File Storage and Indexing
File Storage and
Indexing
Lesson 13 CS 3200 Kathleen Durant PhD
1
Today's Topics
? Overview of data flow: External storage to RAM ? File organizations available
? Effects on DBMS performance
? Introduction to indexes
? Clustered vs. Unclustered
? Model for evaluating the cost of DB operations for the different file organizations
? Methods available for improving system performance
? Indexes and when to use them or not to use them (while evaluating a query)
2
What topics have we covered so far?
SQL
Interface
Properties of DBMS
Glossed over Translating transactions to database actions
Transactions Page buffer Recovery
3
Where can you store a database?
? Disks: Can retrieve random page at fixed cost
? But reading several consecutive pages is much cheaper than reading them in random order
? Tapes: Can only read pages in sequence
? Cheaper than disks; used for archival storage
? Flash memory: Starting to replace disks due to much faster random access
? Writes still slow, size often too small for DB applications
? Arrays of disks
? Cover in later chapter
4
Why care about the data storage mechanism?
? DB performance depends on the time it takes to get the data from the storage system
? I/O operations are slow
? It's all about expectations
? If you are reading lots of data then it's OK to take a while ? If you are reading a small amount of data it should be quick
Goal: store the data in an order that
will make it easy to find / identify a
particular record(s)
5
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