if the anticipated cost of a query is relatively low-say a five-second query about blueberries-a dba will often pay no attention to it.
如果一个查询的预期成本相当低(比如对蓝莓的查询花费5秒),dba往往不会注意它。
if the anticipated cost is high, they tune the statement and the physical design of the database to reduce its anticipated cost, often by adding an index.
如果预期成本很高,他们会调整语句和数据库的物理设计(常常会添加索引),从而降低预期成本。
the first step on determining whether the workover, as designed, is affordable is to calculate the anticipated cost if the repair work and the equipment.