【正文】 Edition, Oct 23, 2022. Overview of Physical Storage Media 物理存儲(chǔ)介質(zhì) ? Magic Disks 磁盤 ? RAID 磁盤陣列 ? Tertiary Storage 第三存儲(chǔ) ? Storage Access 存取 ** ? File Organization 文件結(jié)構(gòu) ** ? Organization of Records in Files 記錄結(jié)構(gòu) ** ? DataDictionary Storage 數(shù)據(jù)字典 ** ? Storage Structures for ObjectOriented Databases 169。Silberschatz, Korth and Sudarshan Database System Concepts 5th Edition, Oct 23, 2022. Storage Hierarchy ?各層 ?存儲(chǔ)速度有數(shù)量級(jí)的差別 ?至少 10倍 慢介質(zhì)以廉價(jià)和容量而頑固地不肯退出歷史舞臺(tái) 169。Silberschatz, Korth and Sudarshan Database System Concepts 5th Edition, Oct 23, 2022. Sequential File Organization ? 適用于 處理 序列性，歷史性 數(shù)據(jù)的場(chǎng)合 ? 按某個(gè)或幾個(gè)屬性 排序 searchkey 169。Silberschatz, Korth and Sudarshan Database System Concepts 5th Edition, Oct 23, 2022. VariableLength Records: Slotted Page Structure 變長(zhǎng)記錄 槽口 存頁(yè)面結(jié)構(gòu) ? Slotted page header contains: 文件頭存 : ? number of record entries 記錄個(gè)數(shù) ? end of free space in the block 回收列表結(jié)束 ? location and size of each record每個(gè)記錄起止 ? 與 光盤目錄的組織 有點(diǎn)相似 169。Silberschatz, Korth and Sudarshan Database System Concepts 5th Edition, Oct 23, 2022. Physical Storage Media (Cont.) ? Flash memory 閃存 ? Data survives power failure 非易逝 ? Data can be written at a location only once, but location can be erased and written to again 可重寫 ? 有限次讀寫 目前質(zhì)量： 110萬次，夠用了 ? Reads are roughly as fast as main memory 讀快 ? 寫稍微慢 ? 貴 ， ? 用于嵌入式設(shè)備 ， 數(shù)字相機(jī) MP3 ? also known as EEPROM (Electrically Erasable Programmable ReadOnly Memory) 169。 managed by the puter system hardware. 快， 易逝， 硬件 ?高速高價(jià) ?設(shè)備 ?低速低價(jià) ?設(shè)備 ?多種 Cache： ?CPU與內(nèi)存 ?內(nèi)存與磁盤 ?OS與 DBMS 169。Silberschatz, Korth and Sudarshan Database System Concepts 5th Edition, Oct 23, 2022. FixedLength Records ? Simple approach: ? Store record i starting from byte n ? (i – 1), where n is the size of each record. ? Record access is simple but records may cross blocks ? Modification: do not allow records to cross block boundaries ? Deletion of record i: alternatives: ? move records i + 1, . . ., n to i, . . . , n – 1 ? move record n to i ? do not move records, but link all free records on a free list 169。Silberschatz, Korth and Sudarshan Database System Concepts 5th Edition, Oct 23, 2022. Clustering File Organization 聚簇文件 ? 不同型但相關(guān)的數(shù)據(jù)放在一起 （舊式大家庭： 幾代同堂 ） ? ., clustering anization of customer and depositor: ? 作這兩各關(guān)系連接時(shí)，快 ? results in variable size records 169。Silberschatz, Korth and Sudarshan Database System Concepts 5th Edition, Oct 23, 2022. Storage Access（存儲(chǔ)