CRUD! What to do When Active Record, MySQL, and Your Data Betray You

Slideshow for talk at Mountain West Ruby Conference March 21st, 2014.

Related blog post: http://www.eileencodes.com/posts/crud-what-to-do-when-active-record-mysql-and-your-data-betray-you

The magic of ActiveRecord database interactions is easy to rely on and allows us assume it knows best. Without a solid understanding of how ActiveRecord translates into MySQL, however, significant issues can arise. This is particularly true with large data sets and complex model relationships. My talk explores an example for each CRUD function and shows how these queries can result in MySQL timeouts, memory issues or stack level too deep errors. The examples will examine the consequences of chaining large datasets, uses for Arel, and how to avoid encountering major problems and most importantly, how these queries can be rewritten to run more efficiently.

Transcript

1. CRUD! What to do When
   Active Record,
   MySQL,
   and Your Data
   Betray You
   

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2. eileencodes.com
   @eileencodes
   github.com/eileencodes
   Eileen M. Uchitelle
   

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3. You - Should - Tell
   Uchitelle
   

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4. You - Should - Tell
   Uchitelle
   X
   

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5. Senior Developer at PhishMe
   

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6. * always check where a link
   is going before clicking on it
   

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7. At PhishMe we have A LOT of data
   

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8. Active Record is a magical unicorn
   

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9. When MySQL crashed or my queries were slow
   I felt betrayed by Active Record.
   

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10. But I knew Active Record and I could work it out
    So I began studying my queries more closely...
    

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11. Learn from my mistakes...
    And avoid #firstworldproblems
    

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12. CREATE
    READ
    UPDATE
    DELETE
    

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13. CREATE
    create!, new, INSERT
    

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14. READ
    where, find_each, pluck, SELECT
    

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15. UPDATE
    update_attributes, edit, update_all, UPDATE
    

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16. DELETE
    destroy, delete, destroy_all, delete_all, DELETE
    

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17. Address Book Example ERD
    Users
    first_name string
    last_name string
    email string
    password_digest string
    ...[etc]
    Contacts
    first_name string
    last_name string
    birthday date
    user_id integer
    ...[etc]
    Categories
    name string
    description string
    user_id integer
    Categorizations
    contact_id integer
    category_id integer
    

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18. Address Book Example
    User
    has_many :contacts
    has_many :categories
    Contact
    belongs_to :user
    has_many :categorizations, dependent: :delete_all
    has_many :categories, through: :categorizations
    Category
    belongs_to :user
    has_many :categorizations, dependent: :delete_all
    has_many :contacts, through: :categorizations
    Categorizations
    belongs_to :contact
    belongs_to :category
    

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19. Address Book Example
    User
    has_many :contacts
    has_many :categories
    Contact
    belongs_to :user
    has_many :categorizations, dependent: :delete_all
    has_many :categories, through: :categorizations
    Category
    belongs_to :user
    has_many :categorizations, dependent: :delete_all
    has_many :contacts, through: :categorizations
    Categorizations
    belongs_to :contact
    belongs_to :category
    

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20. Address Book Example
    User
    has_many :contacts
    has_many :categories
    Contact
    belongs_to :user
    has_many :categorizations, dependent: :delete_all
    has_many :categories, through: :categorizations
    Category
    belongs_to :user
    has_many :categorizations, dependent: :delete_all
    has_many :contacts, through: :categorizations
    Categorizations
    belongs_to :contact
    belongs_to :category
    

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21. Address Book Example
    User
    has_many :contacts
    has_many :categories
    Contact
    belongs_to :user
    has_many :categorizations, dependent: :delete_all
    has_many :categories, through: :categorizations
    Category
    belongs_to :user
    has_many :categorizations, dependent: :delete_all
    has_many :contacts, through: :categorizations
    Categorizations
    belongs_to :contact
    belongs_to :category
    

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22. Address Book Example
    User
    has_many :contacts
    has_many :categories
    Contact
    belongs_to :user
    has_many :categorizations, dependent: :delete_all
    has_many :categories, through: :categorizations
    Category
    belongs_to :user
    has_many :categorizations, dependent: :delete_all
    has_many :contacts, through: :categorizations
    Categorizations
    belongs_to :contact
    belongs_to :category
    

