This document discusses PostgreSQL indexes for web developers using Rails. It covers what indexes are, how to create multiple indexes, GIN and GiST indexes, n-gram indexes, full-text search, and provides some tips. The document includes an agenda, explanations of indexes like B-Trees and how indexes are stored physically, examples of using n-gram and full-text search indexes, and references for further reading.

1. PRACTICAL POSGRESQL INDEXES FOR WEB
DEVELOPER (RAILS)
Long Nguyen
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2. AGENDA
> What is index
> Multiple indexes
> Gin and Gist
> N-gram indexes
> Full-text search
> Couple of tips
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3. WHAT IS INDEX ?
> Default will be BTree. They are
balanced: B-Trees evenly distribute
the keys among the nodes, minimizing
the number of times we have to follow
a pointer from one node to another.
Each pointer leads to a child node that
contains more or less the same number
of keys each other child node does.
> What happen when we create a new
index is that. PG will create actual
physical file in the system to keep
track of those indexes.
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4. MULTIPLE INDEXES
> https://wiki.postgresql.org/images/0/0b/
PGforSmarties.pdf
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5. N-GRAM
create extension pg_trgm;
select show_trgm('alice');
select * from members where first_name like '%Alice%';
CREATE INDEX CONCURRENTLY index_members_on_firstname_trigram
ON members
USING gin (first_name gin_trgm_ops);
drop index index_members_on_firstname_trigram;
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6. FULL-TEXT SEARCH
> https://kvyengineering.com/2016/03/30/understand-
more-about-full-text-search-for-rails-developer/
> From ... like '%name%' ... to full-text search
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7. GIN & GIST
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8. DO YOU SQL CAN DO THIS ? !
WITH RECURSIVE
x(i) AS ( VALUES(0) UNION ALL SELECT i + 1 FROM x WHERE i < 101),
Z(Ix, Iy, Cx, Cy, X, Y, I) AS (
SELECT Ix, Iy, X::float, Y::float, X::float, Y::float, 0
FROM
(SELECT -2.2 + 0.031 * i, i FROM x) AS xgen(x,ix)
CROSS JOIN
(SELECT -1.5 + 0.031 * i, i FROM x) AS ygen(y,iy)
UNION ALL
SELECT Ix, Iy, Cx, Cy, X * X - Y * Y + Cx AS X, Y * X * 2 + Cy, I + 1
FROM Z
WHERE X * X + Y * Y < 16.0
AND I < 27
),
Zt (Ix, Iy, I) AS (
SELECT Ix, Iy, MAX(I) AS I
FROM Z
GROUP BY Iy, Ix
ORDER BY Iy, Ix
)
SELECT array_to_string(
array_agg(
SUBSTRING(
' .,,,-----++++%%%%@@@@#### ',
GREATEST(I,1),
1
)
),''
)
FROM Zt
GROUP BY Iy
ORDER BY Iy;
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9. REFERENCES
> http://blog.codeship.com/discovering-computer-
science-behind-postgres-indexes/
> https://wiki.postgresql.org/images/0/0b/
PGforSmarties.pdf
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