Importance

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Abstract

A client-server computer system has one or more clients connected to one or more servers. During request/reply interactions, a client-side application sends a request for services (e.g., read a file, return some information, update a database record, process data, etc.) to the server. A server-side application request program processes the request, prepares a reply to the request, and returns the reply to the client-side application. The server runs a resource manager to log operations and data pages in a manner that enables application and database recovery. Among other tasks, the server's resource manager creates a stable log file that can be used to help recover the client-side application in the event of a system crash. To capture the client-server interaction, the server's resource manager records the reply in the log buffer and commits the reply record to the stable log before the reply is sent back to the client. This results in only one forced logging event for each request/reply exchange. The server further maintains an active application table and a message lookup table to speed recovery. The active application table lists all currently active applications running at the client and server to identify those applications that should be recovered. The message lookup table keeps copies of the logged replies that can be used during client recovery in place of the logged records to avoid searching the server's stable log file. The server further truncates parts of its stable log file when notified that reply log records are no longer needed by the client.

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First Claim