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23. CREATE
    

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24. Let’s create 10,000 records the
    Active Record way using a CSV
    CSV.foreach("#{filepath}", headers: true) do |csv|
    Contact.create!({
    first_name: csv[0],
    last_name: csv[1],
    birthday: csv[2],
    ...
    })
    end
    

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25. Let’s create 10,000 records the
    Active Record way using a CSV
    CSV.foreach("#{filepath}", headers: true) do |csv|
    Contact.create!({
    first_name: csv[0],
    last_name: csv[1],
    birthday: csv[2],
    ...
    })
    end
    INSERT INTO `contacts` (`first_name`, `last_name`,
    `birthday`,...) VALUES ('John', 'Smith',
    '1987-02-01',...);
    

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26. MySQL Batch Insert, FTW.
    

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27. Don’t be afraid to write raw SQL
    

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28. Let’s create the same contacts with
    MySQL Batch Insert
    contact_values = []
    CSV.foreach("#{filepath}", headers: true) do |csv|
    contact_values << "('#{csv[0]}','#{csv[1]}','#{csv[2]}'...)"
    end
    batch_size = 2000
    while !contact_values.empty?
    contacts_shifted = contact_values.shift(batch_size)
    contacts_sql = "INSERT INTO contacts(first_name, last_name,
    birthday,...)
    VALUES#{contacts_shifted.join(", ")}"
    ActiveRecord::Base.connection.execute(contacts_sql)
    end
    

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29. Let’s create the same contacts with
    MySQL Batch Insert
    contact_values = []
    CSV.foreach("#{filepath}", headers: true) do |csv|
    contact_values << "('#{csv[0]}','#{csv[1]}','#{csv[2]}'...)"
    end
    batch_size = 2000
    while !contact_values.empty?
    contacts_shifted = contact_values.shift(batch_size)
    contacts_sql = "INSERT INTO contacts(first_name, last_name,
    birthday,...)
    VALUES#{contacts_shifted.join(", ")}"
    ActiveRecord::Base.connection.execute(contacts_sql)
    end
    

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30. Let’s create the same contacts with
    MySQL Batch Insert
    contact_values = []
    CSV.foreach("#{filepath}", headers: true) do |csv|
    contact_values << "('#{csv[0]}','#{csv[1]}','#{csv[2]}'...)"
    end
    batch_size = 2000
    while !contact_values.empty?
    contacts_shifted = contact_values.shift(batch_size)
    contacts_sql = "INSERT INTO contacts(first_name, last_name,
    birthday,...)
    VALUES#{contacts_shifted.join(", ")}"
    ActiveRecord::Base.connection.execute(contacts_sql)
    end
    

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31. Let’s create the same contacts with
    MySQL Batch Insert
    contact_values = []
    CSV.foreach("#{filepath}", headers: true) do |csv|
    contact_values << "('#{csv[0]}','#{csv[1]}','#{csv[2]}'...)"
    end
    batch_size = 2000
    while !contact_values.empty?
    contacts_shifted = contact_values.shift(batch_size)
    contacts_sql = "INSERT INTO contacts(first_name, last_name,
    birthday,...)
    VALUES#{contacts_shifted.join(", ")}"
    ActiveRecord::Base.connection.execute(contacts_sql)
    end
    

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32. Let’s create the same contacts with
    MySQL Batch Insert
    contact_values = []
    CSV.foreach("#{filepath}", headers: true) do |csv|
    contact_values << "('#{csv[0]}','#{csv[1]}','#{csv[2]}'...)"
    end
    batch_size = 2000
    while !contact_values.empty?
    contacts_shifted = contact_values.shift(batch_size)
    contacts_sql = "INSERT INTO contacts(first_name, last_name,
    birthday,...)
    VALUES#{contacts_shifted.join(", ")}"
    ActiveRecord::Base.connection.execute(contacts_sql)
    end
    

