让数据跳舞(Making Data Dance，Ruby与SQL优化重构) by barrettclark

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让数据跳舞(Making Data Dance，Ruby与SQL优化重构) by barrettclark

发布者 ruby

发布于 1445475435107 浏览 5886 关键词 ruby, PostgreSQL, English

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第1页

Making Data Dance

@barrettclark

第2页

Harness Heretical Antipatterns

For Fun And Proﬁt

第3页

My Resume

第4页

}

My Resume

DATA + +

第5页

ActiveRecord

第6页

Raw SQL

• Complicated joins • Deeper database functionality

第7页

But database portability?!

第8页

https://ﬂic.kr/p/eg4hih

第9页

It just doesn’t work like that.

Database Portability Pipe Dream

第10页

You chose the ___ database for a reason

Use it.

第11页

Caveats

• 500ms • Database connection pool

第12页

Let’s get our hands dirty

第13页

Window Functions

第14页

A window function performs a calculation across a set of table rows that are somehow related to the

current row.

–PostgreSQL 9.4.0 Documentation

第15页

Fold data from other rows into this row.

–Barrett Clark

第16页

Window Function Greatest Hits

•lead() •lag() •first_value() •last_value() •row_number()

第17页

id fruit 1 apple 2 apple 3 apple 4 pear 5 apple 6 pear 7 pear 8 pear 9 pear 10 banana

第18页

SELECT *, LEAD(id) OVER(), LAG(id) OVER() FROM fruits;

id | fruit | lead | lag

----+--------+------+-----

1 | apple | 2 |

2 | apple | 3 | 1

3 | apple | 4 | 2

4 | pear | 5 | 3

5 | apple | 6 | 4

6 | pear | 7 | 5

7 | pear | 8 | 6

8 | pear | 9 | 7

9 | pear | 10 | 8

10 | banana |

|9

(10 rows)

http://sqlﬁddle.com/#!15/230c3b/2

第19页

A window function performs a calculation across a set of table rows that are somehow related to the

current row.

–PostgreSQL 9.4.0 Documentation

第20页

https://ﬂic.kr/p/7KGqEY

第21页

第22页

SELECT *, FIRST_VALUE(id) OVER(PARTITION BY fruit ORDER BY id), ROW_NUMBER() OVER(PARTITION BY fruit ORDER BY id)

FROM fruits;

id | fruit | first_value | row_number

----+--------+-------------+------------

1 | apple |

1| 1

2 | apple |

1| 2

3 | apple |

1| 3

5 | apple |

1| 4

10 | banana |

10 |

4 | pear |

4| 1

6 | pear |

4| 2

7 | pear |

4| 3

8 | pear |

4| 4

9 | pear |

4| 5

(10 rows)

http://sqlﬁddle.com/#!15/230c3b

第23页

Practical Example

Chat App

第24页

SELECT id, message, room_id, user_id FROM messages ORDER BY id;

id |

message

| room_id | user_id

----+-----------------------------+---------+---------

1 | Leaving for the airport now |

1 | 1337

2 | Flight just landed!

| 1 | 1337

3 | waiting on an uber

| 2 | 1337

4 | omw y'all!

| 1 | 1337

9 | hello, world

| 1 | 27

(5 rows)

第25页

Look ahead

SELECT id, message, room_id, user_id, LEAD(user_id) OVER(PARTITION BY room_id ORDER BY room_id, id) AS next_user_id

FROM messages ORDER BY 3, 1;

Deﬁnes the groups of rows to evaluate against the current row

第26页

SELECT id, message, room_id, user_id, LEAD(user_id) OVER(PARTITION BY room_id ORDER BY room_id, id) AS next_user_id

FROM messages ORDER BY 3, 1;

id |

message

| room_id | user_id | next_user_id

----+-----------------------------+---------+---------+--------------

1 | Leaving for the airport now |

1 | 1337 |

2 | Flight just landed!

| 1 | 1337 |

4 | omw y'all!

| 1 | 1337 |

9 | hello, world

| 1 | 27 |

3 | waiting on an uber

| 2 | 1337 |

(5 rows)

第27页

12 3 4 5

SELECT id, message, room_id, user_id, LEAD(user_id) OVER(PARTITION BY room_id ORDER BY room_id, id) AS next_user_id

FROM messages ORDER BY 3, 1;

ProTip™

第28页

class Message < ActiveRecord::Base def self.window_example sql = <<-SQL SELECT id, message, room_id, user_id, LEAD(user_id) OVER(PARTITION BY room_id ORDER BY id) AS next_user_id FROM messages ORDER BY 3, 1; SQL connection.execute(sql) end

end

Returns array of Message objects with additional calculated ﬁelds

第29页

Too anti pattern for you?

