diff options
Diffstat (limited to 'src/mongo/s/metadata_loader.h')
| -rw-r--r-- | src/mongo/s/metadata_loader.h | 224 |
1 files changed, 111 insertions, 113 deletions
diff --git a/src/mongo/s/metadata_loader.h b/src/mongo/s/metadata_loader.h index 7d6e3d77798..15ca227926e 100644 --- a/src/mongo/s/metadata_loader.h +++ b/src/mongo/s/metadata_loader.h @@ -36,126 +36,124 @@ namespace mongo { - class CatalogManager; - class CollectionMetadata; - class CollectionType; - class DBClientCursor; +class CatalogManager; +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 DBLock lock while the pending chunk state *must* be. + * + * Example usage: + * beforeMetadata = <get latest local metadata>; + * remoteMetadata = makeCollectionMetadata( beforeMetadata, remoteMetadata ); + * DBLock lock(txn, dbname, MODE_X); + * 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: + explicit MetadataLoader(); + + ~MetadataLoader(); /** - * 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. + * 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. * - * 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(txn, dbname, MODE_X); - * afterMetadata = <get latest local metadata>; - * promotePendingChunks( afterMetadata, remoteMetadata ); + * Locking note: + * + Must not be called in a DBLock, since this loads over the network * - * 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.) + * OK on success. * - * The class is not thread safe. + * 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 */ - class MetadataLoader { - public: - - explicit MetadataLoader(); - - ~MetadataLoader(); + Status makeCollectionMetadata(CatalogManager* catalogManager, + const std::string& ns, + const std::string& shard, + const CollectionMetadata* oldMetadata, + CollectionMetadata* metadata) const; - /** - * 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(CatalogManager* catalogManager, - 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: + /** + * 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; - /** - * 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(CatalogManager* catalogManager, - const std::string& ns, - const std::string& shard, - CollectionMetadata* metadata) const; +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 + * + */ + Status _initCollection(CatalogManager* catalogManager, + 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(CatalogManager* catalogManager, - const std::string& ns, - const std::string& shard, - const CollectionMetadata* oldMetadata, - 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(CatalogManager* catalogManager, + const std::string& ns, + const std::string& shard, + const CollectionMetadata* oldMetadata, + CollectionMetadata* metadata) const; +}; -} // namespace mongo +} // namespace mongo |