Browse Prior Art Database

Coordinated Method of Closing All File Handles Opened by Multiple Database Agent Processes

IP.com Disclosure Number: IPCOM000109748D
Original Publication Date: 1992-Sep-01
Included in the Prior Art Database: 2005-Mar-24
Document File: 2 page(s) / 112K

Publishing Venue

IBM

Related People

Buquoi, GH: AUTHOR [+5]

Abstract

Disclosed is an algorithm to ensure that all database agent processes close the file handles they have open for a particular database. In the Database Manager Distributed Database System version 2.0 (DBM 2.0), many DBM Agent processes may eventually open file handles for one particular file. When the processing for this database file has been completed, all file handles in the system must be closed in a coordinated fashion.

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This is the abbreviated version, containing approximately 52% of the total text.

Coordinated Method of Closing All File Handles Opened by Multiple Database Agent Processes

       Disclosed is an algorithm to ensure that all database
agent processes close the file handles they have open for a
particular database.  In the Database Manager Distributed Database
System version 2.0 (DBM 2.0), many DBM Agent processes may eventually
open file handles for one particular file.  When the processing for
this database file has been completed, all file handles in the system
must be closed in a coordinated fashion.

      In the DBM 2.0 system, there is a set of Database Agent
processes which service the database requests on behalf of the
application programs.  Each DBM Agent process may service requests
from any of the applications at any time.  It is possible for all of
the Agents to eventually open file handles for a particular database
during the execution of an application which accesses this database.

      These file handles must be closed when processing of the
database has completed.  Closing all the file handles is required
because operations, such as dropping the database, are blocked if any
file handles remain open in the system.  All file handles must be
closed before a table can be divided for media spanning, also.  A
mechanism must be defined to ensure that the file handles for a
particular file are closed by each DBM Agent process in a coordinated
fashion.

      The file handle closing coordination scheme invented for DBM
2.0 employs interprocess communications using message queues, signals
and semaphores.  The coordination starts in the Agent process which
services the last disconnection request from an application for a
specific database.  This Agent process queues a message to the
central DBM System Monitor which is a process specifically designed
to monitor and control the rest of the DBM Agent processes.  The
message sent to the System Monitor contains a token to identify the
specific database to be closed, a token to identify the file(s) whose
handle(s) are to be closed, and a pointer to the control block
representing the Agent process originating the file handle cleanup.
The originating Agent process then waits on a semaphore to be cleared
by the System Monitor when all other Agent processes have completed
cleaning up the specified file handles.

      The DBM System Monitor maintains a linked list of the DBM Agent
processes.  When the System Monitor receives the file closing
request, it traverses the linked list and places the database token
and file token in the control block for each DBM Agent.  The System
Monitor also sends a special user-defined "close file" signal to each
DBM Agent process.  A count of all the Agents signalled is set and
the System...