Browse Prior Art Database

Check-on-Access Policy with Deferred Write and Remote Buffer Look-up

IP.com Disclosure Number: IPCOM000106751D
Original Publication Date: 1993-Dec-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 2 page(s) / 69K

Publishing Venue

IBM

Related People

Dan, A: AUTHOR [+2]

Abstract

Disclosed is an approach to integrate check-on-access coherency policy with deferred write policy for savings in write I/O and remote buffer look-up for savings in read I/O, in a data sharing environment.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Check-on-Access Policy with Deferred Write and Remote Buffer Look-up

      Disclosed is an approach to integrate check-on-access coherency
policy with deferred write policy for savings in write I/O and remote
buffer look-up for savings in read I/O, in a data sharing
environment.

      In contrast to Lock retention based coherency policies, under
the Check-on-Access policy a node doesnot retain any lock brought in
by an executing transaction after it has committed [1,2,3].
Therefore, under this policy the updated pages are propagated to the
disk at the transaction commit point before all locks are released.
In this invention disclosure, a method is described that extends the
basic check-on-access policy by maintaining additional information in
the Global Lock Manager (GLM), for the purpose of deferred write, and
remote buffer look up.  It is assumed that there is no shared buffer
in the system, and hence, the updated pages for which the write
propagation to the shared disk are deferred, must be obtained from
the nodes which have the latest copy of these pages.

      Under the basic check-on-access policy, the GLM maintains a bit
vector for each page corresponding to all the nodes in the system,
such that each bit represents the validity of the copy of that page
if present in the buffer of the corresponding node.  The bit is set
to one if the page in that node is valid; Otherwise, the bit is set
to zero.  At the transaction commit time, if a page is updated by the
committing transaction, the bits corresponding to all other nodes
except the updating node for this page are set to zero, representing
them invalid.  No explicit message is sent to other nodes for
invalidating the copies of that page in the remote buffers.  At a
later point, if an executing transaction accesses this page, its
local node will request a lock on this page to the GLM, and the GL...