Linked List versus Hashed Linked iIst

[Ashok Babu]

Nick,

The mailing list is not answered by ATM or Google search engine, where you
can play around with any questions you like.
It takes so much efforts for a person to understand the questions, and
reply to that. You need to respect the value of a reply and the value of
time spent by REAL people.

Look at your first question, and after a long reply from GREG, you are
asking a totally different question.


Thanks
Ashok


On Tue, Aug 19, 2014 at 10:53 AM, Nick Krause <xerofoify at gmail.com> wrote:

> On Mon, Aug 18, 2014 at 7:01 PM, Greg Freemyer <greg.freemyer at gmail.com>
> wrote:
> > On Mon, Aug 18, 2014 at 4:20 PM, Nick Krause <xerofoify at gmail.com>
> wrote:
> >> What are the advantages of the hashed linked list version over the
> >> standard one and does it
> >> increase the memory usage and overhead of the linked list more if I
> >> use a hashed version?
> >
> > Seriously?  Do you know what a hash is?
> >
> > A hash is a well-defined many to one algorithm.
> >
> > If I have a universe of a million items that hash down to 100 unique
> > hashes, then I can group those million items by hash and have 100
> > groups of roughly 10,000 items each.
> >
> > The better the hashing algorithm versus my original universe of 1
> > million items, the more even the distribution.
> >
> > Now that I have 100 segregated groups I can build an array of 100
> > linked lists all maintained separately.
> >
> > Thus:
> >
> > hash_index = my_hash(item)
> >
> > add_item(linked_list[hash_item], item) is how I add my item to the
> > hashed linked list.
> >
> > is_in_list(linked_list[hash_item], item) is how I check to see if my
> > item is already in the list.
> >
> > So in my example I have to have 100 linked lists, but each list is on
> > average 100x smaller than a simple linked list would be.
> >
> > Is adding an item to the hashed linked list faster?
> >
> > Absolutely not, I have to hash the item first then do a normal linked
> > list insertion.  That will always be slower.
> >
> > Is finding the item faster?
> >
> > That is the whole point of the exercise.  The theory is you ONLY use a
> > hashed linked list if the overhead of hashing the item is less than
> > the amount of time saved by traversing shorter lists when you search.
> >
> > It is the job of the programmer to make the determination if a hashed
> > list is a better choice or not on a case by case basis.  It depends on
> > the length of the list without breaking it into pieces and how well
> > the hash algorithm can do at generating roughly similar segregated
> > groups.
> >
> > For the size question, write yourself a userspace app and test it.
> > Obviously that is more work than asking here, but it is ASSUMED you
> > are doing research on your OWN before you post questions here.
> >
> > fyi: this question has little to do with the linux kernel.  It is part
> > of what people mean when they say you need to go learn c before you
> > start on the kernel.  Using linked lists and hashed linked lists is
> > stuff you can fully explore in userspace.
> >
> > Greg
> No I known what the advantages are for user space was wondering if
> there were any issues that differ in
> kernel space.
> Nick
>
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