FRS Tables

FRS transactions are stored in a Microsoft Jet database that defaults to systemroot\\Ntfrs\Jet\Ntfrs.jdb. Each replica set hosted by a computer has a set of tables stored in the Ntfrs.jdb file. These five tables are:

• Connection table. Contains one record per link or inbound/outbound partner connection.
• Inbound log. Stores pending change orders to be processed. As entries are processed, acknowledgments are sent to the inbound partners. Data stored in the inbound log includes change order globally unique identifier (GUID), file name, object ID, parent object ID, version number, and event time.

  During a planned shutdown, all new change orders since the last update are written to the inbound log. If an unplanned shutdown or network interruption occurs, the inbound partner resends all the change orders in its outbound log for which acknowledgments have not been received.

• Outbound log. Stores pending change orders to be sent to outbound partners. Change orders remain in the outbound log until all outbound partners receive and acknowledge the change. Data stored in the outbound log is the same as that stored in the inbound log. Also in the outbound log is the leading (next change) and trailing (last acknowledged) index for each partner.

  The outbound log or logs can become quite large, particularly when replicas are down, links between replicas are slow, replication hours are restricted, or a large number of changes occur. For example, suppose one of four replicas is down. Snapshots of the file image and log entries are maintained until this server becomes available. When the changes are finally sent, the inbound partner sends all changes in log file order.

  If the trailing location for a replica partner is overwritten, a complete synchronization must be completed for the replica. This involves the outbound partner sending its version vector — an array of numbers for each originator — with the changes it has received to the inbound partner. The inbound partner checks its ID table by using this state to determine what changes occurred afterward and sends them.

• Version vector. Measures the up-to-dateness of a replica compared to another replica. Each replica member in a replica set is assigned a number. Version vector joins occur the first time an FRS context is replicated or when the outbound log wraps.
• ID table. Lists all files in the replica set of which FRS is aware. Data stored in the ID table includes globally unique identifier (GUID), file name ID, parent file ID, file object ID, parent object ID, version number, and event time.

Changes are always logged in the Jet database for recovery purposes before any disk files are moved in case of a system failure.

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