Search speed eclipsed by retrieval speed

Hi all,

I’ve recently started working with Ferret and I’m getting what seems to
be slow searches. I have about 10000 documents in the index, with
several fields per document, with some fields having an array of several
values that are indexed.

I am using a RAMDirectory to store the index for searching. When doing
testing, I find that searches are reasonable at around .2 to .5 seconds
per search (for simple single word searches). However, when trying to
retrieve the documents from the index, to retrieve the results ends up
taking well over 2 to 3 seconds, totally eclipsing the search time, and
making the whole thing quite slow. Am I missing anything here? Will
reducing the document size greatly affect the retrieval time of the
documents? Any suggestions for general speed improvement? Thanks!

Below, I have detailed te process I am using to create and search the
index, in case that’s useful:

I have created an index that is stored on disk. I’d like to read it back
into memory and use a RAMDirectory to see what speed improvements I can
get by using that.

Here’s what I’m doing to create the index:

ram_dir = Ferret::Store::RAMDirectory.new
in_mem_index = Ferret::Index::IndexWriter.new(ram_dir, :create =>
true)

… add stuff to the index

in_mem_index.optimize
in_mem_index.close

index = Ferret::Index::Index.new(:dir => ram_dir)
index.persist(‘path/to/index’, true)
index.close

I use a RAMDirectory when initially writing to the index because I am
writing a lot to the index and I assume writing directly to a
FSDirectory will be slower.

Later, I am trying to load this index back into memory as a
RAMDirectory. I am not actually sure how to do this, so I am guessing
here:

ram_dir = Ferret::Store::RAMDirectory.new
index = Ferret::Index::Index.new(:dir => ram_dir, :create => true)
index.add_indexes(Ferret::Store::FSDirectory.new(‘path/to/index’))

results = []
num_results = index.search_each(‘search word(s)’, { :first_doc => 0,
:num_docs => 50 }) do | doc, score |
results << index[doc]
end

Any help would be awesome. Thanks!

  • chris

On 7/5/06, Chris [email protected] wrote:

retrieve the documents from the index, to retrieve the results ends up
get by using that.
in_mem_index.close

index = Ferret::Index::Index.new(:dir => ram_dir)
index.persist(‘path/to/index’, true)
index.close

Hi Chris,

This is currently the fastest way to create small indexes. In the next
version of Ferret it won’t make any difference though. Ferret will
automatically try and create as much of the index in Memory as
possible. It’s up to you to set the amount of memory that you want to
use to create the index. But forget about that for now. I’ll try and
answer your question.

I use a RAMDirectory when initially writing to the index because I am
writing a lot to the index and I assume writing directly to a
FSDirectory will be slower.

Yes, but not by a lot.

Later, I am trying to load this index back into memory as a
RAMDirectory. I am not actually sure how to do this, so I am guessing
here:

ram_dir = Ferret::Store::RAMDirectory.new
index = Ferret::Index::Index.new(:dir => ram_dir, :create => true)
index.add_indexes(Ferret::Store::FSDirectory.new(‘path/to/index’))

Better to do it like this;

ram_dir = 

Ferret::Store::RAMDirectory.new(FSDirectory.new(“path/to/index”),
true)

That reads and FSDirectory directly into a RAMDirectory.

results = []
num_results = index.search_each(‘search word(s)’, { :first_doc => 0,
:num_docs => 50 }) do | doc, score |
results << index[doc]
end

Any help would be awesome. Thanks!

This all looks fine. It depends on your exact situation but if you are
indexing data from a database it is usually a better idea to only
store the id in the index. That way, when you load the document from
the index, you are only loading one short string. You can then get any
other data you need from the database. If your documents are large,
Ferret needs to read the whole document into memory. I’ve added a lazy
loading document to Ferret which will speed things up a lot in the
next version. It still seems very surprising to me that your queries
are taking so long. Are you working on Windows? That would explain
things a little.

Cheers,
Dave

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