Eliminate I/O Bottlenecks with OPTI-CACHE
In recent years, processor speed and disk capacity have vastly increased. But these innovations only go so far, since it still takes too long to access data on disk. As you know too well, I/O is the major bottleneck in VSE systems. When a job or application puts demands on the I/O subsystem, you get sluggish response times and long run-times.
Finally, there is a solution to I/O bottlenecks: Barnard Software's OPTI-CACHE. This revolutionary product provides software and hardware cache management at the dataset and volume level, for optimal performance and flexibility. OPTI-CACHE's intelligent cache management means that I/O requests can complete in a fraction of the time they previously took. The result: much faster response times and reduced batch execution times.
Software Cache Management
OPTI-CACHE provides a high-speed virtual storage software cache. Software caching eliminates the I/O subsystem from the loop, so requests can be serviced 200 to 500 times more quickly. This makes a noticeable difference in response times. OPTI-CACHE is designed to automatically decide which datasets have the best cache characteristics, and to cache data only from those datasets. And you can fully customize the product to meet your specific needs. OPTI-CACHE even detects sequential access to datasets automatically and reads ahead a user-specified number of trackswith just one I/O. Multi-track read-ahead greatly improves the performance of these datasets. Sites using OPTI-CACHE have observed particular improvements in the performance of libraries. OPTI-CACHE reduces the number of I/Os needed to load members from libraries. OPTI-CACHE uses read-ahead and write-through caching strategies. With its read-ahead caching, a full track of data is loaded into the cache when an I/O request is satisfied. This increases the chance of another request being satisfied with already-cached data. Write-through caching updates data in the cache as the write is being done.
Hardware Cache Management
For sites with IBM 3990 (or compatible) hardware, VSE provides hardware caching. But VSE's hardware caching can be controlled only at the volume level. Thus, VSE does not try to determine whether datasets have appropriate cache characteristics. OPTI-CACHE, instead, provides automated and manual dataset-level controls for managing 3990 hardware. Datasets that you do not want cached, as well as those with poor cache characteristics, are not cached. OPTI-CACHE also lets you define datasets with sequential status. When accessing these, OPTI-CACHE tells the 3990 hardware that sequential access is occurring, so the controller can perform automatic read-ahead of the next two tracks. The controller also destages tracks after they have been read, to keep data in large datasets from flooding the cache.
Intelligent Cache Management
Even the best cache strategies can hamper performance if they cache data with poor cache characteristics. That's why OPTI-CACHE selects for caching only datasets with good cache characteristics. These include:
You can tell OPTI-CACHE to always or never cache particular datasets. All others keep a may cache status, which is adjusted periodically (normally every 100 I/O requests). Once the dataset exhibits poor cache characteristics, it is not cached for a while (normally 500 I/O requests); then it is reevaluated. Thus, as dataset usage changes, OPTI-CACHE dynamically adjusts. You control the criteria OPTI-CACHE uses for adjustment, including evaluation intervals.
For maximum performance improvements, OPTI-CACHE monitors each extent of a dataset separately. This lets the product distinguish between data and indexes and between multiple data extents with different cache characteristics.
OPTI-CACHE also monitors system paging. During periods of high system paging (by your site's standards), OPTI-CACHE deactivates one cache buffer every 15 seconds until up to half of the cache buffers have been deactivated. Once paging rates return to normal levels, OPTI-CACHE reactivates cache buffers at the same rate.
User Controls
You can control OPTI-CACHE at both the volume and dataset levels for maximum flexibility. OPTI-CACHE's commands let you override default cache statuses. You can tell OPTI-CACHE to always or never cache I/O requested to the dataset. You can also tell it to write-protect the dataset. By default, OPTI-CACHE allows reads and writes, and allows caching of datasets with appropriate cache characteristics.
VSAM Performance Improvements
Most sites find that VSAM does not perform up to par in CICS environments. Allocating many buffers or using local shared resource (LSR) pools for high-activity datasets increases CPU overhead, since VSAM searches its buffers sequentially. For datasets using LSR, OPTI-CACHE's use of full-track I/O effectively adds control interval (CI) read-ahead. Non-shared resources (NSR) deliver better performance for datasets that are accessed sequentially, have split activity, or are heavily used. However, when these datasets are accessed randomly, VSAM always rereads the index record-even if the data record is already in a buffer. And VSAM uses vast amounts of storage to allocate many non-shared resource buffers. When VSAM reads a CI of data, OPTI-CACHE reads the track into the cache and returns the requested CI. Remaining CIs are in the cache and available when requested with no rereading of index records. VSAM buffer pools are, in effect, extended by the size of the OPTI-CACHE partition.
Technical Considerations
OPTI-CACHE runs under VSE/SP, version 3.2 or higher, and VSE/ESA, version 1.1 or higher. The product uses 96K of page-fixed system GETVIS. Also, it requires page-fixable storage within its partition.
To avoid integrity problems, OPTI-CACHE does not automatically cache data on shared DASD. You can, however, fully use OPTI-CACHE while ensuring data integrity. For a dataset used by multiple systems, simply specify that it be write-protected and never cached on non-production systems, and let OPTI-CACHE cache it normally on the production system.
For More Information
To stop I/O bottlenecks, call 1-800-251-OPTI today. We're so confident that OPTI-CACHE will improve your system's performance that we offer a free, 30-day product evaluation.
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