Hi all,

I am asking in this list because, at the end of the day, this is a
performance question.

I am looking at writing a search engine of sorts for my database. I
have only ever written very simple search engines before which amounted
to not much more that the query string being used with ILIKE on a pile
of columns. This was pretty rudimentary and didn't offer anything like
relevance sorting and such (I'd sort by result name, age or whatnot).

So I am hoping some of you guys and gals might be able to point me
towards some resources or offer some tips or gotcha's before I get
started on this. I'd really like to come up with a more intelligent
search engine that doesn't take two minutes to return results. I
know, in the end good indexes and underlying hardware will be important,
but a sane as possible query structure helps to start with.

Thanks all!!

Madison

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Madison Kelly wrote:
> Hi all,
>
> I am asking in this list because, at the end of the day, this is a
> performance question.
>
> I am looking at writing a search engine of sorts for my database. I
> have only ever written very simple search engines before which amounted
> to not much more that the query string being used with ILIKE on a pile
> of columns. This was pretty rudimentary and didn't offer anything like
> relevance sorting and such (I'd sort by result name, age or whatnot).
>
> So I am hoping some of you guys and gals might be able to point me
> towards some resources or offer some tips or gotcha's before I get
> started on this. I'd really like to come up with a more intelligent
> search engine that doesn't take two minutes to return results. I
> know, in the end good indexes and underlying hardware will be important,
> but a sane as possible query structure helps to start with.

See search.postgresql.org, you can download all source from
gborg.postgresql.org.

Joshua D. Drake


>
> Thanks all!!
>
> Madison
>
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>
> http://archives.postgresql.org
>


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Joshua D. Drake wrote:
> Madison Kelly wrote:
>> Hi all,
>>
>> I am asking in this list because, at the end of the day, this is a
>> performance question.
>>
>> I am looking at writing a search engine of sorts for my database. I
>> have only ever written very simple search engines before which amounted
>> to not much more that the query string being used with ILIKE on a pile
>> of columns. This was pretty rudimentary and didn't offer anything like
>> relevance sorting and such (I'd sort by result name, age or whatnot).
>>
>> So I am hoping some of you guys and gals might be able to point me
>> towards some resources or offer some tips or gotcha's before I get
>> started on this. I'd really like to come up with a more intelligent
>> search engine that doesn't take two minutes to return results. I
>> know, in the end good indexes and underlying hardware will be important,
>> but a sane as possible query structure helps to start with.
>
> See search.postgresql.org, you can download all source from
> gborg.postgresql.org.

Joshua,

What's the name of the project referred to? There's nothing named
"search" hosted on Gborg according to this project list:

http://gborg.postgresql.org/project/projdisplaylist.php

Madison,

For small data sets and simpler searches, the approach you have been
using can be appropriate. You may just want to use a small tool in a
regular programming language to help build the query. I wrote such a
tool for Perl:

http://search.cpan.org/~markstos/SQL...ywordSearch.pm

For large or complex searches, a more specialized search system may be
appropriate. I suspect that's kind of tool that Joshua is referencing.

Mark

>>> So I am hoping some of you guys and gals might be able to point me
>>> towards some resources or offer some tips or gotcha's before I get
>>> started on this. I'd really like to come up with a more intelligent
>>> search engine that doesn't take two minutes to return results. I
>>> know, in the end good indexes and underlying hardware will be important,
>>> but a sane as possible query structure helps to start with.
>> See search.postgresql.org, you can download all source from
>> gborg.postgresql.org.
>
> Joshua,
>
> What's the name of the project referred to? There's nothing named
> "search" hosted on Gborg according to this project list:
>
> http://gborg.postgresql.org/project/projdisplaylist.php

http://gborg.postgresql.org/project/...rojdisplay.php


--

=== The PostgreSQL Company: Command Prompt, Inc. ===
Sales/Support: +1.503.667.4564 || 24x7/Emergency: +1.800.492.2240
Providing the most comprehensive PostgreSQL solutions since 1997
http://www.commandprompt.com/

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Mark Stosberg wrote:
> Joshua D. Drake wrote:
>> Madison Kelly wrote:
>>> Hi all,
>>>
>>> I am asking in this list because, at the end of the day, this is a
>>> performance question.
>>>
>>> I am looking at writing a search engine of sorts for my database. I
>>> have only ever written very simple search engines before which amounted
>>> to not much more that the query string being used with ILIKE on a pile
>>> of columns. This was pretty rudimentary and didn't offer anything like
>>> relevance sorting and such (I'd sort by result name, age or whatnot).
>>>
>>> So I am hoping some of you guys and gals might be able to point me
>>> towards some resources or offer some tips or gotcha's before I get
>>> started on this. I'd really like to come up with a more intelligent
>>> search engine that doesn't take two minutes to return results. I
>>> know, in the end good indexes and underlying hardware will be important,
>>> but a sane as possible query structure helps to start with.
>> See search.postgresql.org, you can download all source from
>> gborg.postgresql.org.
>
> Joshua,
>
> What's the name of the project referred to? There's nothing named
> "search" hosted on Gborg according to this project list:
>
> http://gborg.postgresql.org/project/projdisplaylist.php
>
> Madison,
>
> For small data sets and simpler searches, the approach you have been
> using can be appropriate. You may just want to use a small tool in a
> regular programming language to help build the query. I wrote such a
> tool for Perl:
>
> http://search.cpan.org/~markstos/SQL...ywordSearch.pm
>
> For large or complex searches, a more specialized search system may be
> appropriate. I suspect that's kind of tool that Joshua is referencing.
>
> Mark
>
> ---------------------------(end of broadcast)---------------------------
> TIP 6: explain analyze is your friend
>

Thanks Joshua and Mark!

