Importance

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Abstract

Apparatus and method for reading data pages in a transaction processing system without locking the pages are disclosed. The system maintains a Global.sub.-- Committed.sub.-- LSN identifying the oldest uncommitted transaction accessing any of the data, and Object.sub.-- Committed.sub.--LSNs identifying the oldest uncommitted transactions accessing particular files, tables and indexes. Each data page includes a Page.sub.-- LSN identifying the last transaction to have updated the page. To read a page, a transaction first latches the pages, and compares the page's Page.sub.--LSN with the Global.sub.-- Committed.sub.-- LSN, or with the page's respective Object.sub.-- Committed.sub.-- LSN. If the Page.sub.-- LSN is older than the Committed.sub.-- LSN with which it was compared, then the transaction reads the page without locking it, since there can be no uncommitted transaction in process which might have updated the page's data. However if the Page.sub.-- LSN is younger than the Committed.sub.--LSN, the page is locked before being read.

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First Claim