EP0303231A2
Expired / Lapsed
EP
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Method and device for enabling concurrent access of indexed sequential data files
Assignee: Wang Laboratories Inc
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Filing: 1988-08-09
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Granted: —
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Expires: 2008-08-09
Abstract
Abstract An indexed sequential file is made accessible for random or sequential reading of records while allowing concurrent modification to the file. Each ordered group of records in the file is associated with timestamps referencing a deletion time of the group and the time that the group was last modified. During a current search in a group for a desired record, the timestamp referencing a deletion time of the group is compared to a search time established at the beginning of the search. For a sequential reading the timestamp referencing a last modification time of a group containing the desired record is compared to a respective timestamp corresponding to the reading of the preceeding record. The comparisons provide indications of whether the group to which the desired record belongs is currently the group to be searched. The most recently modified and deleted groups are stored in cache memory. When the cache memory is full, an incoming group and respective timestamps replaces the least recent or least likely to be used group and respective timestamps. The most recent timestamps of replaced groups' timestamps are saved in local memory and are used in the comparisons for groups not currently in the cache.
Inventors
- 👤 Arthur Grand
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-26 06:30
CPC Classifications
G; G06; G06F; G06F16/00; G06F16/20; G06F16/22; G06F16/2228; G06F16/2246; Y; Y10; Y10S; Y10S707/00; Y10S707/99931; Y10S707/99932; Y10S707/99938
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
117 words
A method of sequentially accessing and reading a list of succeeding ordered elements while concurrently allowing the list to be modified, the method being characterized by the steps of: providing a tree-structure data file for the elements, the tree-structure having a plurality of nodes defined by ordered subgroups of the ordered elements, the nodes linked to each other, in order, by associated pointers; assigning timestamps to part of the tree structure; saving an indication of an element which was last read and a timestamp corresponding to the last read part of the tree; and comparing a current timestamp assigned to the last read part of the tree structure with the saved timestamp before reading a succeeding element.
Claim 2
Independent Claim
117 words
A method of sequentially accessing and reading a list of succeeding ordered elements while concurrently allowing the list to be modified, the method being characterized by the steps of: providing a tree-structure data file for the elements, the tree-structure having a plurality of nodes defined by ordered subgroups of the ordered elements, the nodes linked to each other, in order, by associated pointers; assigning timestamps to part of the tree structure; saving an indication of an element which was last read and a timestamp corresponding to the last read part of the tree; and comparing a current timestamp assigned to the last read part of the tree structure with the saved timestamp before reading a succeeding element.
Claim 3
Dependent Claim
32 words
A method as claimed in Claim 1 and further characterized in that the step of assigning timestamps to part of the tree structure includes assigning timestamps to nodes of the tree structure.
Claim 4
Dependent Claim
39 words
A method as claimed in Claim 2 and further characterized in that the step of assigning timestamps to nodes includes assigning a node the time at which it was last modified by an insertion or deletion of an element.
Claim 5
Dependent Claim
36 words
A method as claimed in Claim 2 and further characterized in that the step of assigning timestamps to nodes includes assigning a node the time at which it is split or deleted from the tree structure.
Claim 6
Dependent Claim
25 words
A method as claimed in Claim 1 and further characterized by the step of saving nodes of most recently read elements in a cache memory.
Claim 7
Dependent Claim
26 words
A method as claimed in Claim 1 and further characterized in that the step of obtaining a node containing the succeeding element using an associated pointer.
Claim 8
Dependent Claim
35 words
A method as claimed in Claim 6 and further characterized in that the step of obtaining the node containing the succeeding element includes locking the node so as to temporarily prevent it from being modified.
Claim 9
Dependent Claim
51 words
A method as claimed in Claim 1 and further characterized by the steps of: locking the last read part of the tree before comparing its current timestamp with the saved timestamp so as to temporarily prevent it from being modified; and unlocking the last read part after reading the succeeding element.
Claim 10
Dependent Claim
179 words
Apparatus for sequentially accessing and reading ordered elements of a data file while allowing the data file to be modified, the apparatus being characterized by: a first means (24) for storing the data file in the form of a tree structure (22) having ordered nodes, each node containing a subgroup of the ordered elements; a second means (30) for assigning timestamps to a node each time the node is modified or deleted by a respective operation; a third means (40) for storing an indication of an element which was last read and a timestamp corresponding to a node containing the element at a time of the reading of the elment; and means (26) for comparing the stored timestamp of the node to a current timestamp of the node just prior to reading a succeeding element of the last read element, the comparison means providing a search for a node currently containing the succeeding element if the current timestamp is different from the stored timestamp, and providing the succeeding element if the stored timestamp is equal to the current timestamp.
Claim 11
Dependent Claim
179 words
Apparatus for sequentially accessing and reading ordered elements of a data file while allowing the data file to be modified, the apparatus being characterized by: a first means (24) for storing the data file in the form of a tree structure (22) having ordered nodes, each node containing a subgroup of the ordered elements; a second means (30) for assigning timestamps to a node each time the node is modified or deleted by a respective operation; a third means (40) for storing an indication of an element which was last read and a timestamp corresponding to a node containing the element at a time of the reading of the elment; and means (26) for comparing the stored timestamp of the node to a current timestamp of the node just prior to reading a succeeding element of the last read element, the comparison means providing a search for a node currently containing the succeeding element if the current timestamp is different from the stored timestamp, and providing the succeeding element if the stored timestamp is equal to the current timestamp.
Claim 12
Dependent Claim
49 words
Apparatus as claimed in Claim 9 and further characterized in that a node is considered to be modified by an insertion or deletion of a element, and considered to be deleted by a splitting of the node elements into two nodes or deleting all the elements of the node.
References Cited (Backward Citations)
No citation records indexed.
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