Joshua, I've been digging around the CVS (web) looking for the search
engine code but so far have only found the reference (www.search) in
'general.php' but can't locate the file. You wouldn't happen to have a
direct link would you?

Mark, Thanks for a link to your module. I'll take a look at it's
source and see how you work your magic.

I think the more direct question I was trying to get at is "How do
you build a 'relavence' search engine? One where results are
returned/sorted by relevance of some sort?". At this point, the best I
can think of, would be to perform multiple queries; first matching the
whole search term, then the search term starting a row, then ending a
row, then anywhere in a row and "scoring" the results based on which
query they came out on. This seems terribly cumbersome (and probably
slow, indexes be damned) though. I'm hoping there is a better way!

Madi

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> Joshua, I've been digging around the CVS (web) looking for the search
> engine code but so far have only found the reference (www.search) in
> 'general.php' but can't locate the file. You wouldn't happen to have a
> direct link would you?

It's all in module "portal". You will find the indexing stuff in
tools/search, and the search interface in system/page/search.php.

> I think the more direct question I was trying to get at is "How do you
> build a 'relavence' search engine? One where results are returned/sorted
> by relevance of some sort?". At this point, the best I can think of,
> would be to perform multiple queries; first matching the whole search
> term, then the search term starting a row, then ending a row, then
> anywhere in a row and "scoring" the results based on which query they
> came out on. This seems terribly cumbersome (and probably slow, indexes
> be damned) though. I'm hoping there is a better way!

The tsearch2 ranking features are pretty good.

//Magnus


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Madison Kelly wrote:
>
> I think the more direct question I was trying to get at is "How do you
> build a 'relavence' search engine? One where results are returned/sorted
> by relevance of some sort?". At this point, the best I can think of,
> would be to perform multiple queries; first matching the whole search
> term, then the search term starting a row, then ending a row, then
> anywhere in a row and "scoring" the results based on which query they
> came out on. This seems terribly cumbersome (and probably slow, indexes
> be damned) though. I'm hoping there is a better way!

Madison,

I think your basic thinking is correct. However, the first "select" can
done "offline" -- sometime beforehand.

For example, you might create a table called "keywords" that includes
the list of words mined in the other tables, along with references to
where the words are found, and how many times they are mentioned.

Then, when someone actually searches, the search is primarily on the
"keywords" table, which is now way to sort by "rank", since the table
contains how many times each keyword matches. The final result can be
constructed by using the details in the keywords table to pull up the
actual records needed.

My expectation however is that there are enough details in the system,
that I would first look at trying a package like tsearch2 to help solve
the problem, before trying to write another system like this from scratch.

Mark


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Mark Stosberg wrote:
> Madison Kelly wrote:
>> I think the more direct question I was trying to get at is "How do you
>> build a 'relavence' search engine? One where results are returned/sorted
>> by relevance of some sort?". At this point, the best I can think of,
>> would be to perform multiple queries; first matching the whole search
>> term, then the search term starting a row, then ending a row, then
>> anywhere in a row and "scoring" the results based on which query they
>> came out on. This seems terribly cumbersome (and probably slow, indexes
>> be damned) though. I'm hoping there is a better way!
>
> Madison,
>
> I think your basic thinking is correct. However, the first "select" can
> done "offline" -- sometime beforehand.
>
> For example, you might create a table called "keywords" that includes
> the list of words mined in the other tables, along with references to
> where the words are found, and how many times they are mentioned.
>
> Then, when someone actually searches, the search is primarily on the
> "keywords" table, which is now way to sort by "rank", since the table
> contains how many times each keyword matches. The final result can be
> constructed by using the details in the keywords table to pull up the
> actual records needed.
>
> My expectation however is that there are enough details in the system,
> that I would first look at trying a package like tsearch2 to help solve
> the problem, before trying to write another system like this from scratch.
>
> Mark

Now see, this is exactly the kind of sagely advice I was hoping for!

I'll look into tsearch2, and failing that for some reason, I love the
keyword table idea.

Thanks kindly!!

Madi

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>
> Now see, this is exactly the kind of sagely advice I was hoping for!
>
> I'll look into tsearch2, and failing that for some reason, I love the
> keyword table idea.

For example keyword search code, you can try this package:

http://downloads.sourceforge.net/cas...7&big_mirror=0

There is a "keywords" subdirectory with the Perl and SQL. I'm sure this
code is not ideal in a number of ways:

1. It's from 2001.
2. It doesn't actually function on it's own anymore. However, you can
read the code and get ideas.
3. I'm sure someone has a better looking/functioning example!

Anyway, it's there if you want to take a look.

Mark

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On Mon, 2007-02-26 at 11:29 -0500, Madison Kelly wrote:
> I am looking at writing a search engine of sorts for my database. I
> have only ever written very simple search engines before which amounted
> to not much more that the query string being used with ILIKE on a pile
> of columns. This was pretty rudimentary and didn't offer anything like
> relevance sorting and such (I'd sort by result name, age or whatnot).

Look at Tsearch2:

http://www.sai.msu.su/~megera/postgres/gist/tsearch/V2/

It has a lot of features for searching, and can make use of powerful
indexes to return search results very quickly. As someone already
mentioned, it also has ranking features.

Regards,
Jeff Davis


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