Re: Understanding "seq scans"

Merlin Moncure <mmoncure(at)gmail(dot)com> writes:

> On Tue, Oct 13, 2015 at 11:54 AM, Alvaro Herrera
> <alvherre(at)2ndquadrant(dot)com> wrote:

>> 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.
>
> Note, you can optimize LIKE '%foo%' with pg_trgm/gin indexing.
> Trigram based indexing is kind of a mixed bag but is about to get a
> lot faster with recent enhancements so that it should mostly match or
> beat the brute force search.

Right, it is indeed very efficient, in particular when trying it on PG
9.5b1! Thank you. As a bonus, it is case insensitive, so even ILIKE can take
advantage of it.

> This is the preferred solution if you need to do partial string matching --
> for most other cases of attribute searching I'd be looking at jsonb.

Speaking of which, as this is exactly the goal of my experiments, I have now
added one trigram index for each "key" of an hstore field, where the "key" is
the user language and the value is a text in that language:

CREATE INDEX "text_it_idx" ON test_hstore USING gin ((text->'it') gin_trgm_ops)
CREATE INDEX "text_en_idx" ON test_hstore USING gin ((text->'en') gin_trgm_ops)

Is this the right approach, or am I missing something clever that would allow
me to have a single index?

> Welcome to postgres OP!

Thank you.

Even if I'm not exactly new to PG, I'm very glad to have at least a little
opportunity to convince my coworkers to replace an awful MySQL subsystem with
a shiny new implementation based on PostgreSQL!

bye, lele.
--
nickname: Lele Gaifax | Quando vivrò di quello che ho pensato ieri
real: Emanuele Gaifas | comincerò ad aver paura di chi mi copia.
lele(at)metapensiero(dot)it | -- Fortunato Depero, 1929.