CSCD43 DATABASE SYSTEM TECHNOLOGY数据库系统作业代写 In this assignment, you will carry out a number of experiments involving the optimization of queries using the PostgreSQL query optimizer.Due Friday April 9 Weight: 15% of your ftnal gradeAssignment 3Query Optimization1 Outline 数据库系统作业代写In this assignment, you will carry out a number of experiments involving the optimization of queries using the PostgreSQL query optimizer. The primary focus will be on statistics collected and used by the PostgreSQL query optimizer.2 Setup 数据库系统作业代写Download the files csv andtwo.csv fromhttp://www.cs.toronto.edu/~koudas/courses/cscd43/one.csv http://www.cs.toronto.edu/~koudas/courses/cscd43/two.csvThe tables corresponding to these files can be created by the following SQL statements.CREATE TABLE One(id integer, b  integer, c  integer, d integer);CREATE TABLE Two(id integer, a integer);Load the csv files into the database using the copy command of psql. Create indices on each of the attributes in the database, using the CreateIndex command.Runthe vacuum analyze command to update the statistics on the tables.数据库系统作业代写Run a few sample queries to get an idea of the ranges and data distributions on each of the attributes.3 Evaluation 数据库系统作业代写3.1 System CatalogsEach time you run vacuum analyze on PostgreSQL , the system catalogs are updated. The extent of statistics collection is controlled by a variable default_statistics_target that can take values between 0and 1000, with the default value of 10. This variable can be changed using the set command of psql. Eachtime you change the value of this variable, you should run vacuum  analyze to update the statistics.PostgreSQL collects a wide variety of statistics about each attribute.  The most important ones  are:the most common values (MCVs) and their frequencies,andaset of bucket boundaries for an equi-width   数据库系统作业代写This statistical information can be easily accessed by simple SQL queries on the PostgreSQL system catalogs. The system catalogs of PostgreSQL are well documented and the statistical information can be easily found with a casual websearch.数据库系统作业代写Answer the following questions.Usethe PostgreSQL catalog to find the number of distinct values of each of the attributes in table One. Write the SQL query you used to find out this information.Use the catalog to find out the space used by the relation Two on the disk, in number of bytes. Write downthe SQL query used to find this information.数据库系统作业代写3.2 Equality QueriesConsider a set (with size at least two) of equality queries of the formSELECT * FROM One WHERE d = value;Set value to a high-frequency value of the attribute d.  Which query plan is selected by  PostgreSQL toexecute this query? (This information can be found by using the explain command).数据库系统作业代写Setvalue to a low-frequency value of the attribute d. Which query plan is selected by PostgreSQL to execute this query now?If the two query plans (corresponding to the two cases) are different, try to find the cross-over point  interms of frequency, e., the pointabovewhich one plan is used, andbelow which the other plan is Why does such a cross-over point exist?

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