From: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
---|---|
To: | Lele Gaifax <lele(at)metapensiero(dot)it> |
Cc: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: Understanding "seq scans" |
Date: | 2015-10-12 22:13:09 |
Message-ID: | 20151012221309.GQ4405@alvherre.pgsql |
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Lists: | pgsql-general |
Lele Gaifax wrote:
> Hi all,
>
> I'm doing some experiments to find the better layout for reimplementing
> an existing db (MySQL cough!) with PostgreSQL 9.4+.
>
> I noticed a strange plan coming out from a simple query joining two tables,
> both containing 10Mrecs (and both ANALYZEd):
> -> Bitmap Index Scan on l10n_text_index (cost=0.00..64549.19 rows=999662 width=0)
> Index Cond: ((lower(text) ~>=~ 'quattro'::text) AND (lower(text) ~<~ 'quattrp'::text))
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?
I wonder if the l10n_text_index index should be on (lang, lower(text)).
How often are you going to look for translated text without specifying a
language?
--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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