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33. Let’s create the same contacts with
    MySQL Batch Insert
    contact_values = []
    CSV.foreach("#{filepath}", headers: true) do |csv|
    contact_values << "('#{csv[0]}','#{csv[1]}','#{csv[2]}'...)"
    end
    batch_size = 2000
    while !contact_values.empty?
    contacts_shifted = contact_values.shift(batch_size)
    contacts_sql = "INSERT INTO contacts(first_name, last_name,
    birthday,...)
    VALUES#{contacts_shifted.join(", ")}"
    ActiveRecord::Base.connection.execute(contacts_sql)
    end
    

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34. Let’s create the same contacts with
    MySQL Batch Insert
    ActiveRecord::Base.connection.execute(contacts_sql)
    INSERT INTO contacts(first_name, last_name,
    birthday,...)
    VALUES('Lauretta','Senger','1987-02-01',...),
    ('Jane','Roob','1987-02-01',...),
    ('Blaze','Lakin','1987-02-01',...),
    ('Elton','Cormier','1987-02-01',...),
    ('John','Kohler','1987-02-01',...),
    ('Clementine','Marvin','1987-02-01',...),
    ('Ova','Aufderhar','1987-02-01',...)
    ...
    

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35. That’s a huge difference
    ActiveRecord Benchmark Data:
    user system total real
    => 44.740000 1.180000 45.920000 ( 51.095556)
    

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36. That’s a huge difference
    ActiveRecord Benchmark Data:
    user system total real
    => 44.740000 1.180000 45.920000 ( 51.095556)
    MySQL Batch Insert Benchmark Data:
    user system total real
    => 2.710000 0.050000 2.760000 ( 3.227031)
    

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37. READ
    

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38. Let’s read some data and output the
    first name of each contact
    Contact.where(user_id: 1, country: “USA”).each do |contact|
    puts contact.first_name
    end
    Contact.where(user_id: 1, country: “USA”).find_each do |contact|
    puts contact.first_name
    end
    Contact.where(user_id: 1, country: “USA”)
    .pluck(:first_name).each do |first_name|
    puts first_name
    end
    

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39. Let’s read some data and output the
    first name of each contact
    Contact.where(user_id: 1, country: “USA”).each do |contact|
    puts contact.first_name
    end
    SELECT `contacts`.* FROM `contacts` WHERE
    `contacts`.`user_id` = 1 AND `contacts`.`country` = 'USA'
    =>
    Lauretta
    Shana
    Jason
    Jermain
    Blaze
    Jessy
    Bradly
    ...
    

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40. Let’s read some data and output the
    first name of each contact
    Contact.where(user_id: 1, country: “USA”).find_each do |contact|
    puts contact.first_name
    end
    SELECT `contacts`.* FROM `contacts` WHERE
    `contacts`.`user_id` = 1 AND `contacts`.`country` = 'USA'
    ORDER BY `contacts`.`id` ASC LIMIT 1000
    =>
    Lauretta
    Shana
    Jason
    ...
    SELECT `contacts`.* FROM `contacts` WHERE `contacts`.`user_id`
    = 1 AND `contacts`.`country` = 'USA' AND (`contacts`.`id` >
    1001) ORDER BY `contacts`.`id` ASC LIMIT 1000
    => ...
    

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41. Let’s read some data and output the
    first name of each contact
    f
    Contact.where(user_id: 1, country: “USA”)
    .pluck(:first_name).each do |first_name|
    puts first_name
    end
    SELECT `contacts`.`first_name` FROM `contacts` WHERE
    `contacts`.`user_id` = 1 AND `contacts`.`country` = 'USA'
    => ["Lauretta", "Shana", "Jason", "Jermain", "Blaze", "Jessy",
    "Bradly", "Emma", "Cruz", "Elton", "Dashawn", "Rosanna", "Ryan",
    "Leonel", "Ashly", "Mittie", "Tobin", "Antonio", "Chad", "Lauryn",
    "Sydnie", "Sebastian", "Johnpaul", "Yasmeen", "Junior", "Monroe",
    "Avery",...]
    

