Dynamic and Extendible Hashing in Database Systems

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Questions and Answers

What is the blocking factor (bfr) for a file?

  • The number of disk blocks allocated to hold the records of a file
  • The average number of file records stored in a disk block (correct)
  • The number of empty spaces in a block
  • The number of spanned records in a file

What does spanned records refer to in the context of file management?

  • Records with fixed-length format
  • Records that contain additional information like separator characters
  • Records stored in contiguous physical disk blocks
  • Records that exceed the size of one or more blocks and span multiple blocks (correct)

Which type of blocking is usually used with files of variable-length records?

  • Contiguous blocking
  • Linked blocking
  • Spanned blocking (correct)
  • Unspanned blocking

What information does a file descriptor include?

<p>Addresses of the file blocks on disk (D)</p> Signup and view all the answers

What happens when a new record hashes to a bucket that is already full in a hashed file system?

<p>An overflow file is used to store the new record (D)</p> Signup and view all the answers

In open addressing to resolve collisions, what does the program do?

<p>Checks subsequent positions until an empty position is found (D)</p> Signup and view all the answers

What additional field is added to each record location in chaining to handle collisions?

<p>Pointer field (D)</p> Signup and view all the answers

When multiple hashing is used, what happens if a collision occurs after applying a second hash function?

<p>A third hash function is applied (B)</p> Signup and view all the answers

What happens when an insertion in a disk block that is full occurs in dynamic hashing?

<p>The block splits into two blocks and the records are redistributed. (A)</p> Signup and view all the answers

What is the purpose of a directory in extendible hashing?

<p>To point to the disk blocks containing stored records. (B)</p> Signup and view all the answers

Which hashing technique does not require an overflow area?

<p>Dynamic hashing (B)</p> Signup and view all the answers

What is the difference between linear hashing and extendible hashing in terms of directory usage?

<p>Linear hashing does not use a directory, while extendible hashing does. (D)</p> Signup and view all the answers

What concept are organizations moving towards to achieve a more flexible and dynamic infrastructure for information processing?

<p>Storage Area Networks (SANs) (A)</p> Signup and view all the answers

What advantage do SANs provide in terms of connectivity among servers and storage devices?

<p>Many-to-many connectivity (C)</p> Signup and view all the answers

What is the maximum separation, in kilometers, that can be achieved between a server and a storage system in a SAN?

<p>10km (C)</p> Signup and view all the answers

What challenge do SANs face when it comes to dealing with storage options?

<p>Compatibility issues from multiple vendors (D)</p> Signup and view all the answers

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Study Notes

File Management

  • Blocking factor (bfr) for a file refers to the number of records in a block.
  • Spanned records refer to a single logical record that occupies multiple blocks on a disk.
  • Fixed-length blocking is usually used with files of fixed-length records, while variable-length blocking is used with files of variable-length records.

Hashed File System

  • When a new record hashes to a bucket that is already full in a hashed file system, overflow buckets are used to store the new record.
  • In open addressing, to resolve collisions, the program searches for the next available bucket in the table.
  • In chaining, an additional field is added to each record location to handle collisions, pointing to the next record in the chain.

Hashing Techniques

  • In multiple hashing, if a collision occurs after applying a second hash function, the process is repeated until an empty bucket is found.
  • In dynamic hashing, when an insertion occurs in a disk block that is full, the block is split into two blocks, and the keys are redistributed.

Extendible Hashing

  • The purpose of a directory in extendible hashing is to maintain a table of pointers to buckets on disk.
  • Extendible hashing does not require an overflow area.
  • The main difference between linear hashing and extendible hashing is that linear hashing uses a directory that grows linearly, while extendible hashing uses a directory that grows exponentially.

Storage Area Networks (SANs)

  • Organizations are moving towards achieving a more flexible and dynamic infrastructure for information processing using SANs.
  • SANs provide the advantage of connectivity among servers and storage devices, allowing multiple servers to access the same storage devices.
  • The maximum separation that can be achieved between a server and a storage system in a SAN is 10 kilometers.
  • SANs face the challenge of dealing with storage options, including compatibility and scalability issues.

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