What is the I/O cost of joining Attendees and Events tables using the index nested loops join algorithm?
The I/O cost of joining the Attendees and Events tables using the index nested loops join algorithm is approximately 108.8 page I/O.
Introduction to Index Nested Loops Join Algorithm
Index Nested Loops Join Algorithm involves using an index to access data from one table and then performing lookups in another table based on the matching values. In this case, a hash index on the "eveID" attribute of the Attendees table is utilized for the join.
Calculation of I/O Cost
Given that the Attendees table has 74 pages and the Events table has 20 pages, let's calculate the I/O cost step-by-step:
1. Search through Index in Attendees Table: For each of the 74 pages in the Attendees table, a search through the index using the hash index on "eveID" is performed. Since the cost of searching through the index is 1.2 page I/O, the total I/O cost for accessing all pages of the Attendees table is 74 * 1.2 = 88.8 page I/O.
2. Lookup in Events Table: For each matching record found in the Attendees table, a lookup is performed in the Events table. With the Events table having 20 pages, the total I/O cost for accessing all matching records in the Events table is 20 page I/O.
3. Total I/O Cost: By adding up the I/O costs from steps 1 and 2, the total I/O cost of joining the Attendees and Events tables using the index nested loops join algorithm is 88.8 page I/O (Attendees table) + 20 page I/O (Events table) = 108.8 page I/O.
It's important to recognize that this calculation is a simplification and actual I/O costs may vary due to factors like data distribution and the efficiency of index and disk operations.