Re: Understanding "seq scans"

Lele Gaifax wrote:
> Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> writes:
>
> > So 10% of your rows in the master_l10n table start with "quattro"?
> > That's pretty odd, isn't it? How did you manufacture these data?
>
> Well, not a real scenario for sure, but definitely not odd: I just needed an
> "extremely" big dataset to test out several different strategies, both on
> table layout and indexes. The tables are populated by mechanically translating
> the integer primary key into the corresponding "in words" string (1 -> "one")...

I imagined it would be something like that. It's not the most useful
set of test data, precisely because it doesn't accurately reflect what
you're going to have in practice. I suggest you enter some actual text,
even if it's just text from Don Camillo or whatever.

> > How often are you going to look for translated text without specifying a
> > language?
>
> Never. The most frequently used criteria is «LIKE '%word%'» in the context of
> a user session, and thus with a "preferred language".

Be very careful with a % at the left. The index is not going to work at
all there. It is not the same as looking for stuff without a % at the
left.

--
Álvaro Herrera http://www.2ndQuadrant.com/
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