Physical Database Design Assignment: Query Optimisation
This assignment aims to develop your skills optimizing query.
It involves identifying the suitable methods for structuring the data and writing the query.
First, you will need to create a query on some unstructured data. Unstructured data can be thought of in this context as a table which is NOT clustered or hashed. In addition the table should NOT contain any indexes at all. The query can be an equi-join or a sub-query.
The time a query with unstructured data takes to execute (execution time) will be used as the baseline.
Plan how to set up indexes, clusters, and hashed clusters for the same query. Use different numbers of rows and graph these for each type of structure. You need to create enough rows to indicate a trend in the performance (Number of rows should be enough).
You should then run the query and note the execution times for EACH of these structures.
Record the results. When doing this you could alter the way you set up some of these structures by, for instance, altering the hashkey or what you cluster together and note any differences in execution time.
You should by now have determined the optimal data structure in terms of performance. To be confident that your data will make things difficult for Oracle, ensure that:
- the data is as unordered as possible
- you retrieve a number of rows
You now have some choices about how you might improve the SQL statement. Take the best optimisation and try to improve it by inserting hints and swapping the order of the tables in the 'from' clause of your query.
The best of these 'improved' statements then needs to be tried out using Oracle's Parallel Query Option.
