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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 <vector>
#include "mongo/base/status.h"
namespace mongo {
class ShardingCatalogClient;
class ChunkType;
class CollectionMetadata;
class CollectionType;
class NamespaceString;
class OID;
class OperationContext;
/**
* 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 DBLock lock while the pending chunk state *must* be.
*
* Example usage:
* beforeMetadata = <get latest local metadata>;
* remoteMetadata = makeCollectionMetadata( beforeMetadata, remoteMetadata );
* DBLock lock(opCtx, dbname, MODE_X);
* afterMetadata = <get latest local metadata>;
*
* 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.)
*
*/
class MetadataLoader {
public:
/**
* 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
*/
static Status makeCollectionMetadata(OperationContext* opCtx,
ShardingCatalogClient* catalogClient,
const std::string& ns,
const std::string& shard,
const CollectionMetadata* oldMetadata,
CollectionMetadata* metadata);
private:
/**
* 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
*
*/
static Status _initCollection(OperationContext* opCtx,
ShardingCatalogClient* catalogClient,
const std::string& ns,
const std::string& shard,
CollectionMetadata* metadata);
/**
* 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
*/
static Status _initChunks(OperationContext* opCtx,
ShardingCatalogClient* catalogClient,
const std::string& ns,
const std::string& shard,
const CollectionMetadata* oldMetadata,
CollectionMetadata* metadata);
/**
* Takes a vector of 'chunks' and updates the config.chunks.ns collection specified by 'nss'.
* Any chunk documents in config.chunks.ns that overlap with a chunk in 'chunks' is removed
* as the new chunk document is inserted. If the epoch of any chunk in 'chunks' does not match
* 'currEpoch', the chunk metadata is dropped.
*
* @nss - the regular collection namespace for which chunk metadata is being updated.
* @chunks - a range of chunks retrieved from the config server, sorted in ascending chunk
* version order.
* @currEpoch - what this shard server knows to be the collection epoch.
*
* Returns:
* - OK if not primary and no writes are needed.
* - RemoteChangeDetected if the chunk version epoch of any chunk in 'chunks' is different than
* 'currEpoch'
* - Other errors in writes/reads to the config.chunks.ns collection fails.
*/
static Status _writeNewChunksIfPrimary(OperationContext* opCtx,
const NamespaceString& nss,
const std::vector<ChunkType>& chunks,
const OID& currEpoch);
};
} // namespace mongo
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