Error detection/correction and fault detection/recovery – Data processing system error or fault handling – Reliability and availability
Reexamination Certificate
1998-10-29
2001-07-03
Ray, Gopal C. (Department: 2181)
Error detection/correction and fault detection/recovery
Data processing system error or fault handling
Reliability and availability
C712S228000, C707S793000
Reexamination Certificate
active
06256751
ABSTRACT:
TECHNICAL FIELD
This invention relates, in general, to restoring checkpointed processes and, in particular, to leaving attributes of external data referenced by the checkpointed processes unrestored when the checkpointed processes are restored.
BACKGROUND ART
A requirement of any robust computing environment is to be able to recover from errors, such as device hardware errors (e.g., mechanical or electrical errors) or recording media errors. In order to recover from some device or media errors, it is necessary to restart a process, either from the beginning or from some other point within the process.
To facilitate recovery of a process, especially a long running process, intermediate results of the process are taken at particular intervals. This is referred to as checkpointing the process. Checkpointing enables the process to be restarted from the last checkpoint, rather than from the beginning of the process.
When a process is restarted, it is restored to the state it was in when the checkpoint was taken. Thus, any and all changes subsequent to the last checkpoint are undone. This includes any changes that have been made to attributes of external data, such as external functions and/or external variables, referenced by the process. Once the process is restored to its former state, it continues to execute from that point.
Based on the foregoing, a need exists for a restore capability that does not require that all information be restored to the point at which the checkpoint was taken. That is, a need exists for a capability that allows selected information to remain unrestored. In particular, a need exists for a restore capability that enables attributes of external data to remain unrestored, even though other components of the process are being restored.
SUMMARY OF THE INVENTION
The shortcomings of the prior art are overcome and additional advantages are provided through the provision of a method of restoring checkpointed processes that have references to external data. The method includes, for instance, restarting a process on a computing unit from a checkpoint taken of the process, wherein the process includes a reference to an external datum. Further, the method includes restoring the process using information obtained from the checkpoint. The restoring leaves one or more attributes of the external datum unrestored.
In one example, the external datum includes one of an external function and an external variable.
Further, the process is restarted on a computing unit, which is different from the computing unit used to take the checkpoint. In another example, the process is restarted on the same computing unit used to take the checkpoint.
In yet another embodiment of the present invention, the one or more attributes are located in a data section of the process, and the restoring includes restoring the data section except for the one or more attributes stored therein.
In one example, the restoring of the data section includes, for instance, obtaining a beginning address of a table of contents of the data section, wherein the table of contents includes the one or more attributes; obtaining an ending address of the table of contents; restoring information located in the data section before the beginning address of the table of contents, if any; and restoring information located in the data section after the ending address of the table of contents, if any.
In another aspect of the present invention, a system of restoring checkpointed processes that have references to external data is provided. The system includes, for instance, means for restarting a process on a computing unit from a checkpoint taken of the process, wherein the process includes a reference to an external datum; and means for restoring the process using information obtained from the checkpoint, wherein the means for restoring leaves one or more attributes of the external datum unrestored.
In yet a further aspect of the present invention, a system of restoring checkpointed processes that have references to external data is provided. The system includes a computing unit adapted to restart a process from a checkpoint taken of the process, wherein the process includes a reference to an external datum. The computing unit is further adapted to restore the process using information obtained from the checkpoint, wherein one or more attributes of the external datum are left unrestored.
In a further aspect of the present invention, an article of manufacture, including at least one computer usable medium having computer readable program code means embodied therein for causing the restoring of checkpointed processes that have references to external data, is provided. The computer readable program code means in the article of manufacture includes, for instance, computer readable program code means for causing a computer to restart a process on a computing unit from a checkpoint taken of the process, wherein the process includes a reference to an external datum; and computer readable program code means for causing a computer to restore the process using information obtained from the checkpoint, wherein the computer readable program code means for causing a computer to restore leaves one or more attributes of the external datum unrestored.
The capabilities of the present invention advantageously enable attributes of external data to remain unrestored, even though a process is being restarted from a checkpoint. This allows a process to be restored and to still reflect some aspects of the current operating environment. Thus, greater flexibility is provided for the restarted process. For example, a process can be restarted on a different computing unit than the one used to take the checkpoint, and the new computing unit is reflected in the process, rather than the old computing unit.
Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention.
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Agbaria Adnan M.
Meth Kalman Zvi
Moreira Jose
Naik Vijay
Gonzalez, Esq. Floyd A.
Heslin & Rothenberg, P.C.
International Business Machines - Corporation
Ray Gopal C.
Schiller, Esq. Blanche E.
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