Methods To Perform Disk Writes In A Distributed Shared Disk System Needing Consistency Across Failures
First Claim
1. A method for managing versions of a data item, the method comprising the steps of:
- when a dirty version of a data item is transferred from a first node to a second node while a being-written version of the data item is being written to persistent storage, performing the steps of;
communicating version information about the being-written version to the second node; and
based on the version information, the second node preventing any version of the data item that belongs to a first set of versions from being merged with any version of the data item that belongs to a second set of versions;
wherein the first set of versions includes all versions of the data item within the second node that are at least as old as the being-written version; and
wherein the second set of versions includes versions of the data item within the second node that are newer than the being-written version.
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Abstract
Techniques are provided for managing caches in a system with multiple caches that may contain different copies of the same data item. Specifically, techniques are provided for coordinating the write-to-disk operations performed on such data items to ensure that older versions of the data item are not written over newer versions, and to reduce the amount of processing required to recover after a failure. Various approaches are provided in which a master is used to coordinate with the multiple caches to cause a data item to be written to persistent storage. Techniques are also provided for managing checkpoints associated with the caches, where the checkpoints are used to determine the position at which to begin processing recovery logs in the event of a failure.
99 Citations
16 Claims
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1. A method for managing versions of a data item, the method comprising the steps of:
when a dirty version of a data item is transferred from a first node to a second node while a being-written version of the data item is being written to persistent storage, performing the steps of; communicating version information about the being-written version to the second node; and based on the version information, the second node preventing any version of the data item that belongs to a first set of versions from being merged with any version of the data item that belongs to a second set of versions; wherein the first set of versions includes all versions of the data item within the second node that are at least as old as the being-written version; and wherein the second set of versions includes versions of the data item within the second node that are newer than the being-written version. - View Dependent Claims (2, 3, 4, 5)
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6. A method for managing past images of a data item, the method comprising the steps of:
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estimating a likelihood that a first past version of a data item will soon be written to persistent storage or covered by a write to persistent storage; if the estimated likelihood is exceeds a particular threshold, then storing a second past version of the data item separate from the first past version of the data item; and if the estimated likelihood falls below a particular threshold, then merging the second past version of the data item with the first past version of the data item. - View Dependent Claims (7, 8)
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9. A computer-readable medium carrying instructions for managing versions of a data item, the instructions comprising instructions for performing the steps of:
when a dirty version of a data item is transferred from a first node to a second node while a being-written version of the data item is being written to persistent storage, performing the steps of; communicating version information about the being-written version to the second node; and based on the version information, the second node preventing any version of the data item that belongs to a first set of versions from being merged with any version of the data item that belongs to a second set of versions; wherein the first set of versions includes all versions of the data item within the second node that are at least as old as the being-written version; and wherein the second set of versions includes versions of the data item within the second node that are newer than the being-written version. - View Dependent Claims (10, 11, 12, 13)
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14. A computer-readable medium carrying instructions for managing past images of a data item, the instructions comprising instructions for performing the steps of:
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estimating a likelihood that a first past version of a data item will soon be written to persistent storage or covered by a write to persistent storage; if the estimated likelihood is exceeds a particular threshold, then storing a second past version of the data item separate from the first past version of the data item; and if the estimated likelihood falls below a particular threshold, then merging the second past version of the data item with the first past version of the data item. - View Dependent Claims (15, 16)
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Specification