Complete unit 4

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 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