Why is only the suffix of work_index hashed?
- by Jaroslav Záruba
I'm reading through the PDF that Brett Slatkin has published for Google I/O 2010:
"Data pipelines with Google App Engine": http://tinyurl.com/3523mej
In the video (the Fan-in part) Brett says that the work_index has to be a hash, so that 'you distribute the load across the BigTable': http://www.youtube.com/watch?v=zSDC_TU7rtc#t=48m44
...and this is how work_index is created:
work_index = '%s-%d' % (sum_name, knuth_hash(index))
...which I guess creates something like 'mySum-54657651321987'
I do understand the basic idea, but is why only one half of work_index is hashed? Is it important to hash only part of it leaving the suffix out? Would it be wrong to do
md5('%s-%d' % (sum_name, index)) so that the hash would be like '6gw8....hq6'
?
I'm Java guy so I would use md5 to hash, which means I get id like 'mySum' + 32 characters. (Obviously I want my ids/keys to be as short as possible here.) If I could hash the whole string my id would be just 32 chars.
Or would you suggest to use something else to do the hashing with?
