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Challenges in Database Record Modification: Insertion, Deletion, and Update Techniques

This comprehensive guide discusses the challenges faced during record modification in databases, specifically focusing on insertion, deletion, and update processes. For insertion, it addresses scenarios of sufficient and insufficient space within target blocks and introduces the concept of overflow blocks. Deletion techniques, including the use of tombstones, are also explored, along with methods to indicate deletions effectively. Additionally, the complexities of updating variable-length records are examined, presenting strategies for managing changes in record size, including sliding records and creating overflow blocks.

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Challenges in Database Record Modification: Insertion, Deletion, and Update Techniques

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  1. Database systemsthe complete book13.8. record modificationByAhmad Yazdankhah(ID 219)CS 257Prof.: T. Y. LinSan José State UniversitySPRING 2011

  2. Overview What problems we would have during: • Insertion • Deletion • Update

  3. 13.8.1. Insertion • What would we do for record insertion? • Find a block with enough empty space • Get a new block • But what would happen if we should insert the record in a specific block?

  4. 13.8.1. Insertion (cont’d) • There are two possibilities: • There is enough room in the target block • There is not enough room in the target block • In the 1st case, insert and update the offset table • In the 2nd case, there are two approaches: • Find space on a nearby block and slide the records • Create an overflow block

  5. 13.8.1. Insertion (cont’d) • What is an overflow block? • It is another block in which we put the records that theoretically belong to this block. • In block’s header, there is a pointer to an overflow.

  6. 13.8.2. Deletion • The usual technique is to put a tombstone in place of the record. • This is not the case that we delete the record physically. • This is a permanent tombstone until the database is reconstructed.

  7. 13.8.2. Deletion (cont’d) • Where to put the sign of deletion? • If using offset table in the block header, put null in the pointer’s place • If using a map table, put null in physical address

  8. 13.8.3. Update • No problem if fixed length records • The problems arise for variable length records • We have all problems mentioned for insertion and deletion

  9. 13.8.3. Update (cont’d) • If the new record is shorter: • Slide down the records to consolidate the free spaces • If the new record is longer: • Slide down the records to make room • Create an overflow block

  10. Thank You

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