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Browse Prior Art Database

Record Read Exclusive

IP.com Disclosure Number: IPCOM000076338D
Original Publication Date: 1972-Feb-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Frazer, DK: AUTHOR [+2]

Abstract

The described function allows a user to gain exclusive control of a single record on a direct access device, while maintaining device availability to all CPU's connected to the device. This function uses a bit in the predata portion of a disk record to indicate the record is reserved. Two Channel Command Words (CCW's) are used to reserve and release the records. This avoids the creation of a subsystem of an access method to keep track of records enqueued upon through software, with the hardware performing this function with greater reliability. In a Shared Direct Access Storage Device (DASD) environment, files could be updated from each central processing unit (CPU) at the same time without conflict, as contrasted to a solution which makes the entire file unavailable to the other CPU while one is updating it.

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Record Read Exclusive

The described function allows a user to gain exclusive control of a single record on a direct access device, while maintaining device availability to all CPU's connected to the device.

This function uses a bit in the predata portion of a disk record to indicate the record is reserved. Two Channel Command Words (CCW's) are used to reserve and release the records. This avoids the creation of a subsystem of an access method to keep track of records enqueued upon through software, with the hardware performing this function with greater reliability. In a Shared Direct Access Storage Device (DASD) environment, files could be updated from each central processing unit (CPU) at the same time without conflict, as contrasted to a solution which makes the entire file unavailable to the other CPU while one is updating it.

Fig. 1 shows the logic required to obtain exclusive control of a record. Any Read request for a reserved record is rejected. For Read requests requiring exclusive control, the reserved bit is written on the disk to prevent further access to the record.

Fig. 2 shows the logic required to release exclusive control of the record. The reserved bit is turned off by writing on the disk and the record may optionally be rewritten at the same time.

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