Slideshow:
How to lookup using a
Grid Index file
Find the data record with search key (Age = 50, Salary = 100)
Found: row index = 1
How to lookup using a
Grid Index file
Find the data record with search key (Age = 50, Salary = 100)
Found: column index = 1
How to lookup using a
Grid Index file
Find the data record with search key (Age = 50, Salary = 100)
Use this offset to access the index entry:
Inserting a new index into a Grid Index file
Performance of the Grid Index
Performance of the Grid Index
Performance of the Grid Index
- Given: search key
(Age = 50, Salary = 100)
How to find this record:
- Find the row index using
age = 50:
- Find the column index using
salary = 100:
- Find the offset
(this is the standard way to
find an array element):
offset = row index * (column width) + column index = 1 * 3 + 1 = 4
- Access the blocks
and search for the record:
- Find the row index using
age = 50:
- Insert:
insert( recordSearchKey, recordPtr ) { B = Lookup( recordSearchKey ); Let b = the last bucket block in the chain B; if ( b has room for record ) { Insert recordSearchKey, recordPtr in block b; } else { Allocate an overflow block for bucket; Link overflow block to b Insert recordSearchKey, recordPtr in overflow bucket block; } }
- Assumption:
- The grid index file can be store in memory
- Lookup performance:
- 0 block access to obtain
the bucket block pointer
- 1 block access to obtain the
data block
(that contains the record)
(If there are overflow blocks, we need to access a few more (overflow) blocks)
- 0 block access to obtain
the bucket block pointer
- Insert performance:
- In addition to
the lookup cost:
- 1 more block write
operation to
update the
bucket block
(If overflow, we need to update the overflow link in the bucket and write an overflow block)
- 1 more block write
operation to
update the
bucket block
- In addition to
the lookup cost: