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diff --git a/doc/unit-4.md b/doc/unit-4.md index 436acd6..2a159ac 100644 --- a/doc/unit-4.md +++ b/doc/unit-4.md @@ -332,3 +332,24 @@ Guidelines: 7. If the key for the index is used to determine the location where the record will be stored then a surrogate key should be used. 8. Check DBMS for limits on the # of indexes on a table. (limits include # of indexes, and size of index) 9. Be careful indexes attributes that have null values. some systems don't index `null` so sequential scan is needed for `null` value. + +### Designing a database for optimal query performance + +Primary purpose of database design is to optimize the performance of database processing. + +Parallel query processing + +## Summary + +denormalization transforms normalized relations into non-normalized implementations specs. +Horizontal paritioning breaks a relation into multiple record specifications by placing different +rows into different tables, based on common column values. +Vertical partitioning distributes the columns of a relation into separate files, repeating the primary key in each of the files. + +A physical file is a named portion of secondary memory for storing physical records. + +A file organization arranges the records of a file on a secondary storage. + +1. sequential +2. indexed (most popular) +3. hashed |