Please see attachment instructions to complete the assignment.
WK6 Discussion Instructions: Cost Functions and Record Lengths
250 words total, answer the questions below with 4 evidence base scholarly articles. APA format, due 15 Nov 24.
1. Discuss the different types of parameters that are used in cost functions. Where is this information kept?
2. What are the reasons for having variable-length records? What type of separator characters are needed for each? Illustrate with examples.
400 words total, replying to the two posts below. Each reply must be 200 words for post 1 and post 2.
Damien Post #1
Our text describes different types of parameters used in cost functions which include the size of each file, the number of tuples or records and their record size, the estimated number of file blocks, and potentially the blocking factor of the files. Additionally, the primary file organization should be considered either “unordered, ordered by an attribute with or without a primary or clustering index, or hashed (static hashing or one of the dynamic hashing methods) on a key attribute” (Elmasri, 2016). Per the referenced text, this information is stored in the Database Management System (DBMS) catalog for use by the query optimizer.
Elmasri describes four different reasons a file may have variable-length records. The first are if the file records are of the same type of record but with variable length fields such as the “Name” field of “Employee”. The file records may be the same record type but there may be multiple values for these records in a repeating field which can create a repeating group. One of the fields may be optional with values for only some of the fields, and lastly the file may contain records that are different record types which may create a mixed file. We’ve also learned that separator characters are required to terminate variable-length fields but are not meant to be included in the actual field value itself. These characters separate the data fields and may include symbols such as “?”, “%”, “$”, or “,” dependent on the type of file being utilized.
Elmasri, R., & Navathe, S. (2016). Fundamentals of Database Systems. Pearson.
Jennifer Post #2:
Hello Classmates,
· Discuss the different types of parameters that are used in cost functions. Where is this information kept?
According to text, a query optimizer estimates and compares the costs of executing a query using different execution strategies and algorithms to choose the strategy with the lowest cost estimate. The cost-based query optimization uses traditional optimization techniques that search the solution space to a problem for a solution that minimizes an object (cost) function. Cost functions are not exact cost functions providing estimates, which may lead to a query execution strategy that is not the best. Cost components for query execution include: access cost to secondary storage, disk storage cost, computation cost, memory usage cost, and communication cost. To keep track of the various execution strategies this information may be stored in the DBMS catalog, so it can be access by the query optimizer.
· What are the reasons for having variable-length records? What type of separator characters are needed for each? Illustrate with examples.
Reasons for having variable-length records include having different records with files of different sizes. Files have variable-length records for many reasons for example: containing more fields that vary in size, multiple values in a field, repeating fields, optional fields, and mixed file. They are useful in fields containing names, addresses, or descriptions, where the length of the data can differ. A separator character used such as ; , % or $ to separate one field from the next. For example separate customers information with semicolon (;) Lisa smith;123 Jason Ave;238-1234 or separation by commas(,) Victor Lee,1980 Bong Ave,648-1298.
Reference:
Elmasri, R., & Navathe, S. B. (2016). Fundamentals of database systems, 7th ed. New York, NY: Pearson Addison-Wesley.