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42. Let’s read some data and output the
    first name of each contact
    Contact.where(user_id: 1, country: “USA”).each do |contact|
    puts contact.first_name
    end
    Contact.where(user_id: 1, country: “USA”).find_each do |contact|
    puts contact.first_name
    end
    Contact.where(user_id: 1, country: “USA”)
    .pluck(:first_name).each do |first_name|
    puts first_name
    end
    

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43. Which one was fastest?
    .each Benchmark Data:
    user system total real
    => 0.950000 0.060000 1.010000 ( 1.050266)
    

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44. Which one was fastest?
    .each Benchmark Data:
    user system total real
    => 0.950000 0.060000 1.010000 ( 1.050266)
    .find_each Benchmark Data:
    user system total real
    => 0.900000 0.040000 0.940000 ( 0.976979)
    

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45. Which one was fastest?
    .each Benchmark Data:
    user system total real
    => 0.950000 0.060000 1.010000 ( 1.050266)
    .find_each Benchmark Data:
    user system total real
    => 0.900000 0.040000 0.940000 ( 0.976979)
    .pluck Benchmark Data:
    user system total real
    => 0.080000 0.020000 0.100000 ( 0.126814)
    

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46. Which one was fastest?
    .each Benchmark Data:
    user system total real
    => 0.950000 0.060000 1.010000 ( 1.050266)
    .find_each Benchmark Data:
    user system total real
    => 0.900000 0.040000 0.940000 ( 0.976979)
    .pluck Benchmark Data:
    user system total real
    => 0.080000 0.020000 0.100000 ( 0.126814)
    

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47. Statistics for Read
    0
    3.8
    7.5
    11.3
    15.0
    0 10 1000 10000 100000
    .each .find_each .pluck
    

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48. Utilizing find_by_sql
    Contact.find_by_sql([
    "SELECT first_name FROM contacts WHERE
    user_id=? AND
    country=? AND birthday > ?",
    1, 'USA','1987-01-01'
    ]).each do |contact|
    puts contact.first_name
    end
    

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49. UPDATE
    

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50. Let’s update the category in
    each categorization
    category = Category.where(name: “Networking”).first
    Categorization.all.each do |categorization|
    categorization.update_attributes(
    category_id: category.id
    )
    end
    

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51. Let’s update the category in
    each categorization
    category = Category.where(name: “Networking”).first
    Categorization.all.each do |categorization|
    categorization.update_attributes(
    category_id: category.id
    )
    end
    UPDATE `categorizations` SET `category_id` = 1 WHERE
    `categorizations`.`id` = 1
    UPDATE `categorizations` SET `category_id` = 1 WHERE
    `categorizations`.`id` = 2
    UPDATE `categorizations` SET `category_id` = 1 WHERE
    `categorizations`.`id` = 3
    

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52. Let’s update the category in
    each categorization
    category = Category.where(name: “Networking”).first
    Categorization.update_all(
    category_id: category.id
    )
    

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53. Let’s update the category in
    each categorization
    category = Category.where(name: “Networking”).first
    Categorization.update_all(
    category_id: category.id
    )
    UPDATE `categorizations` SET
    `categorizations`.`category_id` = 1
    

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54. Check out the difference
    update_attributes Benchmark Data:
    user system total real
    => 12.990000 0.870000 13.860000 ( 17.156265)
    

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55. Check out the difference
    update_attributes Benchmark Data:
    user system total real
    => 12.990000 0.870000 13.860000 ( 17.156265)
    update_all Benchmark Data:
    user system total real
    => 0.000000 0.000000 0.000000 ( 0.042140)
    

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56. DELETE
    

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57. destroy_all vs. delete_all with
    has_many dependencies
    Contact
    has_many :categorizations
    has_many :categories, through: :categorizations
    Category
    has_many :categorizations
    has_many :contacts, through: :categorizations
    Categorizations
    belongs_to :contact
    belongs_to :category
    

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58. f
    f
    destroy_all vs. delete_all with
    has_many dependencies
    Contact
    has_many :categorizations, dependent: :destroy
    has_many :categories, through: :categorizations
    Category
    has_many :categorizations, dependent: :destroy
    has_many :contacts, through: :categorizations
    Contact.destroy_all
    

