Importance

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Abstract

A data manager of a relational database management system (RDBMS) receives a command, such as a DELETE. As the RDBMS processes this command, an index manager looks at cursor control block information about the scan position (page number, logical key position within page and log sequence number (LSN) of the page) and immediately accesses the corresponding leaf page to do the key deletion. If the page's log sequence number has not changed since the scan was positioned on it, the index manager knows precisely where the key is and deletes it right away. Even if the page's log sequence number has changed, the index manager checks to see if the key is still on the same page. Only if the key is not on that page anymore will the index manager traverse the tree from the root to locate the key. Using this same information, together with a return.sub.-- current flag in the cursor control block, the method can easily determine the next key in the sequence. The return.sub.-- current flag is set when the current key is deleted. If the leaf page's log sequence number has not changed since the deletion and the return.sub.-- current flag is set, the method of the invention establishes that the key which now resides in the same logical position as the previously deleted key is the next key, and may be returned as such. If the LSN is the same and the return.sub.-- current flag is not set, then the next key is returned following locking. If the LSN has changed but the key is still bound on the page, the next key is searched and located, a lock is asserted (if necessary) and the key is returned. Only if the page logical sequence number has changed and the previous key is no longer bound on the page will the index manager traverse the index tree to locate the next key, lock the key (if necessary) and return it.

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First Claim