公开(公告)号：US4631673A

公开(公告)日：1986-12-23

申请号：US693500

申请日：1985-01-22

申请人： Laura M. Haas ,  Bruce G. Lindsay

发明人： Laura M. Haas ,  Bruce G. Lindsay

IPC分类号： G06F12/00 ,  G06F7/22 ,  G06F17/30 ,  G06F15/20

CPC分类号： G06F17/30595 ,  Y10S707/99939 ,  Y10S707/99952

摘要： A method for refreshing a relational data base snapshot manifest in the form of remote read-only copies of selected portions of a base table. The method takes advantage of the fact that each tuple of the base table has a unique identifier TID associated therewith from the time the record is inserted until it is deleted. The TID references the physical location of the tuple within its relation. Two system-maintained fields are added to the base table. These are PREVTID and update ID. One system-maintained column is required in the snapshot table, i.e. BASE TID. Lastly, a column in the catalog of the snapshot is also maintained, i.e. SNAPHIGH.When the refresh of the snapshot table is required, a single scan of the base relation, in ascending TID sequence, is performed on the base table. The scan produces a series of messages which contain the incremental changes required to update the snapshot table to the current state of the base relation. Upon receipt of the messages at the snapshot table site, a single skip sequential pass across the snapshot in BASE TID sequence is performed to apply the incremental changes. This refreshes the snapshot table to the required state.

摘要翻译： 用于以基表的所选部分的远程只读副本的形式刷新关系数据库快照清单的方法。 该方法利用了从插入记录直到被删除的时间之后，基表的每个元组具有与其相关联的唯一标识符TID的事实。 TID在其关系中引用元组的物理位置。 两个系统维护的字段被添加到基表中。 这些是PREVTID和更新ID。 快照表中需要一个系统维护的列，即BASE TID。 最后，还保留快照目录中的列，即SNAPHIGH。 当需要刷新快照表时，在基表上执行以升序TID序列的基本关系的单次扫描。 扫描产生一系列消息，其中包含将快照表更新为基本关系的当前状态所需的增量更改。 在快照表站点接收到消息后，将执行BASE TID序列中快照的单次跳过顺序，以应用增量更改。 将快照表刷新到所需状态。