Large I/O and performance

You can configure the default cache and any named caches you create for large I/O by splitting a cache into pools. The default I/O size is 2K, one Adaptive Server data page.

NoteReference to Large I/Os are on a 2K logical page size server. If you have an 8K page size server, the basic unit for the I/O is 8K. If you have a 16K page size server, the basic unit for the I/O is 16K.

For queries where pages are stored and accessed sequentially, Adaptive Server reads up to eight data pages in a single I/O. Since the majority of I/O time is spent doing physical positioning and seeking on the disk, large I/O can greatly reduce disk access time. In most cases, you want to configure a 16K pool in the default data cache.

Certain types of Adaptive Server queries are likely to benefit from large I/O. Identifying these types of queries can help you determine the correct size for data caches and memory pools.

In the following examples, either the database or the specific table, index or LOB page change (used for, text, image, and Java off-row columns) must be bound to a named data cache that has large memory pools, or the default data cache must have large I/O pools. Types of queries that can benefit from large I/O include: