Understanding Sequential Flooding in Database Management Systems

Which of the following is FALSE regarding "sequential flooding"?

Group of answer choices

a. The LRU replacement policy is susceptible to sequential flooding.

b. The sequential flooding pollutes the buffer pool with pages that are read once and then never again.

c. The sequential flooding is caused by a query performs a sequential scan that reads every page.

d. The CLOCK replacement policy is immune from the sequential flooding.

The FALSE statement regarding "sequential flooding" is option d. The CLOCK replacement policy is not immune from sequential flooding. Sequential flooding refers to a situation where a query performs a sequential scan, reading every page and filling up the buffer pool with pages that are read once and then never again. Both the LRU (Least Recently Used) and CLOCK replacement policies are susceptible to sequential flooding, as they may retain these one-time accessed pages in the buffer pool, potentially evicting more useful pages from the pool. Therefore, option d is incorrect.

Understanding Sequential Flooding

Sequential flooding is a phenomenon in database management systems where a query performs a sequential scan, reading each page in order. This can lead to the buffer pool getting filled with pages that are only read once and then never accessed again. The term "sequential flooding" comes from the idea that the pages flood the buffer pool in a sequential manner, filling it up with potentially unnecessary data.

LRU Replacement Policy and Sequential Flooding

The LRU (Least Recently Used) replacement policy is one of the commonly used algorithms to manage buffer pools in database systems. However, this policy is susceptible to sequential flooding. When a query performs a sequential scan and fills up the buffer pool with pages that are read once and then never again, the LRU replacement policy might retain these pages, leading to less efficient memory usage.

CLOCK Replacement Policy and Sequential Flooding

The CLOCK replacement policy is another popular algorithm used for managing buffer pools. While it is often considered more efficient than LRU in certain scenarios, it is not immune from sequential flooding. Just like the LRU policy, the CLOCK policy can also retain one-time accessed pages in the buffer pool, potentially causing the eviction of more useful pages.

Impact of Sequential Flooding

Sequential flooding can have a negative impact on the performance of a database management system. When the buffer pool is filled with pages that are only accessed once, it can lead to inefficiencies in memory usage and slower query performance. It is crucial for database administrators to monitor and optimize the buffer pool to prevent sequential flooding and ensure optimal performance.

Conclusion

In conclusion, option d stating that the CLOCK replacement policy is immune from sequential flooding is incorrect. Both the LRU and CLOCK replacement policies are susceptible to sequential flooding, where one-time accessed pages can fill up the buffer pool and impact the efficiency of the database system. It is essential for database administrators to understand the concept of sequential flooding and employ strategies to mitigate its effects for better system performance.