Suppose we are given a database with the following schema. Users User IDINTEGER,

Question

Suppose we are given a database with the following schema. Users User IDINTEGER, Name CHAR(30), Age INTEGER, ReviewCount INTEGER) Businesses (BusinessID INTEGER, BName CHAR(30), City CHAR(20), State CHAR(2) Checkins (BusinessIDINTEGER, Weekdays INTEGER, Weekends INTEGER) Reviews (ReviewID INTEGER, UserIDINTEGER, BusinessID INTEGER, Stars REAL) Reviews (UserID) is a foreign key referring to Users (UserID). Reviews (BusinessID) is a foreign key referring to Businesses (BusinessID). Checkins (BusinessID) is a foreign key referring to Businesses (BusinessID) A page is 8 kB in size. The RDBMS buffer pool has 10,000 pages, all of which are usable. Initially, the buffer pool is empty. The relation instances have the following statistics. Assume there are no NULL values. Each integer or real is 8B, and each character is 1B (so as an example CHAR(20) is 20B). Additionally, the record id of each tuple is 8B. Relation Number of Pages Number of Tuples 75,684 10m. Users 41,504 5mm Businesses 19,532 5mm Checkins Reviews 488,282 100m

Explanation / Answer

Answer

Each entry in the hash table will be of size = 20B + 8B = 28B (i.e. 20B for the key, and 8B for the count, which is an integer).

If C is the number of cities, the size of the hash table (in pages) will be

f × C × 28/(8 × 1024)

This must fit in the (B 1) available buffer pages.

Thus, we have C 8 × 1024 × (B 1)/(28 × f)

which means C 2, 089, 586

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