Performance and Storage Considerations (217)

Key compression can lead to a huge saving in space, letting you store more keys in
each index block, which can lead to less I/O and better performance.

Although key compression reduces the storage requirements of an index, it can
increase the CPU time required to reconstruct the key column values during an index
scan. It also incurs some additional storage overhead, because every prefix entry has
an overhead of 4 bytes associated with it.

效能以及儲存上的考慮
1. 可以在索引塊中儲存跟過的索引鍵 ，減少I/O ，提高效能 ，節省空間
2. 當執行索引掃描時 ，要重構鍵值 ，因此增加了 CPU 的負擔
3. 鍵壓縮也會導致額外的儲存開銷 ，因為每個字首需要4位元組的管理開銷

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