Presentation on   tablespacessegments extends    and blocks
CONTENT   Introduction.   what are blocks?   what are extends?   what are segments?   what are tablespaces?
INTRODUCTION Oracle allocates logical database space for all data in a database. The units of database space allocation ...
BLOCKS Data Blocks is smallest logical unit to store  Oracle Data. One data block represent specific number of  bytes on...
Format of data block is
  Header : contains generic information like  block address and type of segment (index,  data.) Table Directory : contai...
EXTENDS Extent is collection of contiguous data  blocks. One or more extents make up a segment. When the existing space...
When Extents Are              Allocated When you create a table, Oracle allocates to the tables  data segment an initial ...
SEGMENTS Segment is set of extents allocated for  specific data structure (like table or  index). Various kind of segmen...
Things to note w.r.t. Segment,     Extent & Datablocks Segment and its associated extents are stored  in one table space....
The Relationships Among Segments,    Extents, and Data Blocks  •
TABLESPACES Tablespaces are the bridge between  certain physical and logical components of  the Oracle database. Tablespa...
PRESENTED BY :• VINAY UGAVE (SDBCT,INDORE)               SUBMITTED TO:               MISS GARIMA JOSHI
Presentation on tablespaceses segments extends and blocks
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Presentation on tablespaceses segments extends and blocks

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According to RGPV syllabus ,BHOPAL

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Presentation on tablespaceses segments extends and blocks

  1. 1. Presentation on tablespacessegments extends and blocks
  2. 2. CONTENT Introduction. what are blocks? what are extends? what are segments? what are tablespaces?
  3. 3. INTRODUCTION Oracle allocates logical database space for all data in a database. The units of database space allocation are data blocks, extents, and segments.  Oracle stores data logically in tablespaces and physically in datafiles associated with the corresponding tablespace.
  4. 4. BLOCKS Data Blocks is smallest logical unit to store Oracle Data. One data block represent specific number of bytes on physical hard disk. Data Block size is usually multiple of operating system block size  You can have multiple block sizes with in single database (max. five).  Block Size is specified by initialization parameter DB_BLOCK_SIZE Data Block in Oracle is also called as logical block
  5. 5. Format of data block is
  6. 6.   Header : contains generic information like block address and type of segment (index, data.) Table Directory : contains information about table having rows in that block Row Directory : contains information about actual row contained in that block Free Space : available space in data block for additional row or update of row which require more space. Row Data : contains table or index data.First three component of data block (Header, Table & Row directory) collectively known as Overhead
  7. 7. EXTENDS Extent is collection of contiguous data blocks. One or more extents make up a segment. When the existing space in a segment is completely used, Oracle allocates a new extent for the segment.
  8. 8. When Extents Are Allocated When you create a table, Oracle allocates to the tables data segment an initial extent of a specified number of data blocks. Although no rows have been inserted yet, the Oracle data blocks that correspond to the initial extent are reserved for that tables rows. If the data blocks of a segments initial extent become full and more space is required to hold new data, Oracle automatically allocates an incremental extent for that segment. An incremental extent is a subsequent extent of the same or greater size than the previously allocated extent in that segment. For maintenance purposes, the header block of each segment contains a directory of the extents in that segment.
  9. 9. SEGMENTS Segment is set of extents allocated for specific data structure (like table or index). Various kind of segments are table, index, cluster, rollback, temporary … Important views for segments are dba_segments, user_segments,all_se gments In a Segment, first block of first extent contains segment header information
  10. 10. Things to note w.r.t. Segment, Extent & Datablocks Segment and its associated extents are stored in one table space. Extents of a segment may not be contiguous on disk Segment can span multiple datafiles of a particular tablespace (Information on tablespace & datafiles coming soon) but extent can contain data from only one datafile.
  11. 11. The Relationships Among Segments, Extents, and Data Blocks •
  12. 12. TABLESPACES Tablespaces are the bridge between certain physical and logical components of the Oracle database. Tablespaces are where you store Oracle database objects such as tables, indexes and rollback segments.  You can think of a tablespace like a shared disk drive in Windows. You can store files on your shared drive, move files around and remove files. The same is true with tablespaces. 
  13. 13. PRESENTED BY :• VINAY UGAVE (SDBCT,INDORE) SUBMITTED TO: MISS GARIMA JOSHI

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