Reserving extra memory, for example to hold the contents of a cursor, may be expensive. If the cache is full, one or more pages may have to be written to disk to make room for new pages. Some pages may need to be re-read to complete a subsequent operation. In this situation, SQL Anywhere associates a higher cost with execution plans that require additional buffer cache overhead. This cost discourages the optimizer from choosing plans that use work tables. However, the optimizer is careful to use memory where it improves performance. For example, it caches the results of subqueries when they will be needed repeatedly during query processing.
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