Glossary entries exist beginning with the following letters:
Calculated by the nucleus, Adabas buffer efficiency is the number of requested reads divided by the number of actual reads.
Adabas Caching can be activitated if the Adabas buffer efficiency drops
below a certain setting using the
CDEMAND
parameter.
Adabas Caching is implemented by the ADACSH module. The ADARUN
parameter CACHE=YES is used to indicate that the ADACSH
module is to be loaded during Adabas session initialization. RABN ranges or
files may be predefined using ADACSH session parameters or dynamically added or
modified using the ADACSH operator commands.
For more information, see the ADACSH Module.
Cache space, as used within Adabas Caching, is a logical amount of memory available for caching a specific type of Adabas RABN in a specific type of memory or cache.
Cache spaces can be defined in extended memory, data spaces, hiperspaces, and virtual 64 storage. Once defined, cache areas are allocated dynamically as RABNs move to and from the cache areas and to and from the Adabas buffer pool.
For more information, see Adabas Caching Configuration.
The maximum size of the storage that may be allocated for a given
cache space is determined by the CMAXCSPS parameter and
the CASSOMAXS and CDATAMAXS
parameters:
CMAXCSPS · CDATAMAXS or CMAXCSPS · CASSOMAXS
When space is required for a RABN range or file, ADACSH allocates an
area of storage in the type of cache requested (extended memory, data space,
hiperspace, or virtual 64) with a size of CASSOMAXS or
CDATAMAXS, depending on the type of RABN being cached.
When this space is exhausted, another area of storage is allocated until the
maximum number of areas has been allocated as specified by
CMAXCSPS.
Cache spaces for caching of Work RABNs are allocated in one block
according to the Work caching parameters (CWORKSTORAGE,
CWORK2FAC, CWORK3FAC).
Performance gains may be realized by providing a sufficient number of
cache space areas (CMAXCSPS) to accommodate the
database's working set; that is, the set of Associator and Data Storage blocks
accessed during the Adabas session. This effectively reduces the physical read
I/O to one EXCP per block used.
Note:
In versions of Adabas Dynamic Caching prior to 7.1, a cache space
area was used for a single RABN range only. A single cache space area is now
used for multiple RABN ranges. For best performance, it is therefore advisable
to use fewer, larger cache space areas than were used prior to version 7.1. The
maximum number of cache space areas possible is currently
16.
When specifying RABNs to be cached, CSN is the RABN Range ID that will be assigned to the new RABN range.
This was previously called the cache space number (CSN). For compatibility, the CSN terminology has been retained; however, the CSN now identifies the RABN Range ID to be used as there is no longer a direct correlation between cache spaces and RABN ranges.
For more information, see RABN Range ID.
Adabas Caching provides for caching RABNs globally by RABN range, or at the file level, caching all RABNs associated with a particular file or range of files. File-level caching and global caching for Associator and Data Storage are mutually exclusive in that only one or the other mechanism may be used.
For more information, see Adabas Caching Configuration.
Files can be prioritized by assigning a class of service which determines the percentage of the maximum available cache space that a given file can use and when the file's RABN blocks will be purged from the cache.
For more information, see Adabas Caching Configuration.
Execute channel program (UPAM SVC for BS2000).
Dynamic caching augments the Adabas buffer manager by reducing the number of read EXCPs to the database, thereby permitting maximum use of the available operating system facilities without monopolizing valuable virtual memory resources.
Write EXCPs are always issued to maintain the integrity of the database.
File-level caching refers to the process of caching RABNs based on the file with which they are associated.
For more information, see Adabas Caching Configuration.
Global caching refers to the process of caching a RABN as part of a range of RABNs. A number of different RABN ranges can be specified. They are then cached at the appropriate time when encountered in the running system.
For more information, see Adabas Caching Configuration.
User-specified RABNs (blocks) can be cached or "fenced" to make them readily accessible when demand arises, even though the activity against them is not sufficient to keep them in the active buffer pool. RABN-fencing reduces the required I/O response time if the Adabas nucleus needs to reread those RABNs.
For more information, see Adabas Caching Configuration.
For many commands, it is necessary to identify the RABN range or file / file range to which the command applies.
When global caching is active, each RABN range defined is allocated a unique ID number up to and including 65,535. This number may be used to identify the RABN ranges uniquely.
When file-level caching is active, each file number is unique and is used to identify the subject of an operator request. One or more RABN ranges may be associated with a file; each is given a unique RABN Range ID within the context of that file; however, these cannot be addressed individually and operator commands may only be issued to the file or file range as a whole.
For more information, see Adabas Caching Configuration.
When processing serial Adabas commands (for example, Read
Logical, Read Physical,
Histogram, and searches using nondescriptors) with
the read-ahead caching option, a single EXCP is issued to read all the
consecutive Associator and/or Data Storage blocks that reside on a single track
of the disk device. The blocks are kept in cache and are immediately available
when the nucleus requests the next block in a sequence. This feature may
enhance performance by reducing the number of physical read I/Os for a 3380
Associator by as much as 18:1.
For more information, see the parameter
CBUFNO.
Caching may be specified for Associator RABNs, Data Storage RABNs, and Work RABNs:
For global caching, different ADARUN parameters (and operator
commands) are available to specify caching for Associator RABNs
(CASSOxxx) and Data Storage
RABNs (CDATAxxx).
For file-level caching, the terms of the CFILE parameter allow you to select the RABN types to cache.
RABNs for Work parts 2 and 3 are specified for caching using the
CWORKSTORAGE, CWORK2FAC, and
CWORK3FAC parameters for both global and file-level
caching.
In addition to the caching module ADACSH, the online cache-maintenance application SYSACF is available from the Adabas Online System (AOS) entry screen. Selecting the application from the AOS entry menu transfers you to the SYSACF main menu, which contains options for maintaining the Adabas caching environment.
For more information, see Adabas Caching Online Services.
