This document covers the following topics:
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 can be any executable objects such as programs and dialogs. 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).
Resources are loaded into the buffer pool if they reside in a library of a Natural system file (for example, FUSER) and if their names do not exceed 32 characters (including the file extension).
Each resource that resides in the directory which is assigned to the
environment variable NATGUI_BMP or whose name is
longer than 32 characters, is loaded directly into the Natural process every
time it is accessed (that is: the resource is not loaded into the buffer
pool).
Depending on the individual requirements, it is possible to run different buffer pools of the same Natural version simultaneously on the same computer.
For each buffer pool, synchronization can be enabled in the Configuration Utility (see also Setting up a Buffer Pool below). All buffer pools which contain objects from the same system file and for which synchronization has been enabled are then synchronized automatically.
Important:
If the system file resides on a shared drive, synchronization
only works if the file system on the server is NTFS.
The following applies when synchronization has been enabled: If an object that is loaded to more than one buffer pool is modified by one Natural process, it is first marked as invalid. When the object is no longer used by any process, it is deleted from the buffer pool. The next time this object is requested by a process, it will be loaded into the buffer pool again.
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.
A read-only buffer pool is a special buffer pool that only allows read access. If an object is not found in the read-only buffer pool, Natural issues error 82 (object not found). As no attempt is made to retrieve the missing object in the system files, all lock operations on the system file as well as on the buffer pool are skipped. No account data are gathered. An unlimited number of users can access read-only buffer pool.
A read-only buffer pool is defined in the Configuration Utility (see also Setting up a Buffer Pool below). If a buffer pool has been defined as a read-only buffer pool, the value defined for the maximum number of users is ignored.
The utility NATBPSRV does not allocate
semaphores for a read-only buffer pool. It expects, however, a preload list in
a file named <bufferpool-name>.PRL at the location
of the Natural parameter files, which is defined in the local configuration
file (installation
assignments). For example, if the name of the read-only buffer pool
is "ROBP", the file name must be
ROBP.PRL.
A preload list can be generated using the Natural utility
CRTPRL. This
utility extracts the contents of a buffer pool and merges it with the existing
preload data of a buffer pool.
The preload list in the PRL file contains records with comma-separated data in the following form:
database-ID,file-number,library,object-name,kind,type
The keywords in the file have the same meaning as the keywords shown
by the DIR
command of the NATBPMON utility.
With the exception of directory-describing records (the kind of object
is D, which means the object is part of
FILEDIR.SAG), a value must be assigned to all keywords.
Examples:
| Keywords | NATBPSRV loads the following into
the buffer pool
|
|---|---|
222,111,MY_LIB,PGM1,G,P |
Object code of program PGM1 from
library MY_LIB which is located on database 222 and file number
111.
|
222,113,*,*,D |
LIBDIR.SAG which is
located on FNAT=222,113.
|
222,111,MY_LIB,*,D |
FILEDIR.SAG from library
MY_LIB which is located on FUSER=222,111 .
|
Using a read-only buffer pool has the disadvantage that the application must be known in detail (as missing objects cannot be loaded). This means that all objects needed by an application must be specified in the preload list. In seldom cases, the complete set of objects needed by an application can be determined in advance.
Natural can run with a read-only buffer pool as the primary buffer
pool. Such a buffer pool is not modifiable. Objects missing in the read-only
buffer pool cannot be loaded. If an object is not found in the read-only buffer
pool, Natural issues error 82 (object not found). To avoid this, Natural can
attach during execution to a secondary standard buffer pool (which allows
read/write access) and activate the missing objects there. If a call to locate
an object in the primary buffer pool fails, the secondary buffer pool operates
as a backup buffer pool. The dynamic parameter
BPID2
identifies the secondary buffer pool.
Other than for the read-only buffer pool, there is a maximum number of users that can attach to the secondary buffer pool and object locking through semaphores takes place each time the secondary buffer pool is accessed.
The preload list of the read-only buffer pool can be updated/enhanced
by merging the contents of the secondary read/write buffer pool with the
preload list of a read-only buffer pool using the utility
CRTPRL.
For a read-only buffer pool, it is possible to define the name of an alternate buffer pool in the Configuration Utility (see also Setting up a Buffer Pool below).
Using the SWAP command
of the NATBPMON utility, which is only available for a read-only
buffer pool, you can tag a read-only buffer pool as "obsolete".
All Natural sessions attached to an obsolete buffer pool will detach from this
buffer pool and will attach to the alternate buffer pool - but only if the
alternate buffer pool is also a read-only buffer pool. The swap from one buffer
pool to the other occurs either when Natural tries to load a new object (for
example, when executing a CALLNAT or RETURN
statement) or when Natural tries to interpret a command which has been put on
the stack. The IPC resources (that is, the shared memory segment) of a buffer
pool tagged as obsolete can be removed after issuing the
SWAP command of the NATBPMON utility.
This feature allows exchanging a buffer and its contents by another read-only
buffer pool with updated contents without stopping Natural sessions.
The Natural utility CRTPRL, which is located in the
library SYSBPM, is used to create a preload list for a read-only
buffer pool.
The utility uses the content of a source buffer pool as the basis for the preload list and checks whether the preload list already exists for a read-only (target) buffer pool:
If the preload list exists, the existing data in the preload list is merged with the data from the source buffer pool, and the preload list is saved with the new content.
