**
* Represents an instance of what the filtering metadata for this collection was at a particular
* point in time along with a counter of how many queries are still using it.
*/
struct CollectionMetadataTracker {
CollectionMetadataTracker(const CollectionMetadataTracker&) = delete;
CollectionMetadataTracker& operator=(const CollectionMetadataTracker&) = delete;
CollectionMetadataTracker(CollectionMetadata inMetadata)
: metadata(std::move(inMetadata)) {}
~CollectionMetadataTracker() {
invariant(!usageCounter);
onDestructionPromise.emplaceValue();
}
boost::optional<CollectionMetadata> metadata;
/**
* Promise that will be signaled when this object is destroyed.
*
* In the case where this CollectionMetadataTracker may refer to orphaned documents for one
* or more ranges, the corresponding futures from this promise are used as barriers to
* prevent range deletion tasks for those ranges from proceeding until this object is
* destroyed, to guarantee that ranges aren't deleted while active queries can still access
* them.
*/
SharedPromise<void> onDestructionPromise;
uint32_t usageCounter{0};
};
/**
* Retires any metadata that has fallen out of use, potentially allowing range deletions to
* proceed which were waiting for active queries using these metadata objects to complete.
*/
void _retireExpiredMetadata(WithLock);
/**
* Pushes current set of chunks, if any, to _metadataInUse, replaces it with newMetadata.
*/
void _setActiveMetadata(WithLock wl, CollectionMetadata newMetadata);
/**
* Finds the most-recently pushed metadata that depends on `range`, or nullptr if none. The
* result is usable until the lock is released.
*/
CollectionMetadataTracker* _findNewestOverlappingMetadata(WithLock, ChunkRange const& range);
// ServiceContext from which to obtain instances of global support objects
ServiceContext* const _serviceContext;
// Namespace for which this manager object applies
const NamespaceString _nss;
// The UUID for the collection tracked by this manager object.
const UUID _collectionUuid;
// Mutex to protect the state below
mutable Mutex _managerLock = MONGO_MAKE_LATCH("MetadataManager::_managerLock");
// Contains a list of collection metadata for the same collection uuid, ordered in
// chronological order based on the refreshes that occurred. The entry at _metadata.back() is
// the most recent metadata and is what is returned to new queries. The rest are previously
// active collection metadata instances still in use by active server operations or cursors.
std::list<std::shared_ptr<CollectionMetadataTracker>> _metadata;
};
} // namespace mongo
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