Communications of the ACM
Communications of the ACM
Data Structure and Management
A compendium of key search references
ACM SIGIR Forum
Analysis of index-sequential files with overflow chaining
ACM Transactions on Database Systems (TODS)
A graduate course in database management
ACM SIGMOD Record
Hi-index | 48.22 |
The Index Sequential Access Method (ISAM) is one of the most important file management systems used with moveable head disk devices. This study investigates the use of an unconventional method of treating overflow records. The method is to use hashing techniques to allocate space for such records. If certain conditions are satisfied, this is superior to the conventional ISAM method of chaining the overflow records via linked list techniques. These conditions are: long overflow chains with significant overflow; lack of tight disk space constraints; record keys which are small compared to the total record size; and significant use of the file in the index as opposed to the sequential mode. Using hashed overflow, the time to locate a record is dependent not on the total volume of overflow records as in conventional ISAM, but on the percentage use of space dedicated to overflow records.