8-Storage Structure

Bsq script when a database is created this segment

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Unformatted text preview: known as a cache segment, is created by sql.bsq script when a database is created. • This segment helps to initialize the data dictionary cache when the database is opened by an instance • The bootstrap segment cannot be queried or updated and does not require any maintenance by the database administrator Bootstrap Segment Storage Structure – Dropped – Altered – Truncated Tathagata Bhattacharjee • Deallocated when the segment is – Created – Extended – Altered • Allocated when the segment is Extent Allocation and Deallocation Storage Structure Tathagata Bhattacharjee • When a tablespace is created, the data files in the tablespace contain a header, which is the first block or blocks in the file • As segments are created, they are allocated space from the free extents in a tablespace • Contiguous space used by a segment is referred to as used extent • When segments release space, the extents that are released are added to the pool of free extents available in the tablespace Used and Free Extents Storage Structure Tathagata Bhattacharjee • Minimum unit of I/O • Consists of one or more OS blocks • Set at tablespace creation • DB_BLOCK_SIZE is the default block size Database Block Storage Structure Tathagata Bhattacharjee • Block Header: The header contains the data block address, table directory, row directory and transaction slots that are used when transactions make changes to rows in the block. Block headers grow from top down • Data Space: Row data is inserted into the block from the bottom up Database Block Contents Storage Structure Tathagata Bhattacharjee • Free Space: The free space in a block is in the middle of the block: thus both the header and the row data space can grow when necessary. The free space in a block is contiguous initially. However, deletion and updates may fragment the free space in the block. The free space in the block is coalesced by the Oracle server when necessary Storage Structure Tathagata Bhat...
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This note was uploaded on 07/15/2011 for the course ECO 2023 taught by Professor Mr.raza during the Summer '10 term at FAU.

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