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/**
* Copyright (C) 2012 10gen 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.
*/
#pragma once
#include <string>
#include "mongo/base/status.h"
#include "mongo/client/dbclientinterface.h"
#include "mongo/db/jsobj.h"
namespace mongo {
class CollectionMetadata;
class CollectionType;
class DBClientCursor;
/**
* The MetadataLoader is responsible for interfacing with the config servers and previous
* metadata to build new instances of CollectionMetadata. MetadataLoader is the "builder"
* class for metadata.
*
* CollectionMetadata has both persisted and volatile state (for now) - the persisted
* config server chunk state and the volatile pending state which is only tracked locally
* while a server is the primary. This requires a two-step loading process - the persisted
* chunk state *cannot* be loaded in a DBWrite lock while the pending chunk state *must* be.
*
* Example usage:
* beforeMetadata = <get latest local metadata>;
* remoteMetadata = makeCollectionMetadata( beforeMetadata, remoteMetadata );
* DBWrite lock( ns );
* afterMetadata = <get latest local metadata>;
* promotePendingChunks( afterMetadata, remoteMetadata );
*
* The loader will go out of its way to try to fetch the smaller amount possible of data
* from the config server without sacrificing the freshness and accuracy of the metadata it
* builds. (See ConfigDiffTracker class.)
*
* The class is not thread safe.
*/
class MetadataLoader {
public:
/**
* Takes a connection std::string to the config servers to be used for loading data. Note
* that we make no restrictions about which connection std::string that is, including
* CUSTOM, which we rely on in testing.
*/
explicit MetadataLoader( const ConnectionString& configLoc );
~MetadataLoader();
/**
* Fills a new metadata instance representing the chunkset of the collection 'ns'
* (or its entirety, if not sharded) that lives on 'shard' with data from the config server.
* Optionally, uses an 'oldMetadata' for the same 'ns'/'shard'; the contents of
* 'oldMetadata' can help reducing the amount of data read from the config servers.
*
* Locking note:
* + Must not be called in a DBLock, since this loads over the network
*
* OK on success.
*
* Failure return values:
* Abnormal:
* @return FailedToParse if there was an error parsing the remote config data
* Normal:
* @return NamespaceNotFound if the collection no longer exists
* @return HostUnreachable if there was an error contacting the config servers
* @return RemoteChangeDetected if the data loaded was modified by another operation
*/
Status makeCollectionMetadata( const std::string& ns,
const std::string& shard,
const CollectionMetadata* oldMetadata,
CollectionMetadata* metadata ) const;
/**
* Replaces the pending chunks of the remote metadata with the more up-to-date pending
* chunks of the 'after' metadata (metadata from after the remote load), and removes pending
* chunks which are now regular chunks.
*
* Pending chunks should always correspond to one or zero chunks in the remoteMetadata
* if the epochs are the same and the remote version is the same or higher, otherwise they
* are not applicable.
*
* Locking note:
* + Must be called in a DBLock, to ensure validity of afterMetadata
*
* Returns OK if pending chunks correctly follow the rule above or are not applicable
* Returns RemoteChangeDetected if pending chunks do not follow the rule above, indicating
* either the config server or us has changed unexpectedly.
* This should only occur with manual editing of the config
* server.
*
* TODO: This is a bit ugly but necessary for now. If/when pending chunk info is stored on
* the config server, this should go away.
*/
Status promotePendingChunks( const CollectionMetadata* afterMetadata,
CollectionMetadata* remoteMetadata ) const;
private:
ConnectionString _configLoc;
/**
* Returns OK and fills in the internal state of 'metadata' with general collection
* information, not including chunks.
*
* If information about the collection can be accessed or is invalid, returns:
* @return NamespaceNotFound if the collection no longer exists
* @return FailedToParse if there was an error parsing the remote config data
* @return HostUnreachable if there was an error contacting the config servers
* @return RemoteChangeDetected if the collection doc loaded is unexpectedly different
*
*/
Status initCollection( const std::string& ns,
const std::string& shard,
CollectionMetadata* metadata ) const;
/**
* Returns OK and fills in the chunk state of 'metadata' to portray the chunks of the
* collection 'ns' that sit in 'shard'. If provided, uses the contents of 'oldMetadata'
* as a base (see description in initCollection above).
*
* If information about the chunks can be accessed or is invalid, returns:
* @return HostUnreachable if there was an error contacting the config servers
* @return RemoteChangeDetected if the chunks loaded are unexpectedly different
*
* For backwards compatibility,
* @return NamespaceNotFound if there are no chunks loaded and an epoch change is detected
* TODO: @return FailedToParse
*/
Status initChunks( const std::string& ns,
const std::string& shard,
const CollectionMetadata* oldMetadata,
CollectionMetadata* metadata ) const;
};
} // namespace mongo
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