13 8 record modifications
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13.8 Record Modifications. CS257 Lok Kei Leong ( 108 ). Outline. Record Insertion Record Deletion Record Update. Insertion. Insert new records into a relation - records of a relation in no particular order - record of a relation in fixed order (e.g. sorted by primary key)

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13.8 Record Modifications

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13 8 record modifications

13.8 Record Modifications

CS257

Lok Kei Leong ( 108 )


Outline

Outline

  • Record Insertion

  • Record Deletion

  • Record Update


Insertion

Insertion

  • Insert new records into a relation- records of a relation in no particular order- record of a relation in fixed order (e.g. sorted by primary key)

  • A pointer to a record from outside the block is a “structured address”

Offeset table

header

unused

Record 2

Record 3

Record 4

Record 1


What if the block is full

What If The Block is Full?

  • If we need to insert the record in a particular block but the block is full. What should we do?

  • Find room outside the Block

  • There are 2 solutions

  • Find Space on Nearby Block

  • Create an Overflow Block


Insertion solution 1

Insertion (solution 1)

  • Find space on a “nearby” block

  • Block B1 has no space

  • If space available on block B2 move records of B1 to B2

  • If there are external pointers to records of B1 moved to B2 leave forwarding address in offset table of B1


Insertion solution 2

Insertion (solution 2)

  • Create an overflow block

  • Each block B has its header pointer to an overflow block where additional blocks of B can be placed

Block B

Overflow block for B


Deletion

Deletion

  • Slide around the block

  • Cannot slide records- maintain an available-space list in the block headerto keep track of space available

  • Avoid dangle or wind up pointing to a new record


Tombstone

Tombstone

  • What about pointer to deleted records ?

  • A tombstone is placed in place of each deleted record

  • A tombstone is a bit placed at first byte of deleted record to indicate the record was deleted ( 0 – Not Deleted 1 – Deleted)

  • A tombstone is permanent

Record 1

Record 2


Update

Update

  • For Fixed-Length Records, there is no effect on the storage system

  • For variable length records:

  • associated with insertion and deletion(never create a tombstone for old record)

  • Longer updated recordcreate more space on its block- sliding records - create an overflow block


Question

Question?


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