| 摘要 |
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. |
