December 2012
Intermediate to advanced
572 pages
13h 8m
Chinese
Content preview from HBASE技術手冊
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第八章
在此同時，它也會記錄那些刪除標記。當它掃描當前列的
KeyValue
時，可能會碰到這些
刪除標記，那些時間戳記小於等於該刪除標記的記錄，都會被認為是已經清除掉了。
圖 8-10 中顯示了
邏輯上的行
（
logical row
），它組成了一個
KeyValue
清單，某些儲存在
相同的儲存檔上，某些則在其他儲存檔中，它延伸了多個 column family。由於時間戳記
或者 Bloom 過濾器的排除過程，某些的儲存檔和 memstore 可能會被略過。最後一個儲
存檔中的刪除標記，可能會遮蔽掉所有的記錄，但是它們仍然是同一列的一部分。這些
scanner ─可以用一個指向儲存的箭頭表示—要不是指向檔案中的第一個配對項目，就
是沒有配對項目時，會緊接著所請求的 key 後面。
在呼叫
next()
法期間，只考慮位在適當列的 scanner。內部迴圈將會陸續地從第一到最
後一個儲存體中讀取
KeyValue
，依時間降序排列，直到它們也超出所請求 rowkey 範圍。
對於 scan 的操作，藉著重複呼叫
ResultScanner
的
next()
方法，直到已經找到停止列、
已經到達資料表尾端，或是針對目前的批次（透過 scanner 緩衝設定）已經讀取足夠的
列而停止掃描。
最終的結果是符合指定的 get 或者 scan 操作的一個
KeyValue
實體清單。這個清單會被
回傳給客戶端，客戶端就可以使用 API 方法來存取裡面的所包含的行欄位資料。
Region 的尋查
為了讓客戶端能夠找到控制的特定 rowkey ...
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.