要解决这些问题，可以删除无关的索引，添加一个新的索引，或者在某些表中周期性地清除大量过期的数据。
To solve these problems, drop the extraneous index, add a new index, or periodically clean out the large volume of obsolete data in some tables.
理想情况下，索引提供了足够多的信息，可以只读入所需要的行，但是有时候查询(设计不佳或数据本性使然)需要读取表中大量数据。
Ideally, the indexes provide enough information to read in only the needed rows, but sometimes queries (through poor design or the nature of the data) require large chunks of the table to be read.
此处的“大量”可能意味着10%到20%的表和索引数据都受到了影响。
"Extensive" in this case may mean that 10 to 20 percent of the table and index data has been affected.
尽管在搜索引擎中文件多是以大数据集的方式出现，但是在其它很多应用中，大量小文件的访问是很普遍的。
Although in search engine we mainly process large data sets, in other applications we also need to process a large mount of small files.
聚集索引通常可加快UPDATE和DELETE操作的速度，因为这些操作需要读取大量的数据。
UPDATE and DELETE operations are often accelerated by clustered indexes because these operations require large amounts of data to be read.
聚集索引通常可加快UPDATE和DELETE操作的速度，因为这些操作需要读取大量的数据。
UPDATE and DELETE operations are often accelerated by clustered indexes because these operations require large amounts of data to be read.
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