第30页

module PGConnection

def conn

config = YAML.load_file(File.open('config/database.yml'))['development']

@conn ||= PG.connect(

:dbname => config['database'],

:user

=> config['username'],

:password => config['password'],

:host

=> config['host'] || 'localhost'

)

end

end

class Antipattern extend PGConnection

def self.window_example

sql = <<-SQL

SELECT id, message, room_id, user_id,

LEAD(user_id) OVER(PARTITION BY room_id ORDER BY id) AS next_user_id

FROM messages

ORDER BY 3, 1;

SQL

conn.exec(sql).values

end end

Returns array of arrays of values

第31页

Models do not have to be backed by ActiveRecord.

Or even persisted in the database.

第32页

Questions We Can Now Answer

• When did something change? • When did someone leave a place?

• How long did each thing last? • How long did people stay in which places?

• Enter / Exit events

第33页

Subqueries

第34页

Subquery

• Subquery to ﬁlter and group • Subquery for a ﬁeld value • Subquery in a join

第35页

Base Query

第36页

SELECT id, phone, major, minor, reading_timestamp, LEAD(minor) OVER ( PARTITION BY phone ORDER BY phone, reading_timestamp ) AS next_minor

FROM beacon_readings ORDER BY 2, 5;

“For a given phone, pull in the next minor ﬁeld”

第37页

When did something change?

第38页

SELECT major, minor, next_minor, COUNT(*) FROM (

SELECT id, phone, major, minor, reading_timestamp, LEAD(minor) OVER ( PARTITION BY phone ORDER BY phone, reading_timestamp) AS next_minor

FROM beacon_readings ORDER BY 2, 5 ) AS beacon_readings_lead WHERE major = 1 AND minor != next_minor GROUP BY major, minor, next_minor ORDER BY major, minor, next_minor;

第39页

Yo dawg, I heard you like queries

第40页

第41页

major | minor | next_minor | count

-------+-------+------------+-------

1| 0|

1 | 18

1| 0|

2| 3

1| 0|

3 | 23

1| 0|

4| 7

1| 1|

0 | 19

1| 1|

2 | 59

1| 1|

3 | 158

1| 1|

4 | 44

1| 2|

0| 5

1| 2|

1 | 59

1| 2|

3 | 85

1| 2|

4 | 40

1| 3|

0 | 21

1| 3|

1 | 154

1| 3|

2 | 85

1| 3|

4 | 52

1| 4|

0| 6

1| 4|

1 | 49

1| 4|

2 | 42

1| 4|

3 | 45

(20 rows)

第43页

Refactor

第44页

https://ﬂic.kr/p/9tT9Yh

第45页

CTE

Common Table Expression

第46页

第47页

WITH beacon_readings_lead_lag AS ( SELECT id, phone, major, minor, reading_timestamp, LEAD(minor) OVER ( PARTITION BY phone ORDER BY phone, reading_timestamp ) AS next_minor FROM beacon_readings ORDER BY 2, 5

) SELECT major, minor, next_minor, COUNT(*) FROM beacon_readings_lead_lag WHERE major = 1

AND minor != next_minor GROUP BY major, minor, next_minor ORDER BY major, minor, next_minor;

第48页

WITH interval_query AS ( SELECT (ts ||' hour')::INTERVAL AS hour_interval FROM generate_series(0,23) AS ts

), time_series AS ( SELECT DATE_TRUNC('hour', NOW()) + INTERVAL '60 min' * ROUND(DATE_PART('minute', NOW()) / 60.0) interval_query.hour_interval AS start_time FROM interval_query

), time_intervals AS ( SELECT start_time, start_time + '1 hour'::INTERVAL AS end_time FROM time_series ORDER BY start_time

), reading_counts AS ( SELECT f.start_time, f.end_time, br.minor, COUNT(DISTINCT br.phone) readings FROM beacon_readings br RIGHT JOIN time_intervals f ON br.reading_timestamp >= f.start_time AND br.reading_timestamp < f.end_time AND br.major = 1 GROUP BY f.start_time, f.end_time, br.minor ORDER BY f.start_time, br.minor

) SELECT * FROM reading_counts;

第50页

Repetition Repetition RepetitionRepetition

Repetition Repetition Repetition Repetition Repetition Repetition Repetition Repetition Repetition Repetition Repetition Repetition Repetition Repetition Repetition

Repetition Repetition Repetition Repetition Repetition Repetition Repetition Repetition Repetition Repetition Repetition