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59. destroy_all vs. delete_all with
    has_many dependencies
    f
    f
    Contact
    has_many :categorizations, dependent: :destroy
    has_many :categories, through: :categorizations
    Category
    has_many :categorizations, dependent: :destroy
    has_many :contacts, through: :categorizations
    Contact.destroy_all
    SELECT `categorizations`.* FROM `categorizations`
    WHERE `categorizations`.`contact_id` = 1
    DELETE FROM `categorizations` WHERE
    `categorizations`.`id` = 1
    DELETE FROM `contacts` WHERE `contacts`.`id` = 1
    

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60. destroy_all vs. delete_all with
    has_many dependencies
    f
    f
    Contact
    has_many :categorizations, dependent: :delete_all
    has_many :categories, through: :categorizations
    Category
    has_many :categorizations, dependent: :delete_all
    has_many :contacts, through: :categorizations
    Contact.delete_all
    

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61. destroy_all vs. delete_all with
    has_many dependencies
    f
    f
    Contact
    has_many :categorizations, dependent: :delete_all
    has_many :categories, through: :categorizations
    Category
    has_many :categorizations, dependent: :delete_all
    has_many :contacts, through: :categorizations
    Contact.delete_all
    DELETE FROM `contacts`
    

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62. destroy_all vs. delete_all with
    has_many dependencies
    f
    f
    Contact
    has_many :categorizations
    has_many :categories, through: :categorizations
    Category
    has_many :categorizations
    has_many :contacts, through: :categorizations
    Contact.delete_all
    Contact.destroy_all
    

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63. destroy_all vs. delete_all with
    has_many dependencies
    f
    f
    Contact
    has_many :categorizations
    has_many :categories, through: :categorizations
    Category
    has_many :categorizations
    has_many :contacts, through: :categorizations
    Contact.delete_all
    DELETE FROM `contacts`
    Contact.destroy_all
    

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64. destroy_all vs. delete_all with
    has_many dependencies
    f
    f
    Contact
    has_many :categorizations
    has_many :categories, through: :categorizations
    Category
    has_many :categorizations
    has_many :contacts, through: :categorizations
    Contact.delete_all
    Contact.destroy_all
    DELETE FROM `contacts` WHERE `contacts`.`id` = 1
    DELETE FROM `contacts` WHERE `contacts`.`id` = 2
    DELETE FROM `contacts` WHERE `contacts`.`id` = 3
    

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65. destroy_all vs. delete_all with
    has_many dependencies
    category = Category.where(name: “Networking”).first
    category.contacts.destroy_all
    

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66. destroy_all vs. delete_all with
    has_many dependencies
    category = Category.where(name: “Networking”).first
    category.contacts.destroy_all
    It looks like you’re
    trying to delete some
    records, do you need
    help with that?
    

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67. destroy_all vs. delete_all with
    has_many dependencies
    category = Category.where(name: “Networking”).first
    category.contacts.destroy_all
    category.categorizations.destroy_all
    It looks like you’re
    trying to delete some
    records, do you need
    help with that?
    

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68. destroy_all vs. delete_all with
    has_many dependencies
    category = Category.where(name: “Networking”).first
    category.contacts.destroy_all
    category.categorizations.destroy_all
    category.categorizations.delete_all
    It looks like you’re
    trying to delete some
    records, do you need
    help with that?
    

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69. CollectionProxy
    

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70. CollectionProxy
    Object that holds
    the association
    category
    

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71. CollectionProxy
    Object that holds
    the association
    category
    Associated object
    categorizations
    

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72. destroy_all vs. delete_all with
    has_many dependencies
    f
    f
    Contact
    has_many :categorizations
    has_many :categories, through: :categorizations
    Category
    has_many :categorizations
    has_many :contacts, through: :categorizations
    category.categorizations.delete_all
    

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73. destroy_all vs. delete_all with
    has_many dependencies
    f
    f
    Contact
    has_many :categorizations
    has_many :categories, through: :categorizations
    Category
    has_many :categorizations
    has_many :contacts, through: :categorizations
    category.categorizations.delete_all
    UPDATE `categorizations` SET
    `categorizations`.`category_id` = NULL WHERE
    `categorizations`.`category_id` = 1
    

