Version 6.3.8 for OpenVMS
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Natural Buffer Pool

This document covers the following topics:


General Information

The Natural buffer pool is used to share Natural objects between several Natural processes that access objects on the same computer. It is a storage area into which compiled Natural programs are placed in preparation for their execution. Programs are moved into and out of the buffer pool as Natural users request Natural objects.

Since Natural generates reentrant Natural object code, it is possible that a single copy of a Natural program can be executed by more than one user at the same time. For this purpose, each object is loaded only once from the system file into the Natural buffer pool, instead of being loaded by every caller of the object.

The following topics are covered below:

Objects in the Buffer Pool

Objects in the buffer pool can be any executable objects such as programs and maps. The following executable objects are only placed in the buffer pool for compilation purposes: local data areas, parameter data areas and copycodes.

When a Natural object is loaded into the buffer pool, a control block called a directory entry is allocated for that object. This control block contains information such as the name of the object, to which library or application the object belongs, from which database ID and Natural system file number the object was retrieved, and certain statistical information (for example, the number of users who are concurrently executing a program).

Coordination under OpenVMS

The buffer pool uses a standard locking mechanism which need not be configured by the administrator.

Multiple Buffer Pools

Depending on the individual requirements, it is possible to run different buffer pools of the same Natural version simultaneously on the same computer.

Storing Objects in the Buffer Pool

When a user executes a program, a call is made to the buffer pool manager. The directory entries are searched to determine whether the program has already been loaded into the buffer pool. If it does not yet exist in the buffer pool, a copy is retrieved from the appropriate library and loaded into the buffer pool.

When a Natural object is being loaded into the buffer pool, a new directory entry is defined to identify this program, and one or more other Natural objects which are currently not being executed may be deleted from the buffer pool in order to make room for the newly loaded object.

For this purpose, the buffer pool maintains a record of which user is currently using which object, and it detects situations in which a user exits Natural without releasing all its objects. It dynamically deletes unused or out-of-date objects to accommodate new objects belonging to other applications.

Restrictions

When using the Natural buffer pool, only minimum restrictions must be considered:

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Setting up a Buffer Pool

The buffer pool assignments are stored in the local configuration file. To set up a buffer pool, you have to specify specific values in the local configuration file using the Configuration Utility. For a list of these values, see Buffer Pool Assignments in the Configuration Utility documentation.

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Using the Utility NATBPSRV for Creating the Buffer Pool

The buffer pool is created using the utility NATBPSRV.

Note:
The utility NATBPSRV should not be accessible to all Natural users, because it can cause damage to the work of other buffer pool users.

The following system privileges are required: CMKRNL, PRMGBL, SYSGBL, SYSNAM, SYSPRV.

NATBPSRV allocates the resources required by the buffer pool and creates the permanent communication facilities (that is, shared memory and semaphores) used for the buffer pool. The necessary specifications for the resources and facilities are made with the Configuration Utility (see Setting up a Buffer Pool).

The NATBPSRV utility should only be used during system startup, from within the startup procedure STARTUP_NAT<v>.COM (where <v> in the file name stands for the first digit of the Natural version number).

NATBPSRV without a parameter starts the buffer pool NATBP. If another buffer pool is to be started, you specify its name with the following NATBPSRV command line option:

NATBPSRV BP = buffer-pool-name

If NATBPSRV discovers in the process of creating a buffer pool that a buffer pool of the same name is already active, it deletes the already active buffer pool. If the deletion fails, NATBPSRV terminates with an appropriate error message.

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Monitoring the Buffer Pool

The Buffer Pool Monitor is used to oversee the buffer pool's activity during its operation. The Buffer Pool Monitor can also be used to shut down the buffer pool when Natural must be stopped on a computer.

The Buffer Pool Monitor collects information on the current state of your Natural buffer pool.

If multiple buffer pools are active on the same computer and an object that is loaded to more than one buffer pool is modified by a Natural process, the object will only be removed from the buffer pool to which the modifying Natural process is attached.

