push-downs

英

美

(push-down 的复数) n. 推下, 迭式存储器
[计] 下推
push-down 的复数

By reducing I/ O costs, index push-downs eliminate fact table rows more efficiently than bit-vector push-downs, but their processing cost is higher.
通过减少I/O成本，索引下推可以比位向量下推更有效地消除事实表行，但处理成本比较高。
For multiple index push-downs, multi-index scan is used to combine RIDs from different index scans, then skip-scan on the fact table is performed.
对于多索引下推，多索引扫描用于组合来自不同索引扫描的RID，然后就可以执行对事实表的跳跃式扫描了。
The optimizer chooses the best number of push-downs based on cost estimation, such that the work required to perform push-down does not outweigh the benefit for applying the push-down filter.
优化器根据成本估算选出最佳的下推次数，以便执行下推所需的工作量不会超出应用下推过滤的好处。
Multiple-bit vectors can be used for multiple bit-vector push-downs.
多位向量可用于多位向量下推。
Index push-downs require only a single-column index on the fact table, although they can use a multi-column index if the required foreign-key column is the first key in the index.
索引下推只需要事实表的单列索引，虽然在所需的外键列是索引的第一个键的情况下可以使用多列索引。