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 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).
Resource sharing requires that access to the buffer pool be coordinated among all users. Several system resources are necessary to accomplish this. For example, shared memory on the UNIX operating system is used to store the objects and their administrative information. To synchronize access to these objects, a set of semaphores is used. The amount of available shared memory and the number of semaphores is configured statically in the operating system, and as a result, it may be necessary to change system parameters and to recreate the operating system kernel for your installation. Further information about these topics is system-dependent and is described in the installation documentation for your UNIX computer.
Depending on the individual requirements, it is possible to run different buffer pools of the same Natural version simultaneously on the same computer.
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 values defined for the maximum number of users and for the semaphore key are 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.
Known issues: The IPCRM command of the
NATBPMON utility will report an error trying to delete the
semaphores associated to a read-only buffer pool.
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
UNIX command
kill -KILL (also kill
-9), the terminal command break or the
interrupt key.
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.
Instead, use the UNIX command kill
-TERM (also kill -15) to terminate the
hung-up session.
Note:
This can only happen when the Natural nucleus is executing buffer
pool routines.
All resources must be shared among all users of one Natural buffer pool. Group membership of a process is used to give access rights for the buffer pool. This means that the shared memory can be changed by all group members, but not by anyone else. The same applies to the semaphores.
Note:
All users of the same Natural buffer pool must belong to
the same user group on the UNIX operating system.
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.
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.
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 natstart.bsh.
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
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.
NATBPSRV can issue the following error messages if the
buffer pool that is to be created is meant to be a read-only buffer pool:
| Unable to attach to buffer pool. Return code ... received from bp_init. | |
| Explanation |
To load the objects described in the preload list,
|
| Action |
Contact Software AG Technical Support. |
| Unable to get parameter path. | |
| Explanation |
The path defined in the local configuration file identifying Natural's parameter files could not be established. |
| Action |
Contact Software AG Technical Support. |
| File ... is not accessible. | |
| Explanation |
The preload list is not accessible or not present. |
| Action |
Revise access rights or create a preload list. |
| Unable to open file ... | |
| Explanation |
The preload list cannot be read. |
| Action |
Re-create preload list. |
| Skipped erroneous record: '...'. Buffer pool may not operate correctly. | |
| Explanation |
An invalid record was found in the preload list. The record is skipped and the load process is continued. There may arise errors in your application due to missing objects. |
| Action |
Correct the record if it has been created manually, or contact Software AG Technical Support. |
| Unable to retrieve LIBDIR.SAG in FNAT(...,...). Application will not run. | |
| Explanation |
LIBDIR.SAG was not found. An application
depending on |
| Action |
Correct the record if it has been created manually, or contact Software AG Technical Support. |
| Buffer pool manager returned with error code ... . Buffer pool is not operational. | |
| Explanation |
FILEDIR.SAG could not be loaded into the buffer pool. The buffer pool is either too small to hold FILEDIR.SAG or FILEDIR.SAG is damaged. The previously listed message tells which FILEDIR.SAG is causing the trouble. |
| Action |
Correct the record if it has been created manually, or contact Software AG Technical Support. |
| Buffer pool manager returned with error code ... . Error ... occurred. | |
| Explanation |
An error occurred loading an object into the buffer pool. |
| Action |
Normally, the size of the buffer pool is too small. Increase its size and repeat the operation. If the problem remains, contact Software AG Technical Support. |
| Object ... in library ... on system file (...,...) not found. Application may not run. | |
| Explanation |
The preload record processed pointed to an object that was not found. This normally happens if an application is modified and the corresponding preload list is not updated. |
| Action |
Remove/revise preload record in question |
| Preload executed. Buffer pool is ready to run. | |
| Explanation |
All preload records were processed. The buffer pool is unlocked and Natural can access that 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).
This section describes problems that may occur when using the Natural buffer pool and how to solve them.
It is assumed that you are familiar with the UNIX commands
ipcs and adb.
The following are typical command output examples, with an explanation of what went wrong during execution.
Either Natural or the Natural Buffer Pool Monitor (NATBPMON utility) 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 Natural Buffer Pool Monitor, and the buffer pool is not active.
