Re: [Boost-users] multi_index_container

From: Aashit Soni (aks309_at_[hidden])
Date: 2006-02-17 00:56:29

Thank you Mr Lopez,

> Slower in which aspect? Insertion, deletion, lookup?
I have observed it is slower in insertion. I am roughly creation some
2 entries into it. One entry is arround 10 Bytes of information. Each
creation also creates some external objects to that are being cached
in this container.

- I am having some problem in look up also. My hash index is
non_unique. I am not sure how the  collisions are handled? When i call
find and if the collisions are there how shall i iterate so that i get
another element store with in same line.

In some case, i need to reserve  the space for the elements, So when i
create my multi_index container, i want to tell it saying that i need
x amount of space so please do the allocation and keep it ready. Is
such facility available.

I will just incorporate- your sugguesion and check how it is working.

Thank you once again, I really appreciate your time.
regards,
aashit

On 2/16/06, Joaquín Mª López Muñoz <joaquin_at_[hidden]> wrote:
> Hi Aashit,
>
> Aashit Soni ha escrito:
>
> > Hi all,
> >
> > I am using multi_index_container on MSVC6, WinXP. I ported my existing
> > Hash and order list to multi_index_container. which is working quite
> > expected? a pure vanila hash_index with ordered_index
> >
> > I am facing some problem in fine tuning the hash_index which is slower
> > compared to my previous implementation.
>
> Slower in which aspect? Insertion, deletion, lookup?
>
> > I am looking for different
> > ways how can i fine tune the hash_index in multi_index_container?
> >
> > specifically i am yet to discover,
> > How can i set the bucket size for the hash container?
>
> You cannot control bucket size explicitly. Hashed indices occupancy
> level is controlled thru a parameter called load factor (lf) defined as:
>
>  lf=size()/bucket_count()
>
> In general, the lower lf, the faster lookup operations are. You can set
> the maximum value of lf to be allowed with max_load_factor():
>
> float mlf=c.max_load_factor(); // query max lf
> c.max_load_factor(0.8f); // set max lf
>
> When the load factor reaches the specified maximum, the number of
> buckets is automatically increased.
> By default max_load_factor()=1.0. Lower this for faster lookup,
> at the expense of more memory usage (more buckets.)
>
> > How can configure the container for maximum store it can reserve for
> > me in one shot?
>
> Use rehash(), documented at
>
> http://boost.org/libs/multi_index/doc/reference/hash_indices.html#hash_policy
>
> prior to mass insertion of elements. For instance:
>
> // insert 1000000 elements. With lf=1.0, we will need 1000000 buckets
> // so as to be under the specified max load factor
> c.rehash(1000000);
> c.insert(first,last);
>
> Doing a prior rehash is not necessary, but will save you some
> intermediate automatic rehashings, pretty much the same way as
> it happens with std::vector and reserve.
>
> > any other optimization parameter.
> >
>
> Other than this, your best option is to choose a good hashing function.
> The default is expected to work well except for exceptional
> situations. You might want to use the hashing function used in your
> previous Hash container so as to check out whether it does a
> better job than Boost.Hash, although I'd say this is unlikely.
>
> > If any one has some idea. It will be of great help to me.
> >
> > regards,
> > aashit
>
> Hope this helps a little,
>
> Joaquín M López Muñoz
> Telefónica, Investigación y Desarrollo
>
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