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Re: tsvector pg_stats seems quite a bit off.

From: Jan Urbański <wulczer(at)wulczer(dot)org>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Jesper Krogh <jesper(at)krogh(dot)cc>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: tsvector pg_stats seems quite a bit off.
Date: 2010-05-30 14:41:40
Message-ID: 1275230500.1541.4.camel@Nokia-N900-42-11 (view raw or flat)
Thread:
Lists: pgsql-hackers
> Jesper Krogh <jesper(at)krogh(dot)cc> writes:
> > On 2010-05-29 15:56, Jan Urbański wrote:
> > > AFAIK statistics for everything other than tsvectors are built based
> > > on the values of whole rows.
> 
> > Wouldn't it make sense to treat array types like the tsvectors?
> 
> Yeah, I have a personal TODO item to look into that in the future.

There were plans to generalise the functions in ts_typanalyze and use LC for array types as well. If one day I'd find myself with a lot of free time I'd take a stab at that.

> > > The results are attached in a text (CSV) file, to preserve
> > > formatting. Based on them I'd like to propose top_stopwords and
> > > error_factor to be 100.
> 
> > I know it is not percieved the correct way to do things, but I would
> > really like to keep the "stop words" in the dataset and have
> > something that is robust to that.
> 
> Any stop words would already have been eliminated in the transformation
> to tsvector (or not, if none were configured in the dictionary setup).
> We should not assume that there are any in what ts_typanalyze is seeing.

Yes, and as a side note, if you want to be indexing stopwords, just don't pass a stopword file when creating the text search dictionary (or pass a custom one).

> 
> I think the only relevance of stopwords to the current problem is that
> *if* stopwords have been removed, we would see a Zipfian distribution
> with the first few entries removed, and I'm not sure if it's still
> really Zipfian afterwards.    However, we only need the assumption of
> Zipfianness to compute a target frequency cutoff, so it's not like
> things will be completely broken if the distribution isn't quite
> Zipfian.

That's why I was proposing to take s = 0.07 / (MCE-count + 10). But that probably doesn't matter much.

Jan

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