You try to start Natural with the following command:
natural bp = sag
The following message appears:
Natural Startup Error: 16 Unable to open Buffer Pool, Buffer Pool error: "unexpected system call error occurred " (20) Global shared memory could not be attached.: shmkey = 11111111 Operating System Error 2 - No such file or directory
You try to start the Natural Buffer Pool Monitor with the following command:
natbpmon bp = sag
When you enter the WHO command at the
NATBPMON prompt, the following message appears:
Buffer Pool error: unexpected system call error occurred (20) Global shared memory could not be attached.: shmkey = 11111111 Operating System Error 2 - No such file or directory
Start the buffer pool service as described in Using the Utility NATBPSRV for Creating the Buffer Pool.
Use the UNIX command ipcs to verify the
existence of the necessary semaphores and the shared memory:
ipcs -m -s
This results in the following output:
IPC status from /dev/kmem as of Mon 23-MAY-2005 12:03:24.30 T ID KEY MODE OWNER GROUP Shared Memory: m 807 0x4e425031 --rw-rw---- sag natural Semaphores: s 85 0x4e425031 --ra-ra---- sag natural
Note:
The above output was edited to exclude memory segments and
semaphores that do not belong to the Natural buffer pool.
If you cannot find a shared memory segment or a set of semaphores with the key you assigned them, the buffer pool was not started.
The Natural buffer pool and a Natural utility are not of the same Natural version.
If a utility tries to use the buffer pool, the utility and buffer pool versions are checked for equality. If they differ, the access is denied and an error message is output.
You try to start Natural and the following message appears:
Natural Startup Error 16: Unable to open buffer pool. Buffer pool error: "Buffer pool does not correspond with your version of Natural"(25). Internal version of buffer pool is 0 but requested internal version is 1.
You try to start the Natural Buffer Pool Monitor and the following message appears:
Buffer pool error: Buffer pool does not correspond with your version of Natural (25). Internal version of buffer pool is 0 but requested internal version is 1.
Verify that your Natural version corresponds to your buffer pool version number and that the internal buffer pool version (BP version) is also correct. Restart the buffer pool with the same version as Natural but make sure that no other users are active.
Important:
The internal buffer
pool version number (BP version) can vary in between service pack
releases (third digit of the product version number). For example, a buffer
pool that has been initiated using Natural
Version
vrs cannot be used with Natural Version
vr(s+1) and vice versa.
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:
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.
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.
To restart the buffer pool, call the file natstart.bsh from a sufficiently privileged account.
If you have super user rights, you can use the FORCE option of the
SHUTDOWN command:
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).
To restart the buffer pool after successful execution of the
SHUTDOWN FORCE command, call the file
natstart.bsh from a
sufficiently privileged account.
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:
Use the UNIX command ipcs to find out the
status of the buffer pool's shared memory and semaphores:
ipcs -a -m
In the column NATTCH of the output of an
ipcs -m -a command, you can see the number of
processes currently attached to a shared memory segment. For example:
IPC status from /dev/kmem as of Mon May 23 12:15:38.39 2002 T ID KEY ... OWNER GROUP ... NATTCH SEGSZ Shared Memory: m 707 0x4e425031 ... sag natural ... 7 153600
It is highly probable that the number of processes attached to shared
memory incorporates a Natural nucleus or the NATBPMON utility
currently running. Inform the users who run these processes and ask them to
terminate their sessions or terminate them yourself by using the UNIX command
kill once you have found out their process IDs using
the ps command.
Once you are sure that no one is using the buffer pool for important
work, its resources can be deleted by using the UNIX command
ipcrm. For example:
ipcrm -M 0x4e425031 -S 0x4e425031
The values specified for the -M and -S
options must be those that were specified inside the parameter file used to
start the buffer pool.
Be careful when you delete shared memory and semaphores using the
UNIX command ipcrm. If you accidentally delete the
wrong resource, this might have a serious impact on other software products
running on your computer.
The result of deletion can be verified by using the UNIX command
ipcs again.
If there are still some memory segments or message queues displayed, they could belong to other software, or they are marked for deletion because some other process is still attached to them.
If the buffer pool cannot be started after removing the shared memory and semaphores, you should consider either rebooting your computer or contacting Software AG Support.