IBM 86884RX Installation Guide - Page 45
In-memory databases, memory and access them with little or no paging overhead. This is often done
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Database applications with memory-sensitive workloads that require working data sets larger than 4 GB to be loaded in memory will benefit from the larger memory support of the 64-bit platform. The following is an example from the field. Microsoft SQL Server Enterprise Edition uses AWE memory only for the buffer pool. The AWE (Advanced Windowing Extensions) API allows applications that are written to use the AWE API to access more than 4 GB of RAM (basically anything between 4 GB and 64 GB). However, due to the AWE mapping overhead, it is not practical to try to use it for sort areas, procedure cache, or any other type of work area. Many applications do make heavy use of these areas and may not benefit by having the large buffer pool. The most efficient solution in such cases is to move the applications on to a 64-bit database server, which can access memory area above 4 GB much more efficiently without AWE's overhead. Users will see a reasonable performance improvement on a 64-bit implementation over a 32-bit implementation. Through the 64-bit memory paths, all memory operations move twice as much data at the same speed as the 32-bit platform. The database server will also benefit from a larger 3 MB third-level and 64 MB XceL4 cache. With such large cache, the need to go to memory or disk for database transaction elements is greatly reduced and this directly implies a performance increase, faster access to data, and improved throughput. Itanium 2 systems are likely to be able to hold database transaction records in cache during the entire transaction, which enables the I/O portion of the transaction to occur at speeds faster than memory access. In-memory databases Architectures with 64-bit addresses can store reasonably large databases in memory and access them with little or no paging overhead. This is often done for databases that are constantly being accessed and for databases that serve as the basis for complex analysis. The theoretical maximum of 16 Exabytes for memory has not yet been tested, but multi-Gigabyte databases are frequently run on 64-bit machines. A major challenge to providing high-performance access to database information is the time it takes to access disk drives. When disk access is required, disk access times add what can be an intolerable delay to efficient information access and utilization. Access to disk is typically hundreds to thousands times slower than access to memory. Today, the disk access time challenge can be overcome. The price of random access memory has come down to affordable levels for many systems. This price Chapter 2. Positioning 31
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