Re: [Boost-users] multi_index_container

Some correction!! in my previous mail. Thank you Mr Lopez,

Slower in which aspect? Insertion, deletion, lookup? I have observed it is slower in insertion. I am roughly creating some 200,000 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 iteration problem in hash -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 i get the last inserted node, how shall i get previously inserted nodes. 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 wrote:

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Hi Aashit,

Aashit Soni ha escrito:

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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?

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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.)

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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_polic...

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.

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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.

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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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