Talk:Extendible hashing

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Implementations

I just found that gdbm implements this algorithm. Might be of interest for students. --phil (talk) 20:51, 26 June 2009 (UTC)[reply]

Ronald Fagin has his own page here on Wikipedia, how to link it? I ? Unicode (talk) 12:40, 10 September 2009 (UTC)[reply]

Sample Code

I think i found a bug in the implementation: What happens if during a split the items of the bucket can't be redistributed (i.e. all items stay in one bucket) because one additional bit is not enough to distinguish between the hashvalues of the key.

Example

I try to add subsequently keys whose hashvalues are (I use the most significant bits). The capacity of my buckets are 1.

100
110

in the beginning everything is empty

gd=0        
[---] ---> [---] d=0

Adding 001

gd=0       
[---] ---> [100]        d=0

Adding 011

[---] ---> [100] + 110  d=0  bucket is full => initiate split
                                               result of split: [100] d=1 [---] d=1

split according to most significant bit => *boom* all key-values stay in one bucket

the right thing to do would be doubling the directory more than once

or more algorithmically speaking: double size of directory until at least one value of the bucket to split is moved into the new bucket

situation after *one* split and *one* doubling of directory

gd=1
[0--] --- > [100] + 110 d=1 
[1--] --- > [---]       d=1

=> double directory and split *again*   result of split [100] d=2 [110] d=2

gd=2
[00-] ---> [---]
[01-] -------^
[10-] ---> [100]
[11-] ---> [110]

212.5.16.228 (talk) 16:38, 1 July 2010 (UTC)[reply]