Discussion
In a file that uses hash-based organization, overflow chains degrade performance mainly due to which of the following ?
Answer: A
Overflow chains degrade performance mainly through increased seek time.
In a hashed file, a record's key leads straight to one bucket, ideally one block read. When a bucket fills up, further records go into overflow blocks chained from it. Finding a record may then mean reading the bucket and following the chain block by block, and overflow blocks are usually stored elsewhere on the disk, so each extra block costs another head movement. As chains grow, a lookup that should take one access takes several.
Bucket alignment is not the issue. Hashed files never kept alphabetical order, so nothing is lost there. Rotational latency is incurred with each access too, but the dominant extra cost is the seek to each scattered overflow block.
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