Class: PEROBS::BigHash

Inherits:
Object show all
Defined in:
lib/perobs/BigHash.rb

Overview

The BigHash is similar to the Hash object in that it provides a simple hash functionality. The difference is that this class scales to much larger data sets essentially limited to the amount of space available on your backing store. The data is persisted immediately and uses transactions to ensure the data consistent. It only provides a small subset of the methods provided by the native Hash class that make sense for giant data sets.

Defined Under Namespace

Classes: Collisions, Entry

Constant Summary

Constants inherited from ObjectBase

ObjectBase::NATIVE_CLASSES

Instance Attribute Summary

Attributes inherited from Object

#attributes

Attributes inherited from ObjectBase

#_id, #myself, #store

Instance Method Summary collapse

Methods inherited from Object

#_delete_reference_to_id, #_deserialize, #_referenced_object_ids, #attr_init, attr_persist, #init_attr, #inspect, #mark_as_modified

Methods inherited from ObjectBase

#==, #_check_assignment_value, _finalize, #_initialize, #_restore, #_stash, #_sync, #_transfer, read

Constructor Details

#initialize(p) ⇒ BigHash

Create a new BigHash object.

Parameters:



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# File 'lib/perobs/BigHash.rb', line 71

def initialize(p)
  super(p)
  restore
  self.btree = @store.new(PEROBS::BigTree)
end

Instance Method Details

#[](key) ⇒ Any PEROBS storable object

Retrieve the value for the given key. If no value for the key is found nil is returned.

Parameters:

  • key (Integer or String)

Returns:

  • (Any PEROBS storable object) 


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# File 'lib/perobs/BigHash.rb', line 127

def [](key)
  hashed_key = hash_key(key)
  unless (entry = @btree.get(hashed_key))
    return nil
  end

  if entry.is_a?(PEROBS::Array)
    entry.each do |ae|
      return ae.value if ae.key == key
    end
  elsif entry.key == key
    return entry.value
  end

  nil
end

#[]=(key, value) ⇒ Object

Insert a value that is associated with the given key. If a value for this key already exists, the value will be overwritten with the newly provided value.

Parameters:

  • key (Integer or String)
  • value (Any PEROBS storable object) 


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# File 'lib/perobs/BigHash.rb', line 84

def []=(key, value)
  hashed_key = hash_key(key)
  @store.transaction do
    entry = @store.new(Entry, key, value)

    if (existing_entry = @btree.get(hashed_key))
      # There is already an existing entry for this hashed key.
      if existing_entry.is_a?(Collisions)
        # Find the right index to insert the new entry. If there is
        # already an entry with the same key overwrite that entry.
        index_to_insert = 0
        overwrite = false
        existing_entry.each do |ae|
          if ae.key == key
            overwrite = true
            break
          end
          index_to_insert += 1
        end
        existing_entry[index_to_insert] = entry
      elsif existing_entry.key == key
        # The existing value is for the identical key. We can safely
        # overwrite
        @btree.insert(hashed_key, entry)
      else
        # There is a single existing entry, but for a different key. Create
        # a new PEROBS::Array and store both entries.
        array_entry = @store.new(Collisions)
        array_entry << existing_entry
        array_entry << entry
        @btree.insert(hashed_key, array_entry)
      end
    else
      # No existing entry. Insert the new entry.
      @btree.insert(hashed_key, entry)
    end
  end
end

#check ⇒ Boolean

Check if the data structure contains any errors.

Returns:

  • (Boolean) —

    true if no erros were found, false otherwise



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# File 'lib/perobs/BigHash.rb', line 226

def check
  @btree.check
end

#delete(key) ⇒ Object

Delete and return the entry for the given key. Return nil if no matching entry exists.

Parameters:

  • key (Integer or String)

Returns:



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# File 'lib/perobs/BigHash.rb', line 170

def delete(key)
  hashed_key = hash_key(key)
  unless (entry = @btree.get(hashed_key))
    return nil
  end

  if entry.is_a?(PEROBS::Array)
    entry.each_with_index do |ae, i|
      return entry.delete_at(i).value if ae.key == key
    end
  elsif entry.key == key
    return entry.value
  end

  nil
end

#each(&block) ⇒ Object

Calls the given block for each key/value pair. @yield(key, value)



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# File 'lib/perobs/BigHash.rb', line 203

def each(&block)
  @btree.each do |_, entry|
    if entry.is_a?(Collisions)
      break if entry.each do |c_entry|
        yield(c_entry.key, c_entry.value)
      end.nil?
    else
      yield(entry.key, entry.value)
    end
  end
end

#empty? ⇒ TrueClass, FalseClass

Return true if hash is empty. False otherweise.

Returns:

  • (TrueClass, FalseClass) 


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# File 'lib/perobs/BigHash.rb', line 197

def empty?
  @btree.entry_counter.zero?
end

#has_key?(key) ⇒ TrueClass or FalseClass Also known as: include?

Check if the is a value stored for the given key.

Parameters:

  • key (Integer or String)

Returns:

  • (TrueClass or FalseClass) 


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# File 'lib/perobs/BigHash.rb', line 147

def has_key?(key)
  hashed_key = hash_key(key)
  unless (entry = @btree.get(hashed_key))
    return false
  end

  if entry.is_a?(PEROBS::Array)
    entry.each do |ae|
      return true if ae.key == key
    end
  elsif entry.key == key
    return true
  end

  false
end

#keys ⇒ Array

This is mostly intended for debugging as the result can be very big. It returns an Array of keys stored in the hash.

Returns:

  • (Array) —

    A list of all keys



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# File 'lib/perobs/BigHash.rb', line 218

def keys
  ks = []
  each { |k, _| ks << k }
  ks
end

#length ⇒ Integer Also known as: size

Return the number of entries stored in the hash.

Returns:

  • (Integer) 


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# File 'lib/perobs/BigHash.rb', line 189

def length
  @btree.entry_counter
end

#restore ⇒ Object 



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# File 'lib/perobs/BigHash.rb', line 77

def restore; end