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74. destroy_all vs. delete_all with
    has_many dependencies
    Contact
    has_many :categorizations, dependent: :destroy
    has_many :categories, through: :categorizations
    Category
    has_many :categorizations, dependent: :destroy
    has_many :contacts, through: :categorizations
    category.categorizations.delete_all
    f
    f
    

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75. destroy_all vs. delete_all with
    has_many dependencies
    Contact
    has_many :categorizations, dependent: :destroy
    has_many :categories, through: :categorizations
    Category
    has_many :categorizations, dependent: :destroy
    has_many :contacts, through: :categorizations
    category.categorizations.delete_all
    DELETE FROM `categorizations` WHERE
    `categorizations`.`id` = 1
    DELETE FROM `categorizations` WHERE
    `categorizations`.`id` = 2...
    f
    f
    

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76. destroy_all vs. delete_all with
    has_many dependencies
    f
    f
    Contact
    has_many :categorizations, dependent: :delete_all
    has_many :categories, through: :categorizations
    Category
    has_many :categorizations, dependent: :delete_all
    has_many :contacts, through: :categorizations
    category.categorizations.delete_all
    

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77. destroy_all vs. delete_all with
    has_many dependencies
    category.categorizations.delete_all
    user system total real
    => 130.080000 0.120000 130.200000 (130.308334)
    

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78. destroy_all vs. delete_all with
    has_many dependencies
    category.categorizations.delete_all
    user system total real
    => 130.080000 0.120000 130.200000 (130.308334)
    DELETE FROM `categorizations` WHERE
    `categorizations`.`category_id` = 1
    

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79. destroy_all vs. delete_all with
    has_many dependencies
    category.categorizations.delete_all
    user system total real
    => 130.080000 0.120000 130.200000 (130.308334)
    DELETE FROM `categorizations` WHERE
    `categorizations`.`category_id` = 1 AND
    `categorizations`.`id` IN (1, 2, 3, 4, 5, 6, 7, 8, 9,
    10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22,
    23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35,
    36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46...10000)
    

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80. Let’s fix this.
    category = Category.where(name: “Networking”).first
    Categorization.where(
    category_id: category.id).delete_all
    

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81. Let’s fix this.
    category = Category.where(name: “Networking”).first
    Categorization.where(
    category_id: category.id).delete_all
    user system total real
    => 0.010000 0.000000 0.010000 ( 0.014286)
    

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82. Let’s fix this.
    category = Category.where(name: “Networking”).first
    Categorization.where(
    category_id: category.id).delete_all
    user system total real
    => 0.010000 0.000000 0.010000 ( 0.014286)
    DELETE FROM `categorizations` WHERE
    `categorizations`.`category_id` = 1
    

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83. In Conclusion
    

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84. In Conclusion
    ‣ Active Record is an awesome tool
    

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85. In Conclusion
    ‣ Active Record is an awesome tool
    ‣ Active Record queries can have major consequences
    

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86. In Conclusion
    ‣ Active Record is an awesome tool
    ‣ Active Record queries can have major consequences
    ‣ We can all be friends with Active Record
    

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87. In Conclusion
    ‣ Active Record is an awesome tool
    ‣ Active Record queries can have major consequences
    ‣ We can all be friends with Active Record
    ‣ Check out these helpful tools
    

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88. In Conclusion
    ‣ Active Record is an awesome tool
    ‣ Active Record queries can have major consequences
    ‣ We can all be friends with Active Record
    ‣ Check out these helpful tools
    New Relic
    

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89. In Conclusion
    ‣ Active Record is an awesome tool
    ‣ Active Record queries can have major consequences
    ‣ We can all be friends with Active Record
    ‣ Check out these helpful tools
    New Relic
    MiniProfiler Gem
    

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90. In Conclusion
    ‣ Active Record is an awesome tool
    ‣ Active Record queries can have major consequences
    ‣ We can all be friends with Active Record
    ‣ Check out these helpful tools
    New Relic
    MiniProfiler Gem
    Bullet Gem
    

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91. much thanks
    so database
    many Active Record
    very mwrc
    such data
    wow
    

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92. eileencodes.com
    @eileencodes
    speakerdeck.com/eileencodes
    github.com/eileencodes/crud_project
    Eileen M. Uchitelle
    

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