Replacement in the Background

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3.3 Replacement in the Background

Although our replacement overhead is low, we also have designed the system to allow replacement to be done in the background. HAC always maintains a free frame, which is used to store the incoming page. Another frame must be freed before the next fetch, which can be done while the client waits for the fetch response.

3.4 Summary

The client maintains usage information for each object to differentiate between hot and cold objects. It periodically scans frames in the cache, computes summary usage values for these frames, and enters this information in the candidate set. The candidate set maintains the summary usage information of frames that have been scanned during the last few fetches. When a cache miss occurs, the client fetches the missing page into a free frame, and frees a new frame for the next fetch by compacting the least valuable frames from the candidate set: it copies their hot objects into the current target frame and evicts their cold objects.

Miguel Castro, Atul Adya, Barbara Liskov, and Andrew Myers

Copyright ©1997 by the Association for Computing Machinery