Database-Management-System
August 29, 2024Database-Management-System
August 29, 2024Database-Management-System
|
Question 349
|
B+ –tree are preferred to binary trees in databases because
|
Disk capacities are greater than memory capacities
|
|
|
Disk access is much slower than memory access
|
|
|
Disk data transfer rates are much less than memory data transfer rates
|
|
|
Disks are more reliable than memory
|
Question 349 Explanation:
The major advantage of the B+ tree (and B-trees in general) over binary search trees is that they play well with caches. If you have a binary search tree whose nodes are stored in more or less random order in memory, then each time you follow a pointer, the machine will have to pull in a new block of memory into the processor cache, which is dramatically slower than accessing memory already in cache.
The B+-tree and the B-tree work by having each node store a huge number of keys or values and have a large number of children. They are typically packed together in a way that makes it possible for a single node to fit nicely into cache (or, if stored on disk, to be pulled from the disk in a single read operation). You then have to do more work to find a key within the node or determine which child to read next, but because all memory accesses done on a single node can be done without going back to disk, the access times are very small. This means that even though in principle a BST might be better in terms of number of memory accesses, the B+-tree and the B-tree can perform better in terms of the runtime of those memory accesses.
The B+-tree and the B-tree work by having each node store a huge number of keys or values and have a large number of children. They are typically packed together in a way that makes it possible for a single node to fit nicely into cache (or, if stored on disk, to be pulled from the disk in a single read operation). You then have to do more work to find a key within the node or determine which child to read next, but because all memory accesses done on a single node can be done without going back to disk, the access times are very small. This means that even though in principle a BST might be better in terms of number of memory accesses, the B+-tree and the B-tree can perform better in terms of the runtime of those memory accesses.
Correct Answer: B
Question 349 Explanation:
The major advantage of the B+ tree (and B-trees in general) over binary search trees is that they play well with caches. If you have a binary search tree whose nodes are stored in more or less random order in memory, then each time you follow a pointer, the machine will have to pull in a new block of memory into the processor cache, which is dramatically slower than accessing memory already in cache.
The B+-tree and the B-tree work by having each node store a huge number of keys or values and have a large number of children. They are typically packed together in a way that makes it possible for a single node to fit nicely into cache (or, if stored on disk, to be pulled from the disk in a single read operation). You then have to do more work to find a key within the node or determine which child to read next, but because all memory accesses done on a single node can be done without going back to disk, the access times are very small. This means that even though in principle a BST might be better in terms of number of memory accesses, the B+-tree and the B-tree can perform better in terms of the runtime of those memory accesses.
The B+-tree and the B-tree work by having each node store a huge number of keys or values and have a large number of children. They are typically packed together in a way that makes it possible for a single node to fit nicely into cache (or, if stored on disk, to be pulled from the disk in a single read operation). You then have to do more work to find a key within the node or determine which child to read next, but because all memory accesses done on a single node can be done without going back to disk, the access times are very small. This means that even though in principle a BST might be better in terms of number of memory accesses, the B+-tree and the B-tree can perform better in terms of the runtime of those memory accesses.