Browse Prior Art Database

Checkpoint During Merge with Write In Place

IP.com Disclosure Number: IPCOM000077763D
Original Publication Date: 1972-Sep-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Parkinson, J: AUTHOR

Abstract

To reconstruct a system of chained blocks used for sequences being merged with a write-in-place technique, valid copies of every record and every link address are needed.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 53% of the total text.

Page 1 of 2

Checkpoint During Merge with Write In Place

To reconstruct a system of chained blocks used for sequences being merged with a write-in-place technique, valid copies of every record and every link address are needed.

A buffer control block is initialized when an input buffer is filled, with the input's disk address. When the buffer is emptied, the control block is linked to the output buffer which received the input buffer's last record. When the output operation performed on the output buffer is complete, then control blocks chained to the output buffer are transferred to the output buffer with the next newest incomplete output operation. When no such output buffer exists, the control block is linked onto a queue of blocks, each of which now contains a disk address which is available for output. However, the address of the last block of an input sequence is not placed on the queue. As soon as the control block is placed on the queue, the link is available for saving in a new output block.

The queue of output addresses is primed with M+3x+2 addresses, where M is the merge order, and x the maximum number of write requests that can be issued between the requesting and completion of another write operation. The first x blocks written can contain null saved links. The next M contain pointers to the first blocks of the M input sequences. Saved links can be copied thereafter.

After being called, the restart routine must identify the most recently commenced output sequence. This can be traced until a break point is reached; that is, a link which does not point to a new block of the same sequence. In order that this condition may be recognized, sequences should be numbered, and...