If the preload list does not yet exist, it is created using the content from the source buffer pool.
The content of the resulting preload list determines the content of
the read-only buffer pool. The preload list is read by the utility
NATBPSRV which
loads the corresponding objects into the read-only buffer pool.
When using the Natural buffer pool, only minimum restrictions must be considered:
When a Natural session hangs up, do not terminate it by using the Windows Task Manager.
If this session is currently performing changes to the buffer pool internal data structures, an interruption may occur at a stage where the update is not fully completed. If the buffer pool internal data structures are inconsistent, this could have negative effects.
Note:
This can only happen when the Natural nucleus is executing buffer
pool routines.
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.
Natural uses a Windows service, the Software AG Natural n.n Buffer Pool Service, to start the Buffer Pool Server when the PC is booted.
Natural is installed with the default buffer pool NATBP.
NATBP is also used as the default buffer pool name at Natural
startup (a different buffer pool can be defined using the profile parameter
BPID).
You can modify the service configuration to meet your requirements. This is explained in the following topics:
The file natbpsvc.exe, which is stored in the Natural bin directory, is used to execute the service commands.
The following service commands can be specified in the Command Prompt window of Windows:
This example explains how to create a new buffer pool with the name
MYBP and how to start Natural with your new buffer pool.
To start Natural with your own buffer pool
Use the Configuration
Utility to define an additional buffer pool with the name
MYBP in the local configuration file. See
Buffer
Pool Assignments in the Configuration
Utility documentation.
Note:
For this example, you can use the same values as defined for the
default buffer pool NATBP.
Invoke the Command Prompt window of Windows.
Go to the Natural bin directory which contains the file natbpsvc.exe.
Enter the following command to create a buffer pool with the name
MYBP:
NATBPSVC CREATE MYBP
The following information is shown:
%NATBPSVC-I: Natural n.n Buffer Pool Service %NATBPSVC-I: New buffer pool 'MYBP' created %NATBPSVC-I: Natural n.n Buffer Pool Service
Important:
When the buffer pool with the specified name has not yet
been defined in the local configuration file, a corresponding message is shown
instead. Make sure to define the buffer pool in the local configuration file
before you proceed with the steps below.
Enter the following command to define that your buffer pool is to be started when the service is started:
NATBPSVC SET MYBP start=yes
The following information is shown:
%NATBPSVC-I: Natural n.n Buffer Pool Service %NATBPSVC-I: Configuration successfully set %NATBPSVC-I: Natural n.n Buffer Pool Service
Enter the following command to start your buffer pool now (without having to restart the service):
NATBPSVC START MYBP
The following information is shown:
%NATBPSVC-I: Natural n.n Buffer Pool Service %NATBPSVC-I: Send request to Natural n.n Buffer Pool Service %NATBPSVC-I: Buffer pool 'MYBP' started %NATBPSVC-I: Natural n.n Buffer Pool Service
Enter the following command to display the status of all buffer pools that are currently defined for the service:
NATBPSVC STATUS
The following information is shown:
%NATBPSVC-I: Natural n.n Buffer Pool Service
%NATBPSVC-I: Send request to Natural n.n Buffer Pool Service
%NATBPSVC-I: MYBP is active
NATBP is active
%NATBPSVC-I: Natural n.n Buffer Pool Service
Start Natural with the dynamic parameter
BPID as
shown below:
natural BPID=MYBP
The buffer pool is created using the utility NATBPSRV.
The buffer pool server is automatically started by the Natural Buffer Pool Service.
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.
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).
By default, the buffer pool NATBP is
started. If another buffer pool is
to be started, you specify its name with the following NATBPSRV
command line option:
NATBPSRV BP = buffer-pool-name
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. To ensure that modified objects are also removed from other buffer pools on the same computer to which the object is currenly loaded, you can enable the buffer pool synchronization in the Configuration Utility.
Natural provides two versions of the Buffer Pool Monitor: a
graphical user interface and the NATBPMON utility which is a
command line version.
For detailed information for how to use the different
versions of the Buffer Pool Monitor, see
Using the GUI Version of the Buffer
Pool Monitor and
Using the Command
Line Version of the Buffer Pool Monitor
(NATBPMON).
This section describes problems that may occur when using the Natural buffer pool and how to solve them.
The following is a typical command output example, with an explanation of what went wrong during execution.
Either Natural or the Natural Buffer Pool Monitor cannot be started.
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 NATBPMON utility, and the
buffer pool is not active.
You try to start Natural and the following message appears:
Natural Startup Error 16: Unable to open buffer pool. Buffer pool error: "unexpected system call error occurred" (20) Buffer pool could not attach to the global shared memory.
You try to start the Natural Buffer Pool Monitor and the following message appears:
Cannot get shared memory Buffer pool error: "unexpected system call error occurred" (20) Buffer pool could not attach to the global shared memory.
Start the buffer pool service as described in Using the Natural Buffer Pool Service.
When Natural or Natural Runtime is installed on a file server, a service called Software AG Natural n.n Client Buffer Pool Service is installed in the client environment (natcbpsvc.exe). This service is only installed during a client installation. It is used to create the shared memory for the Natural buffer pool server.
In the client environment, the Natural buffer pool server is started by a Natural process. This is different from a local installation on a PC where the Natural buffer pool server is started by the Natural buffer pool service.
The client buffer pool service cannot be configured using service commands.