For detailed information for how to use the Buffer Pool Monitor, see Using the Buffer Pool Monitor (NATBPMON).

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Trouble Shooting

This section describes problems that may occur when using the Natural buffer pool and how to solve them.

The following are typical command output examples, with an explanation of what went wrong during execution.

Problem

Either Natural or the Natural Buffer Pool Monitor (NATBPMON utility) cannot be started.

Examples

The following examples describe the most typical problems you are likely to encounter as a Natural administrator or user. These problems occur when you start Natural or the Natural Buffer Pool Monitor, and the buffer pool is not active.

You try to start Natural with the following command:

NATnnURAL

The following message appears:

Unable to open Buffer Pool, 
Buffer Pool error: "unexpected system call error occurred" (20) 
Global shared memory could not be attached.: NATBP6340_NODE1

%SYSTEM-W-NOSUCHSEC, no such (global) section

You try to start the Natural Buffer Pool Monitor with the following command:

NATnnBPMON

When you enter the STATUS command at the NATBPMON prompt, the following message appears:

%SYSTEM-W-NOSUCHSEC, no such (global) section 
Buffer Pool error: "unexpected system call error occurred" (20)
Global shared memory could not be attached.: NATBP6340_NODE1

Solution

Start the buffer pool service from a sufficiently privileged account as shown in the following example:

$ @STARTUP_NAT<v>.COM STARTUP BP

where <v> in the file name stands for the first digit of the Natural version number.

This command procedure is either located in SYS$STARTUP or in the directory SAG$ROOT:[NATURAL].

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Shutting Down and Restarting the Buffer Pool

Usually it should not be necessary to shut down and restart the buffer pool. This may only be necessary if the buffer pool should become unusable due to serious internal errors in the buffer pool, which is extremely unlikely to occur, or because the parameters defining the buffer pool structure became obsolete.

If the NATBPMON utility is still able to access the buffer pool, proceed as follows:

  1. Shut down the buffer pool with the SHUTDOWN command of the NATBPMON utility.

    Once the SHUTDOWN command is executed, new users are denied access to the buffer pool.

    Tip:
    Active buffer pool users can be monitored by issuing the WHO and STATUS commands of the NATBPMON utility.

  2. After the last user has stopped accessing the buffer pool, buffer pool resources can be deleted by issuing the IPCRM command of the NATBPMON utility.

  3. To restart the buffer pool, call the file STARTUP_NAT<v>.COM from a sufficiently privileged account (where <v> in the file name stands for the first digit of the Natural version number).

You can use the FORCE option of the SHUTDOWN command:

  1. Shut down the buffer pool with the SHUTDOWN FORCE grace-period command of the NATBPMON utility.

    This command - like the SHUTDOWN command without options - denies new users access the buffer pool. However, the terminate signal SIGTERM is sent to all active Natural sessions, forcing them to log off from the buffer pool.

    If the optional parameter grace-period is omitted, this command waits until all active sessions have performed their shutdown processing and then executes the IPCRM command of the NATBPMON utility .

    If the optional parameter grace-period has been specified, NATBPMON waits the specified number of seconds before it executes its IPCRM command - regardless of the closedown status of the sessions logged on to the buffer pool. Therefore, the value defined for the grace period should be sufficiently large to allow the sessions to terminate in time.

    Note:
    SHUTDOWN FORCE 0 is the same as SHUTDOWN FORCE (without the parameter grace-period).

  2. To restart the buffer pool after successful execution of the SHUTDOWN FORCE command, call the file STARTUP_NAT<v>.COM from a sufficiently privileged account (where <v> in the file name stands for the first digit of the Natural version number).

If the NATBPMON utility is not able to perform a clean shutdown of the buffer pool, the buffer pool must be deleted by using operating system commands. It is only possible to rename the section file, because a section file cannot be deleted as long as it is locked by another user. Then restart the buffer pool using STARTUP_NAT<v>.COM and delete the renamed section file after the next reboot.

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