Probably the biggest issues with database performance come as a result of poor database design and missing indexes.
数据库性能的最大问题可能源自于不良数据库设计和缺失索引。
Common issues include ill-written queries, missing indexes, and excessive Numbers of database requests per operation.
常见的问题包括编写得有毛病的查询、遗漏了索引以及每个操作中过量的数据库请求。
Given these bleak statistics, it's likely that your site has many pages missing from the search indexes, and those pages can never be found.
既然这个比例如此低，您的站点中很可能有许多页面没有被编入索引，因此这些页面不可能被搜索到。
Sparse indexes boost performance when searching by a field that is often missing within a collection.
Sparse索引在所检索的字段并非经常出现在集合中时能提升性能。
Covering indexes allow data storage within the index itself while sparse indexes exclude documents that do not contain the missing field.
Covered索引允许在索引本身里存储数据，而Sparse索引则会排除掉不包含索引字段的文档。
Covering indexes allow data storage within the index itself while sparse indexes exclude documents that do not contain the missing field.
Covered索引允许在索引本身里存储数据，而Sparse索引则会排除掉不包含索引字段的文档。
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