{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Data Mgmt Lab_Part_41 - Overview of Query Evaluation 121 2...

Info icon This preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Overview of Query Evaluation 121 2. An access path is a way of retrieving tuples from a table and consists of either a file scan or an index plus a matching selection condition. An index matches a selection condition if the index can be used to retrieve just the tuples that satisfy the condition. An index can match some subset of conjunts in a selection condition even though it does not match the entire condition and we refer to the conjuct that the index matches as the primary conjuncts in the selection. Primary conjuncts are important because they allow us to quickly discard information we do not need and only focus in on searching/sorting the data that more closely matches the selection conditions. 3. Information about relations, indexes, and views is stored in the system catalogs. This includes file names, file sizes, and file structure, the attribute names and data types, lists of keys, and constraints. Some commonly stored statistical information includes: (a) Cardinality - the number of tuples for each relation (b) Size - the number of pages in each relation (c) Index Cardinality - the number of distinct key values for each index (d) Index Size - the number of pages for each index (or number of leaf pages) (e) Index Height - the number of nonleaf levels for each tree index (f) Index Range - the minimum present key value and the maximum present key value for each index.
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern