Thread: Data Page

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Has anyone seen a PostgreSQL available approximate string matching
function? I just finished implementing a Wu-Manber k-differences function
for Domino and PL/pgSQL doesn't seem powerful enough to handle the job.

Someone prove me wrong?

Joshua b. Jore
http://www.greentechnologist.org
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Mohammad,

> what is the size of the data page?

PostgreSQL does not use data pages, thanks to TOAST.

> dose the defualt use of postgresql 7.1 use caching?

What do you mean by "caching"?  We use buffers and prepared query
 plans, yes.

-Josh

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Joshua,

> Has anyone seen a PostgreSQL available approximate string matching
> function? I just finished implementing a Wu-Manber k-differences
>  function
> for Domino and PL/pgSQL doesn't seem powerful enough to handle the
>  job.

Err, no offense, but .... English, please?

-Josh

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Ok, the basic question: does anyone have any approximate string matching
algorithms coded such that PostgreSQL can use it effeciently? I would like
to handle inserts/deletes. I already have a perl and LotusScript (that's
for Domino) implementation but I haven't ever been able to get the perl
module to install right with PostgreSQL.

If it comes down to it I may just do the thing as a C function and return
the code to this list. The problem with that is I'm a shaky C programmer
so more experienced folks would need to ensure that I'm not doing
something dodgy. Largely I'm just asking around before I go do it. I
didn't see anything about this on the list achives.

Translations:
Wu-Manber k-differences: it's an algorithm that measures how many edits
are required to turn one string into another. k is the number of edits.
This is also known as the Levenschtein distance. I'm getting this from the
Perl Algorithm book.

Joshua b. Jore
http://www.greentechnologist.org

On Tue, 19 Mar 2002, Josh Berkus wrote:

> Joshua,
>
> > Has anyone seen a PostgreSQL available approximate string matching
> > function? I just finished implementing a Wu-Manber k-differences
> >  function
> > for Domino and PL/pgSQL doesn't seem powerful enough to handle the
> >  job.
>
> Err, no offense, but .... English, please?
>
> -Josh
>
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> TIP 1: subscribe and unsubscribe commands go to majordomo@postgresql.org
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Joshua,

This is *not* a novice question.  I'm not sure where else you'd post it
 though.

> Ok, the basic question: does anyone have any approximate string
>  matching
> algorithms coded such that PostgreSQL can use it effeciently? I would
>  like
> to handle inserts/deletes. I already have a perl and LotusScript
>  (that's
> for Domino) implementation but I haven't ever been able to get the
>  perl
> module to install right with PostgreSQL.

Metaphone, Soundex, and Levenshtein were built for postgresql by Joe
 Conway.   Find them in the /contrib directory.

> Translations:
> Wu-Manber k-differences: it's an algorithm that measures how many
>  edits
> are required to turn one string into another. k is the number of
>  edits.
> This is also known as the Levenschtein distance. I'm getting this
>  from the
> Perl Algorithm book.

Levenschtien is available in /contrib.  It works well for the database
 I use it on; though that only has 7000 records, so you'll have to test
 really large tables.

If you're deduplicating, I wrote a sophisticated name-alike function
 using Levenschtein and Metaphone in PL/pgSQL and posted it to Roberto
 Mello's function library  (accessable from TechDocs).

-Josh Berkus

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So PostgreSQL is supposed to be object-relational. What is that and how
should I design my applications with that in mind? There are plenty of
texts out there on plain'ol RDBMS, I haven't seen anything that takes a
ORDBMS spin on it.

I guess what I'm missing is where or what the objects are. I've already
got overloaded functions and I tried to work with inherited tables (but
they didn't work the way I expected them to). Is that all that ORDBMS is?

About the inherited tables, I had hoped to have a parent with children
where fkey constraints held against the parent and cascaded to the
children (say person id where child tables are different types of people).

Joshua b. Jore
http://www.greentechnologist.org
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Joshua,

> So PostgreSQL is supposed to be object-relational. What is that and
>  how
> should I design my applications with that in mind? There are plenty
>  of
> texts out there on plain'ol RDBMS, I haven't seen anything that takes
>  a
> ORDBMS spin on it.

There's a huge paper on this somewhere in the host of PostgreSQL online
 documentation.  I have a copy as part of the DOSSIER books, but I'm
 not sure where Rich got it.

-Josh Berkus