第51页

View

Stored Query

第52页

CREATE OR REPLACE VIEW beacon_readings_lead_view AS

SELECT id, phone, major, minor, reading_timestamp, LEAD(minor) OVER ( PARTITION BY phone ORDER BY phone, reading_timestamp ) AS next_minor

FROM beacon_readings ORDER BY 2, 5 ;

第53页

class CreateLeadView < ActiveRecord::Migration def up execute <<-SQL.strip_heredoc CREATE OR REPLACE VIEW beacon_readings_lead_view AS SELECT ID, phone, major, minor, reading_timestamp, LEAD(minor) OVER ( PARTITION BY phone ORDER BY phone, reading_timestamp ) AS next_minor FROM beacon_readings ORDER BY phone, reading_timestamp; SQL

end

def down sql = "DROP VIEW IF EXISTS beacon_readings_lead_view;" execute(sql)

end end

第54页

SELECT major, minor, next_minor, COUNT(*) FROM beacon_readings_lead_view WHERE major = 1

AND minor != next_minor GROUP BY major, minor, next_minor ORDER BY major, minor, next_minor;

第55页

Business Logic

In The Database?!?

😱😱😱

第56页

YOU

Get to decide where your code runs

第57页

https://ﬂic.kr/p/2MW7SY

第58页

My query is too slow 😢

第59页

Do the heavy lifting in a separate process

第60页

Materialized View

Stored Query And Data

第61页

CREATE MATERIALIZED VIEW beacon_readings_lead_lag_mv AS SELECT * FROM beacon_readings_lead_lag_view WHERE reading_timestamp >= NOW() - '1 day'::INTERVAL;

CREATE INDEX index_beacon_readings_mv_on_major ON beacon_readings_lead_lag_mv USING btree(major ASC NULLS LAST);

CREATE INDEX index_beacon_readings_mv_on_phone ON beacon_readings_lead_lag_mv USING btree(phone COLLATE "default" ASC NULLS LAST);

CREATE INDEX index_beacon_readings_mv_on_reading_timestamp ON beacon_readings_lead_lag_mv USING btree(reading_timestamp ASC NULLS LAST);

第62页

DATA

https://ﬂic.kr/p/khS6jn

第63页

REFRESH MATERIALIZED VIEW CONCURRENTLY beacon_readings_lead_lag_mv;

New in 9.4!

第64页

namespace :db do namespace :heroku do # https://devcenter.heroku.com/articles/scheduler desc 'Update the materialized view(s)' task :update_materialized_view => :environment do sql = 'REFRESH MATERIALIZED VIEW beacon_readings_lead_lag_mv;' ActiveRecord::Base.connection.execute(sql) end end

end

第65页

namespace :db do namespace :heroku do desc "Load the PROD database from Heroku to the local dev database" task :load => :environment do if Rails.env == 'development' Bundler.with_clean_env do config = Rails.configuration.database_configuration[Rails.env] system <<-CMD heroku pgbackups:capture --expire curl -o latest.dump `heroku pgbackups:url` pg_restore --verbose --clean --no-acl --no-owner -h localhost \ -U #{config["username"]} -d #{config["database"]} latest.dump rm -rf latest.dump CMD end end end end

end

https://gist.github.com/barrettclark/c94467e3872d16b3f8b0

第66页

https://ﬂic.kr/p/bVUL7

第67页

Subquery For A Field Value

第68页

SELECT

id,

phone,

( SELECT MIN(id)

FROM beacon_readings_lead_lag_mv

WHERE

major

= br1.major

AND minor = 0

AND phone = br1.phone

AND id >= br1.id

) AS session_close_id,

minor,

next_beacon_minor,

reading_timestamp

FROM beacon_readings_lead_lag_mv br1

WHERE major = 2

AND minor != next_beacon_minor

ORDER BY phone, reading_timestamp;

第69页

第71页

Other Useful Things

第72页

Datatypes

• Array • DateRange and TSRange • JSON • JSONB (9.4) • UUID

http://edgeguides.rubyonrails.org/active_record_postgresql.html

第73页

Future You Will Thank You

第74页

Postgres

• Heroku’s Postgres.app (ships with PostGIS baked in) • Current Version = 9.4

• Database Tools • pgAdmin3 (free) • Navicat (several offerings, free trials)

• Visual Queryplan: http://explain.depesz.com/

第76页

Recap

第77页

It’s OK to write SQL

第78页

Refactor

• Common Table Expression (CTE) • View • Materialized View

第79页

Not saying do everything in the database

第80页

PostgreSQL is awesome

第81页

Thank You.

第82页

Barrett Clark

@barrettclark