Module 8

Under what circumstances must a database index be updated? -A record is updated in the database. -A security key is added to the database. -A record is deleted from the database. -A record is inserted into a databse.

-A record is deleted from the database. -A record is inserted into a databse.

Which of the following are true about B+ tree index files? -Each node contains d -Insert / delete at logFN cost where F = fanout and N = # leaf pages. -Maximum 50% occupancy (except for root). -Each node contains exactly 2d entries. d is called the order of the tree. -B+ tree is the most widely used index.

-Each node contains d -Insert / delete at logFN cost where F = fanout and N = # leaf pages. -B+ tree is the most widely used index.

When choosing a hash function to assign search key values to buckets, the function should have which of the following qualities? -Normalized distribution. -Exponential distribution. -Random distribution. -Uniform distribution. -Linear distribution.

-Random distribution. -Uniform distribution.

Which of the following are true about B+ tree-based indexing? -Finding the correct leaf page is done in nlogn time, where time is measured by node accesses. -The lowest level of the tree - called the leaf level - contains the data entries. -The data is contained within the nodes as well as in the leafs. -Finding the correct leaf page is faster than a binary search. -It is an index structure that ensures that all paths from the root to a leaf in a given tree are of the same height.

-The lowest level of the tree - called the leaf level - contains the data entries. -Finding the correct leaf page is faster than a binary search. -It is an index structure that ensures that all paths from the root to a leaf in a given tree are of the same height.

For a set of 100 data records with 5 fields per record, how many clustered indexes can there be?

1

Match the operation while deleting a data entry from a B+ tree to its order of sequence. 1. Find Leaf L where entry exists. 2. Remove entry, replace index if necessary 3. If L falls below d, try to redistribute 4. If L falls below d and redistribution fails, merge L with sibling 5. Recursively merge index nodes where necessary.

1. Find Leaf L where entry exists. 2. Remove entry, replace index if necessary 3. If L falls below d, try to redistribute 4. If L falls below d and redistribution fails, merge L with sibling 5. Recursively merge index nodes where necessary.

Match the steps to insert a data entry into a B+ tree to their order.

1. Find the correct leaf L 2. If room in L, put data entry into L; done 3. Split L, redistribute entries evenly, copy up middle key 4. Insert index entry pointing to L2 into parent of L 5. If necessary, split index node recursively.

A B+ tree with a typical order of 100 and fill factor of 2/3 (i.e. fanout of 133), with a height of 4 can handle how many records?

133^4

The primary difference between a B tree indices and a B+ tree indices is which of the following?

A B-tree eliminates the redundant storage of search-key values.

When a file is organized so that the ordering of data records is the same as or close to the ordering of data entries in some index, we say that is:

A clustered index.

Which of the following is true about primary and secondary indexes?

A primary index is one that does not allow duplicates, a secondary index is one that does.

The time it takes for a particular hashing or indexing technique to find a particular data item, or set of items.

Access time

Static hashing is done by performing which of the following?

Applying a hash function h to the search key to identify the bucket to which it belongs and then searching this bucket.

The time it takes for a particular hashing or indexing technique to delete a data item.

Deletion time

The key attribute of a hashing function is which of the following?

Even distribution of the entries throughout the table.

A primary index is one that includes the primary key, indexes that include only other candidate keys are called secondary indexes. (T/F)

False

A search key is the same as a candidate key. (T/F)

False

The ability to double the directory by simply copying the directory to the lower part is accomplished because we are using the most significant bits. (T/F)

False

An indexing technique based on a uniform distribution of values across a range of buckets.

Hash index

A global depth indicator N in an extendible hashing scheme is used to identify which of the following?

Identifies that there are 2**N number of entries in the directory.

The time it takes for a particular hashing or indexing technique to insert a new data item.

Insertion time

An indexing technique based on a sorted ordering of the values.

Ordered index

The key advantage of using a B+ tree for an index file as opposed to a hashing scheme is which of the following?

Range searches

Any attribute or set of attributes with which a file may locate a record or set of records.

Search key

When some hash buckets are assigned more records than are others, and a bucket may overflow even as other buckets still have space, it is called ________________.

Skew

The additional space occupied by an index structure for a particular hashing or indexing technique.

Space overhead

Which of the following best describes the advantage of hashing over a tree structure for indexing ?

Storing indexes in hash structures could result in less disk I/Os.

Which of the following is true about tree-structured indexing techniques?

Support both range searches and equality searches.

Both the global and the local depth use the value to identify which of the following?

The number of bits of the value returned from the hash table to use.

In an extendible hashing scheme, the directory structure is grown when which of the following is true?

The size of the local depth indicatory exceeds the global indicator after the insert.

A range search is the concept of finding all records where the seach key value is less than some value and/or greater than another value. (T/F)

True

Extendible hashing schemes solve the problems of a static hash scheme by implementing a directory of pointers to buckets and growing the directory appropriately. (T/F)

True

One of the problems with a static hashing scheme is that long overflow chains develop. (T/F)

True

A B+ tree index takes the form of a ______________ tree in which every path from the root of the tree to a leaf of the tree is of the same length.

balanced