Re: Understanding "seq scans" - Mailing list pgsql-general

From Alvaro Herrera
Subject Re: Understanding "seq scans"
Date
Msg-id 20151013165452.GU4405@alvherre.pgsql
Whole thread Raw
In response to Re: Understanding "seq scans"  (Lele Gaifax <lele@metapensiero.it>)
Responses Re: Understanding "seq scans"
List pgsql-general
Lele Gaifax wrote:
> Alvaro Herrera <alvherre@2ndquadrant.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/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


pgsql-general by date:

Previous
From: Mikhail
Date:
Subject: Re[2]: [GENERAL] hanged session on index creation
Next
From: droberts
Date:
Subject: ID column naming convention