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8-Storage Structure

8-Storage Structure - Storage Structure Presenter Tathagata...

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Storage Structure Tathagata Bhattacharjee Storage Structure Presenter Tathagata Bhattacharjee
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Storage Structure Tathagata Bhattacharjee Objectives After completing this lesson, you should be able to do the following: – Describe the logical structure of the database – List the segment types and their uses – List the keywords that control block space usage – Obtain information about storage structures from the data dictionary – List the criteria for separating segments
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Storage Structure Tathagata Bhattacharjee OVERVIEW Database Tablespace Segment Extent Oracle Block Datafile OS Block L O G I C A L P H Y S I C A L
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Storage Structure Tathagata Bhattacharjee Types of Segments 1. Table 2. Partitioned table 3. Cluster 4. Index 5. Index organized table 6. Index partition 7. Undo segment 8. Temporary segment 9. LOB segment 10.Nested table 11.Bootstrap segment
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Storage Structure Tathagata Bhattacharjee Table A table is a most common means of storing data within a database A table segment stores that data for a table that is neither clustered nor partitioned Data within a table segment is stored in no particular order and the DBA has very little control over the location of rows within the blocks in a table All the data in a table segment must be stored in one tablespace
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Storage Structure Tathagata Bhattacharjee Table Partition Scalability and availability are major concerns where there is a table in a database with high concurrent usage In such cases, data within a table may be stored in several partitions, each of which resides in a different tablespace. Oracle server currently supports partitioning by a range of key values or by a hashing algorithm. If a table is partitioned, each partition is a segment, and storage parameters can be specified to control them independently.
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Storage Structure Tathagata Bhattacharjee Cluster A cluster, like a table, is a type of data segment. Rows in a cluster are stored based on key column values A cluster may contain one or more tables Tables in a cluster belong to the same segment and share the same storage characteristics The rows in a clustered table can be accessed with an index or hashing algorithm
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Storage Structure Tathagata Bhattacharjee Index • All the entries for a particular index are stored within one index segment. • If a table has three indexes, three index segments are used • The purpose of this segment is to look up the location of rows in a table based on a specific key
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Storage Structure Tathagata Bhattacharjee Index-Organized Table • In an index-organized table, data is stored within the index based on the key value. • An index-organized table does not need a table lookup, because all the data can be retrieved directly from the index tree
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Storage Structure Tathagata Bhattacharjee Index Partition • An index can be partitioned and spread across several tablespaces.
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